Lemon RX
Stabilizer PLUS 7-Channel Receiver
Reference Guide
Contents
An Introduction to the Lemon Stabilizer PLUS .....................................................................................1
Using the Lemon StabPLUS .................................................................................................................3
Capability with Various Transmitters ........................................................................................................ 3
Optional Ways to Use the StabPLUS ......................................................................................................... 4
Transmitter and DIP Switch Setup ............................................................................................................ 5
Receiver and Servo Power Supply ............................................................................................................ 6
Dual Rates and Expo in the Transmitter ................................................................................................... 7
Installation ........................................................................................................................................7
Orientation of the Receiver Unit ............................................................................................................... 7
Mounting .................................................................................................................................................. 9
Minimizing Vibration ................................................................................................................................ 9
Setting up Stabilization .................................................................................................................... 10
Stabilizer Response and Direction .......................................................................................................... 10
Gain Adjustments ................................................................................................................................... 11
Setting Stabilizer Gain Pots................................................................................................................. 11
Optimizing Gain .................................................................................................................................. 11
Autolevel Gain .................................................................................................................................... 12
Master Gain Control ............................................................................................................................... 12
Resetting the Stabilizer ........................................................................................................................... 13
Resetting Stabilizer Level .................................................................................................................... 13
Resetting Stick Neutrals...................................................................................................................... 14
Initial Test Flying with Autolevel mode ................................................................................................... 15
Controlling the Way it Works .................................................................................................................. 15
Selecting the Operational Method ..................................................................................................... 15
Selecting the Mode ............................................................................................................................ 16
How Mode Control Works .................................................................................................................. 17
Changing Mode Order and Autolevel Setting..................................................................................... 17
Mode Change and the “Toggle” Gesture ........................................................................................... 18
Using a Two-Position Switch to Control Stabilization ......................................................................... 18
Startup ............................................................................................................................................ 19
Binding .................................................................................................................................................... 20
Stabilizer Condition after a Rebind..................................................................................................... 21
Failsafe Options ...................................................................................................................................... 21
Understanding the Three Different “Calibrations" ................................................................................. 22
Why the Gyros Need Occasional Recalibration .................................................................................. 23
What the LEDs Mean .............................................................................................................................. 23
Lemon Stabilizer PLUS Receiver – Reference Guide
Further Options ............................................................................................................................... 24
Stabilizer Always-ON............................................................................................................................... 24
Hardware Reset ...................................................................................................................................... 25
Mixing ............................................................................................................................................. 25
Mixing and the Lemon Stabilized Receiver ............................................................................................. 25
WARNING: Flaperons and Aileron Differential ....................................................................................... 27
Stabilizer Modes: Gyro vs. Autolevel ................................................................................................. 28
Appendices ...................................................................................................................................... 32
Appendix 1: Diversity and RSSI ............................................................................................................... 32
Appendix 2: Range Checking .................................................................................................................. 36
Appendix 3: Versions of the Lemon StabPLUS Receiver ......................................................................... 37
Appendix 4: Using the StabPLUS with a DX6i ......................................................................................... 38
Appendix 5: Using an Open Source Transmitter (Taranis, 9XR, etc.) ...................................................... 39
Appendix 6: Throttle “Drift” in Autolevel Mode..................................................................................... 40
2017-03-03
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Lemon Stabilizer PLUS Receiver – Reference Guide
Lemon Rx Stabilizer PLUS
A DSMX compatible Receiver with Integrated Stabilizer
Identification of components
An Introduction to the Lemon Stabilizer PLUS
The Lemon 7-channel Stabilizer PLUS (referred to from now on as the StabPLUS) is a versatile integrated,
full range, DSMX compatible receiver and stabilizer, primarily intended for electric models, but suitable
for use with some IC (fuel-powered) models too. It is a development of the original Lemon Stabilizer with
some additional features, including an Autolevel mode, but does not replace it.
The Lemon philosophy is that the StabPLUS should be simple to set up without using any PC, smart
phone or programming box for configuration. In the words of the CEO, “It is designed for the flier who
does not want to spend time with a graphical interface for various settings but just wants to enjoy flying
at the field, using a screw driver to set just about anything easily and quickly. I also think that too much
autonomous capability would make the plane become an FPV for aerial photos. Just not fun to fly.”
The Lemon StabPLUS is very small and light. Despite its low cost, it offers both high quality and high
performance. The Lemon StabPLUS is available with dual diversity antennas for enhanced reliability of
the radio link.
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Lemon Stabilizer PLUS Receiver – Reference Guide
The StabPLUS automatically switches from DSMX® to DSM2® and so will work with most Spektrum®
technology transmitters, including the basic DX4e and DX5e units and the popular DX6i, as well as
computer transmitters such as DX6, DX7s, DX8 (both versions) and DX9 and the JR9303/9503. It can also
work with open source transmitters such as Taranis and Turnigy 9XR using an add-on DSM2 or DSMXcompatible module, although not all available modules necessarily work correctly.1
Organization of the Instructions
For basic step-by-step guidance in setting up and using the Lemon StabPLUS, go to the Essential
Instructions, available at:
https://www.rcgroups.com/forums/showpost.php?p=29478801&postcount=4
This Reference Guide is intended to provide additional material on installing, using and understanding the
StabPLUS, as well as optimizing the reliability of the radio link. Because it is a reference guide it may
include some repetition of material in different sections. For simplicity, a first reading should skip over the
footnotes which provide clarifications or explanations of exceptions and special cases. Do come back and
reread them however as there may be some important information for particular situations.
These documents are prepared by jj604 (John) and Daedalus66 (Nigel). We have worked closely with the
people at Lemon RX but are not paid by, or associated with, the manufacturer.
The Lemon 7 channel StabPLUS combines the ease of use and performance of the regular Lemon Rx 7Channel Stabilizer with enhanced features that give greater flexibility and security of operation. In
addition to the three internal gyros, which allow normal Gyro (rate) stabilization, the PLUS adds three
accelerometers, which make it possible to sense the direction of “down” and therefore enable automatic
leveling.2 The StabPLUS has three possible operating modes, depending on the capability of your
transmitter:

OFF (no stabilization)

Gyro (rate stabilization)

Autolevel (self-level plus limited bank and pitch)
In addition, Autolevel mode has two settings: Beginner (very restricted roll and pitch angles) and
Advanced (much greater maximum angles).
The StabPLUS provides built-in mixing capability for elevon (delta) and V-tail, and supports dual ailerons
on separate channels. Note, however, that flaperons and aileron differential cannot be used when in
Autolevel mode.3
The StabPLUS is available with two types of antenna: a single short antenna, which is suitable for most
line-of-sight flying, or twin diversity antennas to provide even greater radio link reliability. Top-pin and
end-pin options are available in the twin antenna “diversity” version. The single antenna version is
available only in top-pin configuration.
1
In particular the Spektrum DM8 and DM9 modules and some versions of the OrangeRX transmitter module are
known not to work reliably with this receiver. Always range test any particular combination before flight.
2
You will sometimes see the regular Lemon Stabilizer called (confusingly) a 3-axis and the StabPLUS a 6-axis
stabilizer. The stabilizer only corrects in the three flight axes no matter how many gyros/accelerometers it has.
3
See page 27.
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Lemon Stabilizer PLUS Receiver – Reference Guide
The StabPLUS has been designed to be as easy as possible to use and to serve as a “drop-in” replacement
with added Autolevel functionality for the original seven channel Lemon Stabilizer.
Don’t think of the StabPLUS as a low cost Spektrum SAFE® system. While it has some of the features of
the SAFE approach, the StabPLUS should be seen as an excellent rate stabilizer with some additional
limited Autolevel functionality. The integration of a proven DSMX receiver and well-optimized stabilizer
satisfies one main design aim of simple installation in electric powered models.
At a minimum, the StabPLUS uses the four flight4 control channels (TAER), plus channel 5 (Gear) for
control of stabilizer mode. The maximum capability of the StabPLUS, with an eight or more channel
transmitter and in Always-ON configuration, is to use channels 1 to 7 for flight control, flaps, landing gear,
etc. and have in-flight adjustable stabilizer gain on channel 8.5
Using the Lemon StabPLUS
Capability with Various Transmitters
The minimum number of transmitted channels required in order to use the stabilizer with a
conventionally configured, electric-powered, three-axis plane without any additional features like
retracts or flaps is five.
That covers the four flight channels: Throttle (channel 1), Aileron (channel 2), Elevator (channel 3) and
Rudder (channel 4); plus Gear (channel 5) to switch the stabilizer on and off in flight.
All full range Spektrum transmitters have at least five controllable channels and thus can be used with
the Lemon stabilizer.6 The computer transmitters offer the following possibilities.
With a DX6i, DX6 or DX6e, Aux1 (channel 6) can be used to control one of three main possibilities:

Retracts, or

Flaps, or

A second aileron servo (as in a dual aileron setup).
A DX7 or DX7s enables the use of Aux2 (channel 7); thus a 7-channel transmitter enables any two of the
above three possibilities.
A DX8 or higher transmitter enables internal use of Aux3 (channel 8), giving Master Gain control. It does
not provide an additional free channel.
Note that no amount of transmitter mixing can change the receiver’s use of channel 5 (commonly
labeled Gear) or channel 8 (commonly labeled Aux3). These channels are committed within the receiver
to stabilizer Mode and Master Gain respectively. You can on some transmitters adjust which switches,
knobs or sliders control those channels, or you may be able to use mixes from other channels for this
purpose, but these channel assignments within the receiver cannot be altered.
4
The StabPLUS is designed for aileron control, but some people report using it successfully in three channel
models (Rudder, Elevator, Throttle) by plugging the rudder servo into the aileron channel.
5
The Stabilizer PLUS has user pre-set failsafe (which the original Stabilizer lacks) and so is suitable for use with
internal combustion (fuel) powered models. If you intend to use it in an IC model (gas or glow), please read
“Minimizing Vibration” on page 9.
6
Gear (channel 5) is operated by the ACT/Aux switch on a DX4e and the Ch 5 switch on a DX5e.
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Lemon Stabilizer PLUS Receiver – Reference Guide
It follows from all this that you cannot on a conventional powered model have Stabilizer Mode control
plus all three of: dual ailerons and independent flaps and independent gear, even with an 8-channel
transmitter. There are simply not enough channels available in the Lemon receiver.
The exception to all this is that the StabPLUS provides an Always-ON capability, which allows the
stabilization to be turned on (either Gyro or Autolevel) permanently. This frees up channel 5 for other
uses, such as retractable landing gear but loses the in-flight OFF switch.
To summarize, practical arrangements for a powered plane, using a seven or more channel transmitter
and a StabPLUS receiver with channel 5 for in-flight mode control include:

A single Aileron servo (or two servos on a Y-cable) on Ail (channel 2), with Flaps on Aux1
(channel 6) and Retracts on Aux 2 (channel 7);

Separate Aileron servos on Ail (channel 2) and Aux1 (channel 6), with Retracts OR flaps on Aux 2
(channel 7); this arrangement would allow use of the flaperon function in Rate mode.
Using Always-ON makes one more channel available. So you can have separate Aileron servos on Ail
(channel 2) and Aux1 (channel 6), with Flaps on Aux 2 (channel 7) and retracts on Gear (channel 5).
Optional Ways to Use the StabPLUS
The StabPLUS can be set up to operate in three different ways. The options are:
1. With stabilization turned permanently OFF. It then acts as a normal 7 channel non-stabilized
receiver. This option is set when the white DIP switches J4 and J5 are both Off.
2. With stabilization mode switched by channel 5. This is the most common way and leaves 6
channels available for flight controls. Channel 5 output is unavailable for most practical purposes.
This is the most likely way to use the StabPLUS.
3. With stabilization turned permanently ON. Using the Always-ON setting, Channel 5 is available
and is commonly used for Gear. However the stabilization mode cannot be changed, nor can
stabilization be turned off in flight. 7
The table below provides a detailed chart of the various combinations of control functions available with
transmitters that have different capability.
1
2
3
4
5
6
7
8
Thr
Ail
Ele
Rud
Gear
Aux1
Aux2
Aux3
Pins
2
3
4
5
6
7
1
None
Stab OFF
Throttle
Ail/RAL
Elevator
Rudder
Gear
Aux1/LAL
Bind/Aux2
–
Stab ON
Throttle
Ail/RAL
Elevator
Rudder
(Mode) *
Aux1/LAL
Bind/Aux2
(Gain)
Always-ON
Throttle
Ail/RAL
Elevator
Rudder
Gear
Aux1/LAL
Bind/Aux2
(Gain)
Channel
* Although the channel 5 (Gear) signal appears on these pins, it is not useful as it changes with the mode command
(unless the StabPLUS is set to Always-ON or stabilization is disabled by setting J4 and J5 to off).
7
If you have an eight channel or better transmitter you can reduce Master Gain to zero (or very low), which
effectively shuts stabilization off. See “Master Gain Control” on page 12.
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Lemon Stabilizer PLUS Receiver – Reference Guide
Transmitter and DIP Switch Setup
The transmitter channel setup, as well as DIP switch settings and wing type, are shown below for all
supported configurations.
Check that the servos and ESC are in the appropriate slots on the receiver. Because it is used internally by
the receiver to turn stabilization on/off, normally the Gear slot (channel 5) will be empty. This is
indicated by the XXX in the lists below. Set switches J4, J5 and J6 on the receiver as indicated below.
For recent Spektrum transmitters, set the Aircraft Type menu as shown. In all cases, including V-tail, the
tail type is Normal.
Note that mixing for elevons or V-tail is ALWAYS done in the stabilizer; the transmitter MUST NOT be
programmed for elevons or V-tail.
Transmitter and Switch Configurations
Conventional controls with single aileron servo or two aileron servos with a Y-cable:
Channels: 1 –THR, 2 – AIL, 3 – ELE, 4 – RUD, 5 – XXX.
Switches: J4 – ON, J – 5 ON, J6 – OFF.
Wing type: Normal.
Conventional controls with aileron servos on separate channels:
Channels: 1 – THR, 2 – R-AIL, 3 – ELE, 4 – RUD, 5 – XXX, 6 – L-AIL.
Switches: J4 – ON, J – 5 ON, J6 – ON.
Wing type: Dual Ail.8
Elevon (Delta wing) control configuration:
Channels: 1 – THR, 2 – R-ELEV, 3 – L-ELEV, 4 – RUD 9, 5 – XXX.
Switches: J4 – ON, J – 5 OFF, J6 – OFF.
Wing type: Normal (NOT Delta).
V-tail control (single aileron servo or Y-cable):
Channels: 1 – THR, 2 – AIL, 3 – R-TAIL, 4 – L-TAIL, 5 – XXX.
Switches: J4 – OFF, J – 5 ON, J6 – OFF.
Wing type: Normal. Tail type: Normal (NOT V)
V-tail control (separate aileron servos):
Channels: 1 – THR, 2 – R-AIL, 3 – R-TAIL, 4 – L-TAIL, 5 – XXX, 6 – L-AIL.
Switches: J4 – OFF, J – 5 ON, J6 – ON.
Wing type: Dual Ail or Flaperon.8 Tail type: Normal (NOT V).
Important safety warning: Leave the motor unconnected or remove the propeller when testing or
programming. Electric models can bite!
8
Flaperon wing type can also be used, BUT read the important WARNING on page 27 before activating a Flaperon
configuration.
9
Only used if the model has a separate vertical rudder.
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Lemon Stabilizer PLUS Receiver – Reference Guide
This table pulls the information together for easy reference:
Summary of Settings for Various Control Configurations
Wing
Type
Channel Assignments
Model Type
1
2
3
4
5*
6
7**
Conventional
(one ail channel)
Thr
Ail
Ele
Rud
Mode
?
?
Conventional
(two ail channels)
Thr
RAil
Ele
Rud
Mode
LAil
?
Elevon/
Delta Wing
Thr
RElev
LElev
Rud
Mode
?
?
V-Tail
(one ail channel)
Thr
Ail
RTail
LTail
Mode
?
?
V-Tail
(two ail channels)
Thr
RAil
RTail
LTail
Mode
LAil
?
8***
Master
Gain
Master
Gain
Master
Gain
Master
Gain
Master
Gain
Stabilizer
Switches
J4
J5
J6
Normal
✔
✔
X
Dual Ail
✔
✔
✔
Normal
✔
X
X
Normal
X
✔
X
Dual Ail
X
✔
✔
“?” indicates available for any function (such as Gear or Flaps).
* If the StabPLUS is set to Always-ON, channel 5 (Gear) becomes available for other functions.
** Use of Channel 7 (Aux2) requires a transmitter with more than six channels such as a DX7/8/9.
*** Channel 8 (Aux3) is internally wired for Master Gain and is not usable for any other function.
Receiver and Servo Power Supply
The Lemon StabPLUS has a supply Voltage Range of 3.45 – 7.2V. A standard 5V or 6V BEC, or a 4 or 5 cell
NiMH pack are common power sources. A 2S LiFe receiver pack is also suitable (7.2V). A 2S LiPo pack,
however, is NOT suitable, as it can reach 8.4V when fully charged.
Power supply in all stabilizer installations is more critical than for an unstabilized receiver, as the
stabilizer works the servos more frequently and harder than a human pilot does. But for an autolevelling
stabilizer like the StabPLUS reliable power is even more important than for a simple rate stabilizer (like
the regular Lemon). The reason is that if the autolevelling stabilizer loses power for any significant time it
will go through an initialization routine. You will have no control during this time. The StabPLUS has a
very high tolerance for short power drops (brown outs) but if they exceed about a second it will restart
itself and be out of action for up to 20 seconds.
Lemon recommend using a stand-alone BEC, or ESC with integral BEC, that has 50% more current
capacity than is required in a non-stabilized setup. In practice BECs commonly come in 3A and 5A sizes.
For smaller park flier planes an integrated or separate 3A BEC will normally do fine; a switching-type is
preferable to a linear one. In larger planes a separate 5A switching BEC is probably good insurance. In
some cases an even larger BEC may be advisable depending on the servos size and load.
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Lemon Stabilizer PLUS Receiver – Reference Guide
Dual Rates and Expo in the Transmitter
Dual Rate adjusts the amount of response of the control surface to transmitter inputs. Many transmitters
allow use of triple rates for more variety in adjustment of control throw.
At 100% setting of D/R, the throw is as set in the Travel menu under Servo Setup in recent Spektrum
transmitters. D/R enables the rate to be reduced for smoother control. A good starting point for D/R is to
set High Rate at 100% and Low Rate at 65-75% for each axis.10
Expo works with D/R to change the control response from linear to an S-curve, flattened around neutral
and steeper as the stick approaches the ends of its travel. In effect, on Spektrum transmitters positive
expo gives a lower control rate around neutral and progressively higher rates at bigger stick movements.
A typical Expo value of 20-30% softens response around neutral and can make smooth flying easier.
Stabilization settings also affect the response of the model to the transmitter sticks, typically reducing
sensitivity with an expo-like effect. To achieve your preferred response, you may need to adjust your
rates and expo once you find out how the model reacts.
Note that for OFF and Gyro modes, the dual rate and expo settings determine stick response but don’t
affect how the stabilization works. That is entirely done within the stabilizer.
Things are different in Autolevel, in that aileron and elevator control throw, together with the setting of
Autolevel to Beginner or Advanced, directly determine the maximum angles of bank and pitch possible.
Consequently, for optimum control, 100% rate and no expo is normally used in Autolevel mode.
Installation
Orientation of the Receiver Unit
The stabilizer must be installed with the pins toward the tail of the aircraft and aligned with the
centerline but four orientations are available

Upright with DIP switches pointing to sky.

Inverted with DIP switches pointing to ground.

Vertical with DIP switches pointing to left or right of the aircraft.
The most common arrangement is to mount the stabilizer level and upright, aligned with the centerline
of the fuselage, with the connector pins toward the tail.
The StabPLUS autosenses its orientation if you do an initial calibration toggle gesture and will work
properly if rotated 90˚ on the roll axis. This means that you can fasten it to the flat side of a profile
aircraft. A common arrangement that also presents no problems is mounting the stabilizer upside down
for access from the bottom of the model.
It should not however be rotated so that the pins are facing forward. The stabilizer has not been tested
for operation this way.11
10
If using a DX4e, DX5e or DXe, the built-in D/R function gives rates of 100% (Position 0) and 75% (position 1).
11
Some users with difficult installation issues have reported success when mounting the stabilizer with pins
forward. Lemon advise that this may work satisfactorily but they have not tested it under all conditions and
therefore they do not recommend it.
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Lemon Stabilizer PLUS Receiver – Reference Guide
Not only must the stabilizer be correctly oriented in the model but it is also influenced by the actual
positioning. It is a good idea to place a stabilizer that contains accelerometers like this one does as close
to the CG of the plane as is reasonably practical. Although a good principle, in practice people have
found that stabilizers such as the Lemon PLUS still work quite effectively when placed some distance
from the CG – although sensitivity and precision may be affected a little.
During the initialization process, the accelerometers determine the direction of maximum gravitational
force and identify that as “Down”. This is then recorded as the Z axis of the stabilizer. Whenever auto
leveling is engaged the stabilizer attempts to control the aircraft so that the current down direction
aligns with the Z axis. It really only needs to know which axis is the Z axis and the direction of the current
gravity force in able to do this. The effect is to bring the stabilizer back to the same orientation it was
when it was initialized and with the X and Y axes level. It depends for accuracy on the stabilizer being
correctly mounted in the aircraft. If the stabilizer is misaligned during installation then the aircraft will fly
in a misaligned way. The pitch/roll offset calibration process on page 13 will correct for this by setting an
offset that the stabilizer remembers until the power is removed. The plane has to be held level during
this initialization.
What does this mean in practice?
The stabilizer only needs to know which direction is “down” and establishes this from the direction of
earth’s gravity sensed by the inbuilt accelerometers. It then knows where the Z axis should point (up and
down) when auto leveling is initiated. When that happens it manages the control outputs to attempt to
make the bottom of the stabilizer level. That is, the stabilizer will control the plane such that the circuit
board (or the bottom of the case) will be normal to the gravity vector. Normal as used here is a
mathematical term meaning a line that is at right angles to a flat surface.
Because of this it is important to place the stabilizer “flat” in the plane. To emphasize, unlike some other
auto leveling stabilizers, if you do not do a deliberate toggle, level flight attitude is NOT set by default as
the attitude of the plane at power on but by the alignment of the stabilizer in the airframe. This makes it
simpler and fairly foolproof but only if you mount the stabilizer level. The pitch/roll offset calibration
process can be done during the 9 seconds of Indicator 1 flashing and will set an offset that the stabilizer
remembers, even when the
power is removed
However this all assumes the
3 flight control sticks are at
standard neutral with no trim.
If the sticks are deflected or
trim is applied in Auto level
mode, the stabilizer thinks
you want to pitch or roll the
plane and will move the
controls to respond in the
correct direction. What it will
try and do is make the z axis
line up with gravity PLUS
some deflection angle set by
the sticks. Clearly if you apply
trim to make the plane fly
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Lemon Stabilizer PLUS Receiver – Reference Guide
level with the stabilizer off, then you switch it to auto level, the stabilizer will attempt to change the pitch
or roll angle because it thinks you want to initiate that response.
To accommodate this, the stabilizer is able to reset what it thinks is stick neutral if you do a toggle of
channel 5 at any time.
In practice what this means is you can trim the plane to fly as you want it, then do a toggle of the
channel 5 switch. This tells the stabilizer to treat the current trim and/or stick position as “neutral stick”.
The setting will remain until you toggle again and is not reset at power on. This toggle reset avoids
having to mechanically adjust a model to fly precisely level when the trims and sub trims are set at zero.
Lemon recommends that you do this when the plane has landed back on the ground and is stationary. It
is possible to do a trim toggle in flight but results may sometimes be unpredictable.
HINT
Don’t get too caught up in this. Lemon have tried to make everything as simple as possible. Provided you
install the stabilizer flat in the plane with its case aligned with level flight direction, and avoid excessive
transmitter trim or sub trim, a level reset is often not needed. Only Auto level is affected anyway, not
Gyro (Rate) stabilization. If you do see significant climb/dive or roll when you switch to Autolevel mode,
it may be a sign that your model has too much transmitter trim; you should correct for this by doing a
trim reset toggle or even better by adjusting the controls mechanically if possible.
Mounting
All stabilizers must be protected from vibration and shock, yet attached securely enough to follow the
movements of the model and cannot come loose. The double-sided mounting tape provided with the
Lemon StabPLUS offers the simplest solution. Use it to attach the receiver in the appropriate attitude to
a flat surface in the model. Make sure the surface is clean, the attachment is secure and the receiver
case is not touching any part of the model. Good quality servo-mounting tape or 3M (Scotch) Permanent
Outdoor Mounting Tape is also suitable for this purpose. Do not use the common indoor white foam
mounting tapes.
Mounting with adhesive tape can make subsequent removal of the unit difficult. Accordingly, Velcro®type tape can be used. Cover the whole bottom of the receiver with the fuzzy (loop) side of the material.
Use a patch of the hook-side material at least as big as the case to avoid the possibility of the stabilizer
wobbling. Check to make sure the stabilizer is firmly attached as if not the stabilizer will be trying to level
itself and not the model in Auto level mode.
Be careful when removing the receiver, as the case is only held together by two small screws and two
friction pegs. To provide reinforcement, you may wish to apply transparent tape to the case sides.
These methods are suitable for electric-powered models, but may not provide sufficient isolation in the
harsher environment of a fuel-powered (IC) model.
Minimizing Vibration
Autolevel stabilizers are particularly susceptible to vibration. It is therefore very important, even for an
electric model with a properly mounted receiver, to eliminate sources of vibration. Balance the propeller
and check for any out-of-true running of the motor shaft or bearings. A well-balanced electric model
should show no noticeable vibration in any part of its speed range.
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Lemon Stabilizer PLUS Receiver – Reference Guide
Internal combustion (IC) engines are however vibration generators and there is little you can do to stop
that. Be aware that flight stabilizers can be adversely affected by regular significant vibration and there is
no simple single solution. The StabPLUS has been designed with additional vibration rejection software
and should perform better than some other stabilizers but there is no guaranteed straightforward
solution that fits all cases. People have had success using the anti-vibration mounts sold for FPV cameras
and with various DIY solutions which normally rely on a mounting tray suspended by rubber bands from
the vibrating airframe. Addition of weight to the tray to lower its resonant frequency can help but the
calculation of such a solution is not straightforward. The best advice for anyone wanting to use the
StabPLUS in an IC powered aircraft is to try it and see but make sure you can turn stabilization off in a
hurry. You may be fortunate and find there is no issue – or you may not. Vibration problems normally
show themselves as erratic control behavior or by a constant drift from the set Autolevel attitude,
sometimes after a stable period.
Setting up Stabilization
Stabilizer Response and Direction
The starting point for stabilizer adjustment is with the three onboard gain adjustment pots set at
12 o’clock (straight up). If Master Gain (channel 8) is available, set it in middle position; check the
transmitter’s Monitor screen to make sure Master Gain is at 0%, corresponding to a Gain of 1x.
The diagram shows how the surfaces should respond to movement of the model about each axis. It is
easier to see this in Auto level mode. When the model is rolled to the right, the right aileron should go
down and the left aileron up to resist the displacement. Likewise, when the model pitches nose-down,
the elevator should go up to compensate. And when it yaws nose-right, the rudder should go left.
However the rudder will only “pulse” then return to neutral. It does not stay deflected.
In Gyro mode, the stabilizer only applies a brief “pulse” of correction in all three axes. The stabilizer
knows nothing about the position and attitude of the model, it just responds to momentary outside
disturbances. This is ideal for making the model fly more smoothly, much like a bigger and heavier plane,
and does not unduly limit the pilot’s ability to control the model.
By contrast, Autolevel mode introduces a quite different style of control in the pitch and roll axes. In
Auto level mode the sticks directly control the attitude of the plane not the deflection of the control
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Lemon Stabilizer PLUS Receiver – Reference Guide
surfaces. The stabilizer decides how much surface deflection to give in order to achieve the commanded
attitude. The result is that if the sticks are neutral and you deflect the model and hold it at a tilt or roll
angle, the elevator or ailerons will deflect and stay deflected. The stabilizer is waiting for the plane to
level out before restoring the surfaces to zero deflection.
If you find it hard to see the surface movement, temporarily increase the gain by turning the pots fully
clockwise or try putting your finger on the hinge line. It is very easy to tell the direction by feel.
THIS NEXT THING IS VITALLY IMPORTANT:
If stabilization moves the surfaces the wrong way (i.e., to increase the disturbance) your
model will be uncontrollable in flight (until you switch off stabilization)!
To correct this, change the appropriate switch: J1 (aileron), J2 (elevator) or J3 (rudder).
Just as experienced RC pilots check stick directions before the first flight of the day, so a pilot using a
stabilizer should check that the surfaces move correctly in response to a disturbance.
Gain Adjustments
Setting Stabilizer Gain Pots
Gain is normally set in Gyro mode to achieve maximum
stabilization short of causing oscillation at higher speeds.
It is recommended in the Essential Instructions to set
the three gain pots at about the 12 o’clock position as a
good starting point for many models, but this could
show some oscillation at high speeds. You may prefer
10 o’clock as a more conservative starting point that will
still produce noticeable stabilization. For most models,
at least one or two gain settings will need to be
increased or decreased during flight testing to achieve
optimum stabilization.
Many models fly with gains between 10 o’clock and 2
o’clock but some may require minimum gain (< 8 o’clock)
and some maximum gain (> 4 o’clock) on a particular
channel. There is no hard rule and gains can only be fine-tuned by observing the behavior of the model
at various speeds during flight testing.
The StabPLUS gain settings usually need to be higher to achieve a given level of stabilization than those
of the regular Lemon Stabilizer.
Optimizing Gain
To optimize the individual gain settings, it’s necessary to perform a couple of test flights in Gyro mode.
This will involve landings to adjust each pot on the receiver, followed by retesting in flight, but the basic
job can be done relatively quickly. It’s a good idea to keep notes. If you have an eight or more channel
transmitter, Master Gain can be used to assist the process.
If you encountered oscillation on any axis during the initial flight, turn down the gain a little for that axis.
Then go through the following steps:
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Lemon Stabilizer PLUS Receiver – Reference Guide

Increase the Rudder pot setting by about two “hours”.

Take off with stabilization OFF. Turn ON at a safe height with the model in level flight. Watch for
oscillation on the yaw axis (“tail wag”). Do a shallow dive to pick up speed and again watch for
oscillation.

Land and adjust the rudder pot as required. If there was no oscillation, even when diving, turn
the pot up further. If there was oscillation, turn the pot down a bit .

Take off and retest. You’re aiming to set the pot fairly close to the maximum gain that doesn’t
produce oscillation in any normal flying. So if necessary, repeat until you encounter oscillation or
reach the maximum.

When satisfied with the rudder gain setting, repeat the process for the elevator setting.

Finally follow the same procedure to set the aileron gain pot. Note that aileron is often the most
sensitive control, so increase gain in moderate steps.
Many people find that on typical models the rudder gain can be quite high (or even full) while aileron
and elevator end up somewhere in the range of 9 o’clock to 2 o’clock, but the settings vary with factors
such as model design, flight speed and control setup.
If you have Master Gain available, you can greatly speed up the process of setting individual gains. In the
air, advance the channel 8 (Aux3) control gradually until you observe oscillation on an axis. Note which
axis, land and turn down the gain on the corresponding pot. Repeat until all three axes are set so that
with the Master Gain at midpoint, there is no oscillation. Turning up Master Gain to 2 or 3 o’clock should
start to show signs of oscillation.
HINT: It’s best to do the initial setup and tuning in fairly calm conditions to avoid confusing stabilizerinduced oscillation with buffeting caused by turbulence. Once you have things adjusted, test the
effectiveness of stabilization by flying in windier weather, turning Gyro stabilization on and off. You
should see a noticeable improvement in smoothness with Gyro stabilization turned on.
Autolevel Gain
Normally, setting the gain level for Gyro mode as described above should ensure a satisfactory gain level
for Autolevel mode. When you switch to Autolevel you may see what appears to be intermittent
“oscillation” even at lower speeds. The model rolls for example and then seems to “bounce back” slightly.
This is characteristic sometimes of Autolevel operation, and is not a problem.
Master Gain Control
If the transmitter has eight channels or more, then Master Gain is available on Aux3 (channel 8) and
controls the overall gain of the stabilizer system. If not, Master Gain is automatically set to 1.
The Master Gain function multiplies the setting of the individual gain pots by a factor that can range
from 0 to 2. In other words, with Master Gain turned full up the gain setting of each individual axis will
be roughly doubled. If turned full down, there will be little or no stabilization on any axis, regardless of
the setting of the pots.
For Master Gain to be useful it is best controlled by a knob, slider or lever on the transmitter. On a
DX8G2, for example, the Right Knob is used (labeled “RKnb” in Channel Assign).
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Lemon Stabilizer PLUS Receiver – Reference Guide
To check operation, make sure Gyro or Autolevel stabilization is ON (green ON or red/green alternating).
Look at the Monitor screen on the transmitter to make sure the value is going from -100% to 100% when
you turn the control through its full range.
You can use channel reverse to change the direction of operation of the knob/slider/lever controlling the
Aux 3 channel. Most people intuitively think of clockwise as increase for a knob and upwards as increase
for a slider or lever.
Understanding Master Gain
Think of the three stabilized channels as the three inputs of a three-channel audio mixer. The on-board
rotary controls or pots (potentiometers) are like the three individual volume controls. The Master Gain is
the overall volume control. It modifies the levels of all three channels, turning them up or down together.
The individual gain values are multiplied by the value of the Master Gain, controlled by Aux3 (channel 8).

With the Master Gain in the center (channel 8 = 0%) the gain value is 1 and the individual gain
values set by the pots are unaffected.

If channel 8 is at -100%, Master Gain is very low and the individual gains become very small.

If channel 8 is at +100%, the Master Gain is nearly 2x and the individual gains have almost twice
their usual effect.
To turn the stabilizer completely off with Master Gain, travel for the low end of channel 8 must be set to
-150%. This is important if you are using a Mix on channel 8 to turn the stabilization function completely
off. Likewise, to get the maximum Master gain value of 2x, channel 8 must be at 150%.
In practice many people initially set channel 8 at 0% (middle position) so that the Master Gain multiplier
is 1x, then they adjust the individual gains to give good stabilization without any oscillation. Master Gain
can greatly help in this process and can subsequently be used to turn the overall gain up or down to suit
changing flight conditions.
Resetting the Stabilizer
Resetting Stabilizer Level
There are two reasons for performing a “Level Reset”: either you have mounted the StabPLUS upside
down, on its side or not quite level in the model, or you need to reset the stabilizer’s sense of level in
order to correct its flight attitude. It’s a good idea to do a level reset any time the model displays any
strange behavior.
Note that Level Reset is mainly about Autolevel behavior. It does, however, serve to inform the stabilizer,
quite literally, which way is up, so is also necessary for Gyro mode use if the stabilizer is mounted on
edge or upside down.
The Essential Instructions provide step-by-step details on the process, but in essence it is as follows.
The fundamental element you need to master is the “Toggle Gesture”:
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Lemon Stabilizer PLUS Receiver – Reference Guide
Toggle Gesture
3-position
Move the Stabilizer Mode switch on your transmitter back
and forth as quickly as possible through its full range for
2-3 seconds. This procedure applies to both 2- and 3-position
switches. At a minimum the stabilizer needs to see six
changes of switch position (see diagram) within 2 seconds,
2-position
but a few more changes are desirable to guarantee a
successful reset.
Assuming that the receiver was previously bound, power up the transmitter. Apply power to the receiver
and note that the Green/Blue LEDs next to the pushbutton will be flashing for about 8-9 seconds.
Within this period complete the Toggle Gesture (above).
If the stabilizer alignment is within +/- 20 degrees of absolute level, the current position of the model will
be used as “level flight”. Successful level calibration will be indicated by the green LED light next to the
header pins flashing four times at the end of the 9 second period. The stabilizer will then leave level
calibration mode and enter whatever normal operation mode is set by the Mode switch (channel 5).
If alignment is NOT within +/-20 degree tolerance (the stabilizer is installed with a large angle offset from
the reference axis in either pitch or roll) or significant movement occurred in the calibration period, the
red LED light next to the header pins will flash twice to indicate failure. You can attempt to calibrate the
unit any time within the 9 seconds period by toggling the switch again.
If no calibration is carried out, or calibration fails after 9 seconds, then 0 degree offset with the reference
axis will be used. That is, if no previous toggle has been done, the stabilizer will assume that its case is
upright (i.e., with label on top). This is fine for a stabilizer mounted flat on the floor, right side up, but can
be catastrophic for an inverted or a side mounted one! If you are using anything other than the default
“level and flat in the model” installation, make sure you get the 4 green LED flashes at some stage
before leaving the ground.
Resetting Stick Neutrals
To ensure optimum stabilizer performance, after any major adjustment of the trims or subtrims you
should use the toggle gesture (as defined above) to reset the stabilizer's values for the stick neutral
positions. This is an entirely separate process from resetting level and can be done at any time after the
stabilizer has completed its initialization. During the reset, the aileron, elevator and rudder sticks and the
corresponding trims must not be moved.
With the transmitter and receiver ON, and leaving the sticks and trims untouched, move the Stabilizer
Mode (Gear) switch as quickly as possible back and forth for at least 2 seconds.
The StabPLUS performs best, especially in Autolevel mode, when trim and subtrim settings are kept to a
minimum. Where possible, use mechanical adjustments to eliminate the need for large trim offsets, then
reset the stick neutrals as described above.
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Lemon Stabilizer PLUS Receiver – Reference Guide
A Practical Note on Stick Centring (resetting stick neutrals)
Do not get over-concerned about stick centering and calibration. The last known good value will be used
even after a power cycle. So the next time when you go to the field with the same plane, just turn on the
transmitter and StabPLUS. The old values will be used until the next toggling.
Under some circumstances, however, such as when trim or subtrim have been set to extremes, the
stabilizer may have difficulty identifying level correctly and require a neutral reset.
Initial Test Flying with Autolevel mode
For initial test flights, after the 9 second calibration period is completed and before taking off, starting in
the OFF position, perform a toggle gesture with the Mode switch to store the neutral positions of the
controls, as described above. This “toggle” should be done before each flight if any of the trims and/or
subtrims are far from zero. This is particularly important if you will be using the Autolevel mode. 12
Check that the stabilizer is turned OFF. Take off and fly around, adjusting trim as necessary. Make sure
the model flies properly without stabilization. If you make major trim adjustments, land and do a toggle
to enable the stabilizer to store the new neutral positions.
At a safe height, use the Mode switch to turn the stabilizer ON in Auto level mode. If the model rolls,
dives or turns suddenly, at least one of the gyro direction switches (J1, J2, J3) is incorrectly set. Switch
OFF the stabilizer immediately! Land and fix. Likewise if you encounter major oscillation, land and reduce
gain in the axis/axes involved.
Assuming the model does nothing scary, continue flying to explore the action of the stabilizer. Do a
shallow dive to pick up speed and watch for oscillation on one or more axes. If it happens, just throttle
back and slow down. Oscillation is quite different from control surface flutter and is generally not
destructive.
Notice how the model handles with the stabilizer turned on. It will be much less responsive in the pitch
and roll axes and the response will be quite different. In Auto level the amount of deflection of the
Aileron and Elevator sticks control the attitude of the plane with respect to the ground not the amount
of deflection of the control surfaces. There is a detailed explanation starting on page 28 which you
should read if you are unfamiliar with Autolevel stabilization. Experiment with dual rate settings. Turn
stabilization off and on to get familiar with its effects.
Controlling the Way it Works
Selecting the Operational Method
The StabPLUS can be set up to operate in three different ways:
1. With stabilization mode switched by channel 5. This is the most common way and leaves six
channels available for flight controls. Channel 5 output is unavailable for all practical purposes
since its output always operates in lock-step with the stabilizer mode selection. This is the
normal default operation as long as either or both of DIP switches J4, J5 is ON.
12
After the first toggle when setting up, and if little trim/subtrim is used, this step can be omitted if you use Gyro
mode. However in Autolevel mode any offset from stick center after trimming a plane’s servo without
“neutralizing” it will cause the stabilizer to shift the plane’s roll or pitch angle and it will not fly level.
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Lemon Stabilizer PLUS Receiver – Reference Guide
2. With stabilization turned on permanently using the Always-ON option. Channel 5 then becomes
available and is commonly used for retractable landing gear. Using this option, the stabilization
mode is fixed on either Gyro or Autolevel, and this cannot be changed in flight. Nor can
stabilization be turned OFF (although with an eight-channel transmitter the same effect can be
obtained by reducing Master Gain to zero, that is -150%).
3. With stabilization deactivated by setting DIP switches J4, J5 and J6 all to OFF. The StabPLUS then
acts as a normal seven channel non-stabilized receiver. There will be no stabilization and no
internal mixing within the receiver.
The Always-ON option is selected by re-binding the stabilizer, waiting for the initialization sequence to
finish, and then setting the Mode switch to either Autolevel (Indicator 2 Red/Green LED alternating
flashes) or Gyro (rate) mode (Indicator 2 Green LED ON).
Now press and hold the button until the Indicator 1 Blue LED is ON solidly, signaling that the stabilizer is
Always-ON in either Autolevel or Gyro mode (as selected during setup). The channel 5 (Gear) output will
no longer have any effect on stabilizer mode and can be used as a normal servo or retract input. The
channel 5 switch, however, can still be used to do the toggle gesture to reset level or stick neutrals.
Remove the bind plug and power cycle the unit.
Selecting the Mode
Stabilizer Off: The stabilizer can be turned off permanently and used as a standard 7 channel nonstabilized DSMX compatible receiver (by setting the on-board DIP switches), OR, if stabilization is active,
the stabilization function can be turned off in-flight using channel 5 as a control.
Gyro (Rate) Mode: In this mode the PLUS functions exactly like the regular Stabilizer, providing rate
stabilization that smooths out flying for fixed wing models, even in windy and turbulent conditions. A
switch moving channel 5 to 0% turns rate stabilization on. If channel 8 (Aux3) is available on the
transmitter, Master Gain can be adjusted in the air to change the overall response sensitivity of the
stabilizer. It modifies the gains set by the three pots on the stabilizer (Aileron, Elevator, Rudder).
Autolevel Mode: The PLUS can be set up to maintain the model in a level attitude, allowing the pilot to
steer it with rudder and/or aileron and control climb and descent rate with elevator and/or throttle. This
mode is intended for beginners needing some assistance, for assistance in landing during gusty
conditions, and for people flying FPV who want to concentrate on the imagery. Note that Autolevel acts
to keep the plane level. It does not know how to maintain a fixed height, as the stabilizer does not
contain an altimeter.
In this mode, the Stabilizer adjusts aileron and elevator control the plane’s flight attitude directly,
keeping it level unless otherwise commanded. Stick deflection angle will directly adjust the bank/pitch
angle of the plane up to a fixed limit.
The Rudder remains unaffected and will move normally according to stick movement but with the
addition of Rate stabilization.
The Stabilizer has no control of throttle. Throttle stick movement controls power to the motor as usual.
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Lemon Stabilizer PLUS Receiver – Reference Guide
How Mode Control Works
This table shows the relationship between the percentage value (switch position) of channel 5 (Gear)
and stabilizer mode for default and alternate orders.
Gear Channel Value
Switch Position
Default Mode Order
(OFF/Gyro/Autolevel)
Alternative Mode Order
(OFF/Autolevel/Gyro)
Function
LED – Indicator 2
Function
LED – Indicator 2
OFF
Red and Green
OFF
Red and Green
Gyro
Green only
Autolevel
Red/Green
alternating
Autolevel
Red/Green
alternating
Gyro
Green only
Position 0
36% to 100%
and beyond
Position 1
35% to -35%
Position 2
-36% to -100%
and beyond
Gyro means basic rate stabilization. The stabilizer will provide an opposite but momentary reaction of
the control surfaces if the plane is disturbed. This is the same functionality as the original 7-channel
stabilizer.
Auto level means that the stabilizer will attempt to bring the plane to an orientation flying straight and
level and will maintain that while the sticks are in neutral. The plane is heavily stabilized and this mode is
suitable for beginners or FPV imaging.
Changing Mode Order and Autolevel Setting
With a bind plug inserted across the top (signal) pins of
channels 4, 5, and 6 and the receiver powered up, the
StabPLUS displays the current state of these two settings.
The transmitter is not required.
The StabPLUS uses the blue/green Indicator 1 lights to
display the Stabilization Mode Order:

Default order: OFF/Gyro/Autolevel – Indicator 1
green flashing

Alternate order: OFF/Autolevel/Gyro – Indicator
1 blue flashing
The Stabilizer uses the red/green Indicator 2 lights to
signal the Autolevel setting:

Beginner setting limits the model to gentle bank and pitch angles – Indicator 2 Green flashing

Advanced setting gives the pilot a greater degree of control – Indicator 2 Red flashing.
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Lemon Stabilizer PLUS Receiver – Reference Guide
To change one or both of the settings, press the receiver button:

for more than 1 second to change the Stabilization Mode Order.

for less than 1 second to change the Autolevel mode.
When the desired changes have been made, power OFF the receiver and remove the bind plug. The
settings will be retained even when the receiver is powered off.
Mode Change and the “Toggle” Gesture
The stabilizer monitors the position of channel 5 and notes any mode changes. It counts as a change
when the value of channel 5 changes from the previous value. It does not matter what the actual values
are, but if the number of changes add up to 6 within any 2 second interval it is regarded as a “toggle”. It
is only the number of changes that matter. For example:
 100% to 0% to -100% on a three-way switch is two changes. Flipping back the other way is two
more. So one-and a half back and forth cycles gets you the necessary minimum of six changes.
 On a two-way switch, one movement is one change. So to get six changes, you have to flip three
full back and forth cycles.
Basically the stabilizer counts the number of “any” changes on the gear channel in comparison to the last
known value. If there are six changes within 2 seconds, a toggle will be triggered. Be aware of this if
using a three-position switch for control. Moving from Off to Rate to Autolevel, then immediately back
again causes no problem since that is four transitions. But moving Off/Rate/Autolevel and back twice
within 2 seconds could unintentionally initiate a trim reset toggle in flight.
Using a Two-Position Switch to Control Stabilization
The ability to set Mode Order facilitates use of the StabPLUS with transmitters lacking a three-position
switch to control channel 5 (Gear). By choosing the appropriate Mode Order, the StabPLUS can be set to
use the two position Gear switch to provide access to either Gyro mode or Autolevel mode, but not both.
Spektrum transmitters with only a two-position channel 5 switch include older examples of the DX4e and
DX5e.
A two-position switch normally provides 100%/-100% output with no middle position. Thus in the
default Mode Order (OFF/Gyro/Autolevel), the switch will select OFF or Autolevel, while Gyro mode will
not be available. Changing the Mode Order to OFF/Autolevel/Gyro will allow the switch to select OFF or
Gyro.
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Lemon Stabilizer PLUS Receiver – Reference Guide
Startup
Assuming a correctly bound receiver and transmitter is on and connected, this is the sequence of
events after the power is applied.
LEDs
Action
What’s happening
STEP 1
Indicator 2 shows rapid
green flash for about 1
second
Model is stationary.
Gyros are internally calibrating.
OR
Indicator 2 shows rapid red
flash for about 1 second
Internal calibration failed and previous
calibration value is used.13
Model has been moved.
STEP 2
Indicator 1 shows slower
rapid green/blue flash for
about 9 seconds
The stabilizer defaults all offsets to zero and uses
the previous orientation information.
The stabilizer will attempt to level the case or use
the previous level setting.
Stabilizer stores all offsets for the current model
position. Orientation information is refreshed.
The stabilizer will attempt to level the model.
Do Nothing
OR
Perform Toggle Gesture
Indicator 2 shows rapid
green flashing for about
1 second
Offset and orientation are valid.
OR
Offset and/or orientation are not valid.14
DO NOT USE IN THIS CONDITION
Indicator 2 shows rapid red
flashing for about 1 second
STEP 3
After about 9 seconds.
Indicator 2 shows the mode
status of the stabilizer:
Red+Green solid = OFF
Green solid = Gyro (rate)
Green/Red flash = Autolevel
Stabilizer is ready for flight.
Any time after 9 seconds
Perform Neutral Reset Toggle
Current transmitter trims are reset to neutral on
the stabilizer. The values are stored until the next
Neutral Reset toggle.
OPTIONS
After binding with bind plug
still in.
After binding with bind plug
still in.
Short press (<1s) sets failsafe to
current stick/switch positions.
Long Press (>1s) sets Stabilizer
to Always-ON mode
Indicator 1 green ON = Pre-set failsafe
Indicator 1 green OFF = No pulse on signal loss
Indicator 1 blue = Always-ON
(Channel 5 “Gear” output available for toggling)
13
The gyro calibration is very stable over long periods of time, so this is normally not a problem.
14
This can be caused if the stabilizer is mounted at an angle of more than 20 degrees from horizontal/vertical.
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Lemon Stabilizer PLUS Receiver – Reference Guide
Binding
See the Essential Instructions for basic information on binding the StabPLUS. Here are a few additional
points.
Binding is the process of “locking” the receiver so that it ignores any other transmitters and is the first
step in setting up any receiver. It is most easily done on the bench, rather than in the model. Ensure that
the transmitter and receiver are separated by 3-6ft/1-2m for binding or the transmitter may “swamp”
the receiver. The Lemon stabilizer has good sensitivity and occasionally it may be necessary to have as
much as 10ft/3m separation to achieve binding, especially in an area of WiFi activity or close to a large
metallic object, such as a furnace.
Generally you should only need to bind once, unless you change transmitters. After binding, normal linkup should not require more than 2-3 feet/1m of separation.
The power source for binding can be:

A receiver pack battery (3.45 - 7.2v); or

A stand-alone BEC (battery eliminator circuit); or

The throttle connection from an electronic speed control (ESC) with built-in BEC.
If using a speed controller as the power source, and it is installed in a model, make sure the motor is
unplugged or the propeller is removed for safety.
Binding can be done with or without servos. Servos plugged in the wrong way round may prevent
binding, so check this if you have difficulty.
If the receiver LEDs don’t flash rapidly to indicate bind mode, you have a problem (such as a reversed
connector). Don’t go any further until you identify the issue and get rapid flashing.
On some transmitters entering bind mode requires holding the Bind or Trainer button/switch while
powering up. Others require opening a menu to enable bind mode. Newer Spektrum transmitters can be
put into bind mode by holding the button (Switch I) while turning on the power switch.
The bind process continues until the receiver internal Red LED stops flashing.15 A solid green or green
and red light on Indicator 2 also indicates a successful bind. Some transmitters will display on-screen
(and/or announce) the type of bind (DSMX/DSM2) and the frame rate (e.g., “22 milliseconds”).
If a successful bind is not achieved, remove power from the receiver and transmitter and repeat the
whole process with the transmitter at a greater distance (e.g., 2 or even 3m). Avoid trying to bind in
close proximity to large metal objects such as chain link fences, vehicles or a furnace. A nearby WiFi
transmitter (e.g., a wireless modem) can also block binding.
When binding is complete, don’t forget to remove the bind plug. If it is left in place it will prevent the
receiver from linking with the transmitter and require a re-bind.
If you didn’t have servos connected while binding, plug in one or more now to channel 2, 3 or 4. Turn the
transmitter back on, then apply power to the receiver. Check that the receiver is operating properly and
15
Transmitters and modules that use a button or switch for binding vary. Some may require it to be held to the end
of the process, while others will not complete until it is released. Releasing when the flashing changes works in
most cases.
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Lemon Stabilizer PLUS Receiver – Reference Guide
that servos respond to the transmitter controls. Check the operation of the channel 5 Mode switch. Look
it the Monitor screen on the transmitter if you have any doubt about how the channels are responding.
Stabilizer Condition after a Rebind
In summary, when you bind the StabPLUS the X, Y, Z installation offset will be assumed to be 0 degrees.
In other words, the level offsets are reset to zero. The receiver is assumed to be placed flat on the floor
of an aircraft at its normal level flight attitude. The aileron, elevator, rudder stick neutral position (as set
by trim and sub-trim values) will be considered as 0%.
Any fail-safe settings already made will not be affected.
Failsafe Options
The Lemon StabPLUS, unlike its predecessor but like most other Lemon receivers, has a Pre-set Failsafe
option in addition to the default No-Pulse Failsafe.
No-Pulse Failsafe
No-Pulse failsafe requires no action on the part of the user. If the receiver loses signal for more than
about a second, it shuts down pulses on all channels. This normally causes the speed control on an
electric model to go to 0% power to the motor. The servos on other channels are left in the positions set
by the last good command. No action is needed by the user, except to ensure that Pre-set failsafe is not
turned on (indicator 1 Green light is not lit).
No-Pulse Failsafe works well within its limitations. The speed control must default to shutting down the
motor if it gets no pulses; modern ESCs do this but it should be tested. No-Pulse failsafe is not acceptable
for use with IC (fuel powered) models.
Pre-set Failsafe
This option causes all channels to go to a preset position on loss of transmitter signal. For example, with
a glider you may choose to set failsafe with a small rudder offset to keep the model circling and perhaps
with Crow braking to guarantee a rapid but safe descent. Some clubs and model insurance policies may
have requirements that failsafe on fixed wing models must make the throttle go to zero, and in most
cases this is a wise choice.
To enable Pre-set failsafe, the receiver must be re-bound. After the receiver has finished initializing, but
with the bind plug still in place, the transmitter sticks and switches are moved to the desired mode or
positions. A brief press (<1S) on the button will set failsafe, as indicated by the Indicator 1 Green light. If
you get a blue light you have held the button down too long and have entered Always-ON mode. Hold it
down again till the blue LED goes out.
The failsafe setting is stored and will not change until you deliberately do so. Even if you rebind the
receiver, the previously stored Pre-set values of failsafe are retained. Be very careful if you shift the
receiver to a different model that you cancel any Pre-set failsafe and reset appropriately.
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Lemon Stabilizer PLUS Receiver – Reference Guide
Understanding the Three Different “Calibrations"
Calibration of the gyros themselves
The gyros are very stable but over time they will gradually drift. Eventually there will be a significant
offset of the servo position when switching between Off and Rate stabilization. For this reason the
StabPLUS is designed so that it tries to calibrate the gyros internally every time when it is powered on.16
The first thing it does after power on, or after binding completes if the bind plug is in place, is to attempt
this gyro calibration. Unsuccessful calibration is normally due to movement during the 1-2 second
window before the blue/green Indicator 1 is flashing. Because of the stability of the circuits, unsuccessful
calibration is not normally an issue but after a few months it will need to be calibrated at some point.
Over a period of a few months of flying a particular plane it is expected there will be at least one chance
that the calibration will be made successfully because the plane is sufficiently stationary. However for
the worst-case scenario, if you are in the habit of moving planes during the initial power on when you
plug in the flight pack, then the gyro will never have a chance to calibrate. So it is recommended to
ensure a deliberate gyro calibration at power on with absolutely no movement of the plane during start
up every now and then. If you make a practice of always leaving the model stationary during the 1-2
second startup window, the problem will never arise.
Calibration of level attitude
This happens after gyro calibration.
A) If you do nothing to a stabilizer that has just been rebound, the stabilizer calibrates itself to make the
current bottom face of the case level with the ground regardless of the orientation or angle it is mounted
at and assumes 0 degree installation offset. If you switch to Autolevel in flight, the stabilizer will act on
the control surfaces to level itself. If the stabilizer is carefully installed with its fore/aft axis along the level
flight direction of the plane this may work perfectly well.
B) However you may find that the plane does not fly level enough because the stabilizer is not exactly
along the axes or the plane requires some up or down angle to fly level. You also have to perform the
following if it is not mounted in the default flat and level orientation. If during the 9 seconds that the
green/blue Indicator 1 LEDs are flashing you do a toggle, then the stabilizer makes the calibration with
respect to the plane. That is - the position the plane is in becomes “level flight”. If you switch to Autolevel in flight, the stabilizer will act on the control surfaces to level the plane. It also sets the orientation
memory. During this calibration Indicator 2 stays red.
At the end of the 9 second window, Indicator 2 close to the header pins will show 4 green flashes if
calibration was successful or red flashes if calibration is not achieved. The red flash is normally due to a
huge movement during the calibration period or a stabilizer that is mounted at an extreme angle and
you need to repeat the process. If the stabilizer exceeds its detectable range with an installation offset of
more than 20 degree from level, this will cause failure of this calibration. Do not leave the ground if you
do a toggle and the green Indicator flash is not achieved! NOTE that the offset correction is saved when
power is removed.
It is not necessary to do a level calibration by toggling every time you power up the stabilizer. If you do
not, then the previous leveling and stabilizer orientation (upright/inverted/sideways) will be used.
16
The automatic mechanism of the StabPLUS contrasts with the manual process used by the regular Lemon
Stabilizer, involving opening the case (v.3) or using two bind plugs (v.4 and 4.5).
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Lemon Stabilizer PLUS Receiver – Reference Guide
Calibration for trim offset
This applies a correction of any trims to neutral for the stabilizer so it doesn't think trim is an actual stick
deflection. This is done with a toggle at any time after the first 9 seconds when the receiver is receiving a
transmitted signal and is able to control the servos. It is saved when power is removed so does not have
to be done again for that model if you do not change flight trim.
Why the Gyros Need Occasional Recalibration
The stabilizer senses motion through tiny solid state gyros and accelerometers. The gyros perform the
same function as the old fashioned spinning wheel gyroscopes: they resist any attempt to move them
and the force of the resulting resistance can be measured, amplified and used to control the servos.
Instead of a spinning mechanical wheel, the MPU-3050 Motion Processing Unit sensor in the StabPLUS
uses tiny solid state elements that vibrate about 30,000 times a second. The gyros can sense an angular
rate of up to +/-2000˚/sec for a full range output. They are so small that they can withstand a shock of
10,000g! They are extremely accurate and stable. Over a long time however the circuits in the MPU can
drift and it is sensible to recalibrate them occasionally.
Unlike with the original Lemon stabilizer, the user no longer needs to manually perform gyro calibration.
This is done automatically during power on and the whole process takes about 1.2 seconds. If no
vibration is detected during power on, the gyro offset value will be automatically updated, indicated by
the green LED in Indicator 2 flashing twice.
If vibration is detected during power on, the stored calibration value will be used. This will be signaled by
the red LED flashing twice.
What the LEDs Mean
The StabPLUS has three sets of LEDs: Indicator 1, the blue/green ones near the pushbutton, Indicator 2,
the red/green ones on the top near the connectors, and a red one on the back of the PC board, inside
the case. This single internal LED can normally be ignored as it is basically just to show that the receiver
is connected to the transmitter. There is one exception: when using a transmitter on DSM2 this LED can
flash a “brownout warning” to indicate momentary power loss.
Basic Light Signals – Indicator 2 and Internal Lights
Status
LEDs
Transmitter
Normal Operation
Receiver
Stabilizer
Green LED
Red LED
OFF
ON
-
X
ON
ON
ON
ON
ON
ON
OFF
Autolevel
Gyro
✓
✓
X
DSM2 only
“Brownout”17
–
–
ON
Rapid Flash
Flashing
✓
Rapid Flash
Flashing
✓
Internal LED
X
X
✓
✓
✓
✓
Flashing
Alternating
Binding
–
BIND MODE
BIND MODE
BIND MODE
BINDING
BOUND
Rapid Flash
Slow Flash
✓
17
The “Brownout warning” will be triggered if you turn a DSM2 receiver off and back on again without also power
cycling the transmitter.
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Lemon Stabilizer PLUS Receiver – Reference Guide
Bottom line:
A properly bound, active stabilizer in Rate (Gyro) mode will show a solid Green external LED.
In Autolevel mode the alternating Green and Red LEDs will show.
Both LEDs will come on when you turn the stabilizer OFF using the gear channel or the DIP switches.
Other Light Signals – Indicator 1 and 2 Lights
Function
Stick Centring (toggle after initialization)
Pre-set Failsafe ON
Stabilizer Always-ON
Gyro calibration: 1st second of power cycle
LED Indications
Mode Red/Green rapid flash very briefly
Indicator 1: Green ON
No light indicates No-Pulse failsafe
Indicator 1: Blue ON
Mode indicator: Green flashes twice = OK
Red flashes twice = fail.
Awaiting toggle for pitch/roll/stabilizer
orientation calibration – after power cycle
and gyro calibration (max. wait = ~9sec)
Indicator 1: Green/Blue slow flashing
Accepted toggle.
Calibration in progress for pitch/ roll/
stabilizer orientation
Mode indicator: Red ON for ~4 seconds,
followed by green flashes for successful
calibration, red flashes for fail
Further Options
Stabilizer Always-ON
During the bind process you can set the stabilizer to be permanently on.
Set the three-position switch for Autolevel (Indicator 2 Red/Green LED alternating) or Gyro mode
(Indicator 2 Green LED ON) as desired.
Press and hold the button until Indicator 1 blue LED is on. Blue LED on means the stabilizer is always on
in either auto-level or gyro mode. Channel 5 will no longer have any effect on stabilizer mode and is
available for retracts or similar. You should choose whether you want Gyro or Auto level mode using the
channel 5 switch before you select Always-on (since you cannot then change it). However the toggle
gesture for both Orientation/Autolevel offset and Trim offset will still work in Always-on mode.
Remove bind plug and power cycle the unit.
If a suitable transmitter is used, Master Gain on channel 8 can be used to effectively turn OFF the
stabilizer if required.
To set a transmitter with only a two-position switch on channel 5 (Gear) to Always-ON, you first need to
ensure that Mode Order is set correctly. For Gyro mode Always-ON, select OFF/AL/Gyro as the order; for
Autolevel select OFF/Gyro/AL as the order.
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Lemon Stabilizer PLUS Receiver – Reference Guide
Hardware Reset
To reset the StabPLUS to factory default settings, insert a bind plug on the signal pins of channels
2, 3, and 4, as shown in the picture. Note that channel 2 (Aileron) is the third set of pins from the left.
The ESC, BEC or battery is connected to channel 1 (Throttle) as usual (or to other available channel pins).
The transmitter is not required.
When power is applied briefly, the lights on the receiver will blink in
sequence, indicating that all internal settings have been returned to
default. This includes any stabilizer offsets, orientation settings,
failsafe presets, mode order changes, etc.
To complete the reset, you may wish to set the stabilizer pots back to
the 12 o’clock position and return all DIP switches to OFF, but this is
not required.
A good practice if you encounter unexpected behavior from the
stabilizer is to perform a hardware reset, followed by rebinding of
the receiver. Then start afresh with stabilizer settings.
Mixing
Mixing and the Lemon Stabilized Receiver
The Essential Instructions should give you the information you need to set up elevon or V-tail mixing
with the Lemon StabPLUS. The purpose of this section is to explain further how all this works. This
section does not apply if DIP switches 4 and 5 are off as the StabPLUS then operates exactly like a normal
7 channel unstabilized receiver and all mixing needs to be done at the transmitter.
The key point to understand is that the Lemon stabilizer only recognizes and corrects for movement in
the three standard flight axes (shown in the diagram on page 8). Consequently, the stabilizer expects the
transmitter to provide the conventional “pure” inputs: roll (aileron), pitch (elevator) and yaw (rudder).
Any processing (mixing) needed to turn these inputs into servo commands for a non-standard control
arrangement such as elevon or V-tail MUST take place in the stabilizer itself, NOT in the transmitter. By
contrast, even when stabilization is active, flaperon and other types of mixing take place in the
transmitter.
What is mixing?
In a simple control setup, each axis has a dedicated control surface (or pair of surfaces in the case of
aileron). Each axis is controlled by a separate channel passed from the transmitter through the receiver
(and its integrated stabilizer) and onward to the servo that moves the control surface. For the Lemon
receivers, channels 2, 3 and 4 are used, respectively, for the three basic flight surface controls, aileron,
elevator and rudder.
Mixing is the process of combining transmitter inputs to provide the servo output(s) required for control.
For many purposes, the mixing is done in the transmitter. For example, throttle can be mixed to elevator
so that as power is increased, a small amount of down is added to the elevator signal in order to counter
the model’s tendency to climb. Another common mix couples aileron and rudder to aid in coordinating
turns. The important thing about such mixes for our purposes is that they don’t affect the basic
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Lemon Stabilizer PLUS Receiver – Reference Guide
arrangement of allocating one channel to each control axis or function. Consequently, they still provide
the separate inputs required by the stabilizer.
However they DO affect behavior in Autolevel mode since Autolevel reacts to any change in the position
of the aileron and elevator channels as a command to change the attitude of the plane and a
Throttle->Elevator mix for example will do just that.
The V-tail and elevon mixes we are concerned with here are different in that they involve two separate
and independently driven control surfaces working together to provide a single aerodynamic function.
For example, a pair of elevons must work in unison to produce pitch and in opposition to generate roll.
To achieve this, the mixing MUST be done on board, since the stabilizer cannot interpret inputs in the
form of “mixed” control commands; it only understands roll, pitch and yaw. Any V-tail or elevon mixing in
the transmitter must therefore be disabled.
Flaperon is another case where two inputs (aileron and flap) are involved, but only one is a primary flight
control, so here the mixing is done in the transmitter.
Let’s take a look specifically at how these three types of control setup are dealt with in relation to the
Lemon StabPLUS. DIP switches are the six small white slide switches on the receiver, which are
numbered and referred to by Lemon as J1 to J6.
V Tail
In this arrangement, the functions of elevator and rudder are managed by tail control surfaces that move
up or down together for pitch, right or left together for yaw. Right rudder is achieved by the left surface
moving UP and the right surface moving DOWN.
In the transmitter tail type (if available) is set to Normal (not V-tail); this ensures that separate (not
mixed) elevator and rudder signals are sent to the stabilizer. In the receiver, DIP switch J4 (Delta) is OFF
and DIP switch J5 (V-tail) is ON, thus activating on-board mixing. The setting of DIP switch J6 depends on
the aileron configuration. The right and left tail servos are normally plugged into channels 3 (elevator)
and 4 (rudder) respectively.
Elevon / Delta Wing
This arrangement is generally used for a tailless aircraft, such as a flying wing or delta, in which the wing
control surfaces (elevons) are used to control both pitch (elevator) and roll (aileron). The elevons move
up or down together for pitch and in opposite directions for roll. Right roll is achieved by the left elevon
moving DOWN and the right elevon moving UP.
In the transmitter, Wing Type is set to Normal (not Delta). In the receiver, DIP switch J4 (Delta) is ON to
activate mixing. DIP switches J5 (V-tail) and J6 (flaperon) are OFF. The right and left elevon servos are
conventionally plugged into channels 2 (aileron) and 3 (elevator) respectively, but it is often necessary to
interchange the servo connections to achieve correct control directions.
Flaperons (dual aileron servos on separate channels)
The flaperon arrangement enables the ailerons not only to move in the usual opposite directions to
produce roll, but also to move together downward to produce flap action (and possibly upward to
produce spoiler action), thus controlling lift and drag.
This dual function capability requires that each aileron servo have its own channel: normally channel 2
for right aileron (RAil) and channel 6 for left aileron (LAil). The stabilizer (with J6 ON) passes the control
inputs sent by the transmitter through to the two aileron channels. The inputs can include not only
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Lemon Stabilizer PLUS Receiver – Reference Guide
flaperon mixing but also differential aileron (more up than down to compensate for adverse aileron drag).
Unlike V-tail and Elevon, where the mixing happens in the stabilizer, aileron/flaperon mixing takes place
in the transmitter.
For the stabilizer to apply corrections to both ailerons in response to wind gusts, etc., switch J6 must be
ON. (If it is OFF, only the right aileron (CH2) will have stabilizer action.)
In the transmitter, Wing Type should be set to Flaperon, as appropriate. If flaperon is used, then Flap
mixing may be applied; this usually includes mixing to the elevator channel to compensate for the pitch
effects of flap action. Also, differential aileron can be applied if required.
In the receiver, DIP switch J6 (flaperon) is ON to enable stabilization on the second aileron channel. DIP
switches J4 and J5 are ON (except for a model with a V-tail, when J4 must be OFF). The right and left
aileron servos are plugged into channels 2 and 6 respectively.
NOTE: You MUST NOT use either Flaperons or Aileron Differential when Auto level mode is active; see
the warning below.
Reversing Control and Stabilization Directions with Mixing
After setting any mixing is set up for V-Tail, Elevons and Flaperons, the direction of response of the
control surfaces to the transmitter inputs must be checked and corrected as necessary. To avoid
distracting control surface motions, stabilizer action should be turned OFF with the Mode switch
(channel 5/Gear) during this process (mixing is not affected by turning off the mode switch).
Note that to achieve the correct control directions, it may be necessary not only to use channel reversing
in the transmitter but also to interchange the plugs of the two servos involved in the control mixing. For
example, if both V-tail surfaces move sideways when the elevator stick is moved, interchange the plugs in
channels 3 and 4. Then if necessary, use channel reverse in the transmitter to adjust the direction of
motion of the two surfaces.
When all control settings and mixing are completed, and the control directions are correct, the direction
of the stabilizer’s response to a flight disturbance must be set for each axis. Checking must be done
with the stabilizer turned ON and in accordance with the instructions provided earlier (see page 7). To
change the direction of response for an axis, use the appropriate DIP switch: J1 (aileron), J2 (elevator) or
J3 (rudder).
WARNING: Flaperons and Aileron Differential
Autolevel mode on the StabPLUS is intended to help you stay within safe limits or recover from difficult
situations. This means, however, that it must limit the pilot's degree of control and restrict certain
options.
In particular, Autolevel is incompatible with the use of either Flaperons or Aileron Differential. These
advanced features, found on most programmable Spektrum transmitters, are only available when dual
aileron servos are driven by separate channels. Here’s why they can't be used with Autolevel:
When activated, the flaperon function causes the servos to lower or raise both ailerons, thus giving a
flap or spoiler effect. This action represents a significant shift in the neutral settings of the two aileron
channels. The stabilizer, however, in Autolevel mode may interpret this shift as a command to roll the
model. Thus, selecting Autolevel while flaperons are deployed may cause the model to bank or even roll
inverted. Hence, flaperons must NOT be deployed when the stabilizer is in Autolevel mode.
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Lemon Stabilizer PLUS Receiver – Reference Guide
Likewise, Aileron Differential causes the two servos to travel different amounts. For example, in a right
turn, positive differential will cause the right aileron to go UP more than the left aileron goes DOWN.
This can conflict with the efforts of Autolevel to apply roll correction.
Consequently, the message is: Don't use either Flaperons or Aileron Differential while the StabPLUS is
in Autolevel mode.
Solutions
Flaperons can be used when the StabPLUS is in OFF or Gyro mode, but be sure you don’t accidentally
select Autolevel at the same time. The safest approach is to disable either flaperons or Autolevel. There’s
no problem using two servos on separate channels in Dual Aileron Wing Type, or a Y-cable to drive both
servos off the Aileron channel in Normal Wing Type. It’s when the Wing Type is set to Flaperons that you
need to take great care.
If you do choose to use flaperons with the StabPLUS, we have on RCGroups provided mixes for the DX8
and for more recent Spektrum transmitters that ensure that Autolevel mode can’t be selected when
flaperons are active. For details on these mixes, go to Post #4 of The Official Lemon Instructions thread:
https://www.rcgroups.com/forums/showpost.php?p=29478801&postcount=4
Although the way Autolevel mode works in the Lemon StabPLUS is not compatible with Aileron
Differential, you might want to program your transmitter to allow use of differential when the Stabilizer
is set to OFF or Gyro mode. To do this in a modern Spektrum transmitter, use the same three-position
switch to select Differential as you use for Stabilizer Mode; simply ensure that the differential amount
corresponding to the Autolevel switch position is set to 0%.
In the default setup of the StabPLUS, Position 0 corresponds to OFF and Position 1 to Gyro mode. The
differential values for these positions can be set according to your preferences. The differential for
Position 0 (Autolevel) must, however, be set to 0%.
Note that even with differential set to 0%, Autolevel provides Gyro-type stabilization on the yaw axis,
thus helping to ensure coordinated turns. In addition, you might want to program your transmitter to
provide a small amount of aileron-to-rudder mixing, either full time or only when in in Autolevel mode.
Finally, “old-fashioned” mechanical aileron differential is very effective and is generally easy to
incorporate by offsetting either the servo arms or the aileron control horns.
Stabilizer Modes: Gyro vs. Autolevel
Although Gyro (Rate) and Autolevel both stabilize the model, they operate in quite different ways and
result in totally different control responses.
Gyro mode responds to a disturbance of the plane by giving a “pulse” of opposite control surface
movement. It works by sensing the angular motion18 about one or more of the three flight axes. If the
model is moving in a straight line with no change in direction, the stabilizer does nothing. But if a gust
hits the plane and lifts one wing, the stabilizer immediately applies opposite aileron to counteract the
roll. The aggressiveness of the response (the amount of aileron deflection) is determined by the gain on
the roll axis and the violence of the disturbance. That gain is a product of the setting of the stabilizer's
18
Technically, the Motion Processing Unit (MPU-3050) measures the angular rate in degrees/second, which is an
angular velocity, but it may be easier to think of the stabilizer reacting to an angular acceleration. Acceleration is
just the rate of change of velocity.
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Lemon Stabilizer PLUS Receiver – Reference Guide
Aileron pot (which has a value of 1 at midpoint) multiplied by the Master Gain value set by channel 8
(which is 1 if channel 8 is not available).19
If the gains on the three axes are correctly set, the effect is to “damp out” external disturbances caused
by turbulence due to wind, gusts and thermal activity. The stabilizer acts as though it has increased the
inertia of the plane. Many pilots describe Gyro mode as like flying a much bigger and steadier model.
However, if the gains are set too high, the stabilizer applies too much correction and the end result is an
oscillation back and forth rather than damping of the disturbance.
Autolevel mode works quite differently.
In this mode, if the inputs from the sticks
are neutral, the stabilizer constantly tries
to return itself to a level position. If it's
correctly installed and adjusted, and you
don't touch the sticks, it will try to keep
the model flying in a straight line with
wings level. Given a suitable throttle
setting, this results in more or less level
flight. This diagram we saw earlier shows
the three flight axes. In Autolevel mode,
with no stick input, the stabilizer keeps
the Z axis aligned with the downward
direction of gravity. So if the model
pitches up or down or rolls from side to side, the stabilizer will automatically correct by leveling the
model. If a gust hits the model, the stabilizer will immediately return the model to level attitude, no
matter the strength of the original disturbance. The stabilizer in this mode does not attempt to hold the
heading of the model, but simply applies Gyro (rate) stabilization to the rudder to damp out directional
disturbances in the yaw axis.
So what happens if you deflect a stick in Autolevel mode? The stabilizer adjusts the ailerons and/or
elevator to move the model away from level to a new bank/pitch attitude that is determined by the stick
deflection. As long as you hold the stick with a constant deflection, the stabilizer works to maintain that
attitude. As soon as you release the sticks to neutral, the stabilizer returns the model to level flight.
Of course, there is no exact correspondence between stick deflection and model’s attitude. The stick
commands a response which is proportional to its angle, but the proportionality varies with two main
factors.
First, the sticks on most transmitters are physically limited to between 30 and 40 degrees of deflection
on each side of neutral, but we want to have the option of commanding steeper angles of bank and pitch
for greater maneuverability. To this end, the Autolevel function of the stabilizer has two settings,
Beginner giving very restricted bank and pitch angles and Advanced allowing steeper angles and thus
greater maneuverability. As well, the servo travel volume (end point) settings of the transmitter for
aileron and elevator directly adjust the maximum angles that can be commanded.20
19
If there is no channel 8 on the transmitter, Master Gain defaults to a constant multiplier of 1.0x.
20
In addition, the gain settings on the stabilizer (and Master Gain, if available) will affect the ratio of stick-to-model
movement, up to the maximum limit. Hence, the maximum bank angle is slightly affected by the gain setting, and
there may be variation of a few degrees from the exact 30/45 or 50/75 numbers.
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Lemon Stabilizer PLUS Receiver – Reference Guide
To be specific, Autolevel Beginner mode limits the bank and pitch angles of the model to about 30°
maximum with the transmitter set to 100% servo throw. If you increase the servo throw to 150% in the
servo travel menu, the maximum bank/pitch angle will increase to about 45°. In Advanced mode, full
stick deflection produces a maximum bank/pitch angle of about 50° for 100% and 75° for 150% servo
limits.
To summarize how the Lemon StabPLUS in Autolevel mode functions:

Roll (aileron): Stick input directly controls the roll angle (bank) of the model. The roll angle is
proportional to the stick deflection.

Pitch (elevator): Stick input directly controls the pitch angle of the model. The pitch angle is
proportional to the stick deflection.

Yaw (rudder): Autolevel mode does not apply to the rudder channel. Instead when Autolevel is
selected, the rudder is stabilized in Gyro mode, reacting to angular disturbances while
responding to control inputs in the usual way.
The individual channel gains (and master gain if available) do NOT significantly affect the maximum bank
and pitch angles. However they do affect the speed with which the stabilizer responds and the ratio of
the response angle with respect to the stick deflection up to the maximum value. High gains will give
more rapid response and a greater model angle for a given stick deflection, up to the maximum available.
In roll and pitch, there may be a progressive movement with the model rapidly following the first
deflection then gradually reaching the final position.
The critical difference between Gyro mode and Autolevel mode.
Essentially a stabilizer in Gyro mode does not alter the way in which the control surfaces affect the flight
behavior of the model except to “damp” its reactions, particularly to external disturbances. The control
surfaces work exactly as they do in a real aircraft. If you push the stick to one side and hold it the plane
will roll and continue to do so until you neutralize the control. To roll out of the turn, you have to apply
opposite aileron. Gyro mode, like flying without stabilization, is as though you put yourself in the cockpit
and make the aircraft your frame of reference.
Autolevel stabilization on the other hand adjusts the plane’s orientation with respect to an absolute
“down” direction. If you deflect the stick by a certain amount and keep it there, the plane simply goes to
the commanded attitude and holds it.
With Autolevel it’s as though you are on the ground and the frame of reference is the earth. And that is
exactly how it is for RC pilots, as we are on the ground. For beginners in particular, Autolevel can be a
great help, giving them a chance to sort out their reactions and deal, for example, with apparently
reversed control directions when the model is flying toward them. This is vital for those who lack the
assistance of an instructor; as it can save the pilot from disorientation that too often result in a crash.
The more you fly and less you crash, the quicker you can become a good pilot. It also helps greatly during
landing, where you are trying to keep the model in a constant relationship with the ground. Autolevel is
also popular with FPV (first person view) pilots who let the stabilizer take control and fly the plane
straight and level while they concentrate on shooting an image.
Thus Autolevel mode is much like “steering” the plane around the sky. Let the sticks go and the model
will always attempt to return to flying straight and level.
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Lemon Stabilizer PLUS Receiver – Reference Guide
By contrast, Gyro stabilization does make the model easier to fly, but only in the sense that it smooths
out the response and helps the model resist disturbances. Gyro stabilization is very like normal
unstabilized RC flying but much smoother – particularly in windy conditions.
The stabilizer when in Gyro mode is designed to do its job while minimizing interference with normal
control. To achieve this, the amount of correction (stabilizer gain) is automatically reduced for large stick
excursions. This is because the stabilizer will see your large intended movement as a significant
disturbance and will attempt to correct it strongly. It only senses the model moving and does not know
whether it was an intended movement or an unintended one. The balance between onboard
stabilization and transmitter control is a compromise, as there is always some stabilizing effect whenever
the stabilizer is active. Consequently, for maximum response to stick inputs, you can set the Stabilizer
Mode switch to OFF.
In practice the Gyro mode does just what most people need most of the time – smoothing out flight
while leaving the pilot fully in control. Autolevel reduces control response, offering useful options but at
the expense of some degree of pilot control. In particular, Autolevel is good for beginners, or for FPV
pilots who want to concentrate on imaging, but it does restrict the flight envelope. The Beginner setting
in Autolevel is particularly restrictive, so if you want to improve your piloting skills you should move off it
as soon as you have the confidence. Experienced flight instructors generally encourage students to shift
to Autolevel Advanced mode and then to Gyro stabilization as early as possible so that they learn to
control the plane instinctively using normal surface deflections.
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Lemon Stabilizer PLUS Receiver – Reference Guide
Appendices
Appendix 1: Diversity and RSSI
The principles
There is quite a bit of confusion about the purpose and significance of diversity antennas and the
meaning of Received Signal Strength Indication (RSSI).21 Some of this is compounded by “expert” advice
from modelers who grew up in the era of dedicated frequency AM or FM receivers who may not be
familiar with modern 2.4GHz Spread Spectrum R/C systems such as DSMX.
All common RF control systems work by propagating a high frequency electromagnetic signal from a
transmitter to a receiver. If the transmitter antenna is reasonably well tuned to the frequency of the
signal, an electromagnetic wave is generated that can propagate through space to generate matching
voltage variations in an antenna connected to a sensitive receiver. This is the fundamental basis of all
common RF communication.
One simple way to measure the “strength” of the signal is to measure the voltage appearing at some
point near the antenna in the receiver. Some popular RC systems including FrSky and the Lemon
telemetry systems, display an RSSI value (Received Signal Strength Indication). The RSSI used in model
control systems may vary between systems and according to how it is measured. Nevertheless, for a
given system, RSSI is a useful measure of the signal received at your model. We’ll refer to this as Signal
Strength.
However, what really matters is not the absolute signal strength but the signal/noise ratio. Optimizing
the signal/noise ratio and minimizing any interference from other sources or multipath reception is
important for signal integrity – but there’s more to 2.4GHz spread spectrum radio than this. Our 2.4 RC
signal is not an analog modulated RF carrier signal but a digitally encoded one. And it is spread across
the frequency band not concentrated at a single frequency. In a spread spectrum system, a pseudorandom number (PN) sequence is used to randomize the signal in the air. Only the receiver having the
exact same pseudo-random sequence and synchronous timing can decode and retrieve the original
signal.
Because the control data is encoded into digital numbers and transmitted over a range of frequencies
“spread” over the 2.4 GHz band, then as far as the receiver is concerned the correct data is either there
or it is not – there is no half-way house of a “poor” signal. The receiver does not rely solely on the
strength of the transmitted signal (although that is still important) but on its ability to recognize the
correct encoded data from the accumulation of signals it sees. It is perfectly normal for the strength of a
particular signal to be less than the noise level on the band yet for an unambiguous data stream to be
detected.
As one expert described it, “It's like hearing a whisper at a heavy metal concert”. A good analogy is
conversation at a fairly rowdy party. Imagine you and your partner are having an intimate conversation.
When you are standing face to face you can each make out every word. But if you start moving further
and further apart, communication becomes more difficult. When you get to a certain distance, you have
to face the other person and concentrate intently on what they are saying in order to avoid serious
21
The StabPLUS does not display an RSSI value on the transmitter as it does not support telemetry. However the
term is commonly used to describe the actual signal strength at the receiver.
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misunderstandings. In radio terms your antennas have to be optimally aligned for maximum signal
transfer and maximum noise rejection. No matter how hard you try to concentrate, as you move still
farther apart the surrounding babble eventually overwhelms any attempt to understand your partner
and everything becomes unintelligible. The signal gets lost in the noise. However what if you and your
partner are the only English speakers at a noisy party of Mandarin-speaking Chinese? You will be able to
understand your partner at a greater distance this time because you are the only two in the room with a
particular data encoding system (English) while the background noise uses a different system (Mandarin).
This is so even though everyone is using the same medium, audio speech. With different coding, you can
separate the meaningful conversation from meaningless background even if the background is louder.
Only a receiver able to properly decode the transmitted signal gets a clear data stream with
unambiguous information. The various proprietary systems used in RC (DSM2 and DSMX are just two
examples) all work on the same principle, varying in the way the frequencies are used and distributed.
Let’s call this Data Integrity. Data integrity is important because in digital systems what finally matters is
simply whether a valid data packet is received or not.
Different systems have their own ways of reporting on signal strength and data integrity. Spektrum
systems do not report an RSSI value at all. They use three different measures of data integrity. Firstly,
antenna fades (A). These apply to a specific antenna and represent the loss of a small chunk of
information. They are often fairly frequent – it’s normal to have as many as 50 – 100 antenna fades on
any one of the antennas during a flight. This is a measure of signal strength, which contributes to data
integrity.
Secondly the system reports on frame loss (F). This means simultaneous antenna fades on all attached
receivers. It represents the loss of a valid data frame, so is a measure of data integrity. If the RF link is
performing optimally, frame losses per flight should be less than 20.
Finally they will report on holds (H) – a hold occurs when 45 contiguous (one right after the other) frame
losses occur. This is a serious loss of data frames over an extended period of about one second. Any
holds are a matter of concern.
Lemon systems do not report on any of these three values but all of the above helps define what we are
striving for and to understand what we need to do to optimize the control link. The reporting of RSSI is
only an indication of the reliability of the signal link. In the end it is data integrity that is the critical thing.
In a sense the receiver doesn’t care about how the signal got there, only if the data is accurate and
uncorrupted. We need to maximize the RF transmission link between transmitter and receiver AND
ensure the receiver receives a continuous flow of valid data packets. We maximize the signal strength by
optimizing the location and direction of an antenna. This provides the “best” or strongest signal between
the transmitter and receiver.
We optimize the likelihood of receiving valid data packets by adding “diversity” switching to the antenna
system, ensuring that the receiver has multiple sources of data. With a diversity switch, the encoding
“match” between the transmitter and receiver allows the receiver to only hear the data it's looking for. If
it doesn’t see it, then it will use the other antenna – although the precise logic behind the antenna
switching algorithm is generally a proprietary secret of the vendor. (Some Lemon receivers achieve
diversity by adding a satellite receiver to provide another data source, and some can use both a satellite
and dual diversity antennas, for a total of up to four data sources.)
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It is important to emphasize that the receiver does not look for the “best” or strongest signal among
those available to it. Data is either valid or not and the receiver simply looks for a data from a valid
source. Any one will do and no special decision is needed.
With our RC systems we do not attempt to measure the error rate and correct any errors; there are not
enough extra bits sent to unscramble a faulty reception. We just wait, since we are sending it again
shortly. Statistically, it's likely to arrive just fine the next time. If it doesn't, there's always another in just
a few milliseconds.
The Practical Implications
Lemon receivers including the StabPLUS are all described as full range. While absolute or theoretical
range is not affected by the use of dual antennas (or satellite receivers), adding diversity should help to
ensure that there is always at least one antenna capable of delivering data within that range. Of course,
this assumes that the installation is done correctly, and that the antennas are placed in favorable
locations, with the active portions well separated and in different alignments.
The “diversity” StabPLUS has two active antenna wires (the last 32mm with outer sheath stripped off)
connected to a switch that selects between them. Commonly you will see this described as “selecting the
stronger available signal” but this is not strictly true. The receiver will continue to use one antenna as
long as valid data is being received. If valid data packets cease it will switch antennas very quickly and
use the other. The switch will occur within 300mS and no control signal is lost during the switching
period.
Some receivers (including many Lemon standard receivers and the original Stabilizer which is still sold)
also have a connector to allow the use of a satellite for additional signal robustness. A satellite does not
increase the maximum possible range. Rather, as a separate stand-alone receiver it increases the
probability that a reliable signal will be obtained no matter the orientation of the model. The satellite
may also have a diversity twin antenna system identical to the receiver. The main receiver will read its
own data and that from the satellite. It doesn’t care where it comes from since the data signals are
identical. As long as one is there it will function correctly. Note that if the satellite has diversity antennas
there are four separate antenna sources for the receiver/satellite combination. The effect is that the
receiver may be using data received by any one of them depending on the orientation of the model.
The antennas we use for radio control radiate (and receive) in all directions, but the signal is much
weaker off the ends of the antenna (the active portion of the cable) than "broadside" to it. Think of an
ancient naval battle where the ships had very little firepower fore and aft because most of their cannon
were pointed out the sides.
To achieve the most reliable possible link to the model, therefore, what we want to avoid are situations
in which the transmitter and receiver antennas are end-on to each other. For the transmitter, the advice
to the pilot is simple: don't point the antenna at the model. For the receiver, things are more
complicated because the model is constantly changing its orientation in relation to the transmitter. A
single receiver antenna will inevitably be pointed at the transmitter some of the time.
This is where diversity comes in. If the receiver has two active antennas positioned at right angles to
each other, they can never both be pointed at the transmitter simultaneously. The receiver has an
excellent chance that valid data will be available from at least one of the two.
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Diversity improves the reliability of the RF link in other ways. If the two receiver antennas are well
separated, at least one should have a clear view of the transmitter, minimizing the risk of signal blanking.
As well, with antennas at right angles one of them should be roughly parallel to the transmitter antenna,
thus aligning polarization for a stronger signal.
Conductive materials such as foil coverings, batteries, metal components and carbon fiber can absorb
and shield the incoming radio signal. 2.4GHz systems have a very short wave length and are susceptible
to this. Receiver aerials need to be placed so that this effect is minimized.
What all this means for the installation of the receiver is simple. Make sure its antenna is not close to
conductive stuff like battery, wiring and carbon fiber. If it has twin antenna, ensure the two antennas are
separated as far as practical from each other and keep the active portions (the last 30mm/1.2 inches or
so) reasonably straight and at right angles to each other.
In a case where the model has a large flat
conductive area, such as carbon fiber or metallic
covering. The antenna should be then mounted
perpendicular to the conductive surface.
To avoid an unwanted reflection/coupling effect,
never place the antenna close and parallel to any
wire or conducting surface. This is even more
important than the angle between the two
diversity antennas.
Just think of the signal as a “light ray” and the
conductive object as a “mirror”.
Types of Lemon antenna
The correct length for the short simple wire 2.4GHz antenna found on the single antenna version of the
StabPLUS is 29mm. This is slightly shorter than theoretical ¼ wavelength of 31.25mm due to the coupling
effect for an omnidirectional ¼ wave antenna. Note that the actual length can vary a bit for other brand
receivers, which may be as short as 27mm.
The dual diversity antenna versions have slightly longer active ends due to attenuation by the coax cable
portion. When positioning the antenna, it is the thin exposed active end that is critical.
Last word
Don't get paranoid. The installation doesn't have to be perfect to support an adequately strong RF link.
Our modern receivers do a remarkably good job of picking up the signal, even with just a simple single
antenna, so diversity can be thought of as extra security for when the going gets tough.
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Appendix 2: Range Checking
To verify a new installation or to check radio operation before the first flight of the day, use the Range
Test function on your transmitter. This temporarily attenuates transmitter power, reducing range by a
factor of about 30. With Spektrum transmitters, full control at “30 paces” in Range Test mode indicates
ample range for normal visual flying (the distance is now specified as 30m or about 33yds). Normally the
receiver will show considerably more range than this, but the important thing for safe flying is that it
meet this basic go/no go standard.
Range varies with the square of output power. To double the range, the transmitter requires four times
the power(2 squared). This explains the large reduction in power needed for the Range Test. The power
is cut not by 30X but by 30X squared, or a factor of about 900. So if the transmitter puts out 100mw
(milliwatts) at full power, in range check mode its output is cut to a little over 0.1mw.
There are two kinds of range test you should do: one-time testing of a new installation to discover any
problems of antenna location, etc. and routine checks at the beginning of each flying session to verify
that everything is working correctly. The first needs to be thorough, but the second can be very quick.
The key point about testing is that range is not an absolute value for a given receiver but can vary
considerably, depending on such factors as the alignment of the transmitter and receiver antennas,
whether the receiver antennas are blocked (“shadowed”) from some directions by the battery or other
conductive parts of the model, and proximity to the ground or metal objects like cars and trucks. Your
aim in initial testing is to ensure that not only is there satisfactory range in one direction, but that there
are no “dead spots” or directions in which range is considerably reduced.
What you do is to set up the model off the ground on a wooden stand in the middle of an open area.
Then, with the transmitter in range test mode, go out about 30m and walk around the model, moving
one of the controls deliberately, every second or two. What you’re looking for is loss of control on the
channel you are moving (or any sign of twitching on the controls that should be steady). While doing this,
deliberately keep the end of the transmitter antenna pointed at the model to ensure a worst case
scenario (not necessary for recent Spektrum transmitters with dual diversity antennas).
You should get no indication of signal loss at any point in your circumnavigation of the model at 30m. If
you do, it’s time to take a close look at the installation. If you have a single antenna StabPLUS, ask
yourself whether the antenna is clear of wiring, ESC, battery, etc. Often the best way to mount such a
receiver is against the fuselage side with the antenna poking out. With a dual diversity receiver, the tips
of the antennas should be well separated and at 90 degrees, and again not blocked by conductive stuff.
Rearrange the installation and try again until you get essentially no signal loss. This is normally not
difficult to achieve, but occasionally you’ll discover a problem and thereby prevent an accident.
You may want to continue out in one direction, still in range test mode, to find out what sort of range
your transmitter/receiver combination can achieve. Don’t be surprised if you get 50 to 100m or more.
But the important thing is reliable performance at 30m, which translates to nearly 1km at full power.
The purpose of a routine range test when you arrive at the field is simply to establish that things are
working properly. For example, a common failure mode is for the transmitter antenna cable to be
damaged, drastically reducing output, or for the receiver to suffer damage in a crash.
For the test, just go out 30m, switch to Range Test mode, and move one control repeatedly so you can
see that it’s responding properly. That’s enough to tell you that the RF link is functioning correctly.
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Appendix 3: Versions of the Lemon StabPLUS Receiver
Version 1 of the Lemon Stabilizer PLUS shipped in early January 2017.
Visually, the Stabilizer PLUS is very similar to its predecessor, the Lemon Stabilizer. It is packaged in the
same case, as the photos show. Identifying features include a push button for setting options (including
failsafe) and an additional pair of LED indicator lights. The PLUS can also be distinguished by the lack of a
satellite receiver connector. The obvious differences are highlighted in yellow in the photos.
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Appendix 4: Using the StabPLUS with a DX6i
The Spektrum DX6i is no longer available, but as one of the most popular transmitters of recent years
there are still vast numbers of them in use. The DX6i has a two-position switch on channel 5 (Gear/FMode), another two-position switch on channel 6 (Flap/Gyro) and two programmable mixes.
The Gear switch, a programmable mix and a second switch (such as Mix), can be used to simulate a
three-position switch:
MIX 1
GEAR →GEAR ACT
RATE D 0% U –100%
SW MIX TRIM INH
With GEAR channel set to Reverse (change N to R), this mix will produce -100%/0%/100% output,
functioning as follows:
 Gear switch in Position 0:
o Gives Stabilization OFF (100%) for either position of the Mix switch.
 Gear switch in Position 1:
o Mix switch in Position 0 gives Autolevel mode (-100%).
o Mix switch in Position 1 gives Gyro mode (0%)
The same mix but with GEAR channel to set to Normal will produce the following:

Gear switch in Position 0:
o Gives Autolevel (-100%) for either position of the Mix switch

Gear switch in Position 1:
o Mix switch in Position 0 gives OFF (100%).
o Mix switch in Position 1 gives Gyro mode (0%)
Your choice. Do you want quick access to OFF or Autolevel?
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Appendix 5: Using an Open Source Transmitter (Taranis, 9XR, etc.)
The Lemon stabilized receiver can be used with a transmitter other than Spektrum, provided it has a
DSMX or DSM2 compatible module installed that works correctly with the StabPLUS – not all do.
Transmitters such as the FrSky Taranis, Turnigy 9XR/9XR Pro, and FlySky/Turnigy 9x with ER9x all use
open source firmware that can be easily programmed to emulate the output of a Spektrum transmitter,
including such functions as flaperon mixing. While the programming steps are slightly different for the
various transmitters, the following generic setup can be applied to any of them:

Channels 1-4 set up as a simple four channel model with channel order TAER

Channel 5 set up to give -100%/0%/100% in response to a suitable three-position switch.

Channel 6 is available for dual aileron, flaps or gear, as required.

Channel 7 is available for flaps or gear, as required.

Channel 8 set up to provide +/- 100% in response to a knob, slider or lever.

Limits of 80% set on all channels to match Spektrum 100% pulse width.

Channel 2 (aileron) and channel 4 (rudder) reversed (inverted) to match Spektrum directions.
This will give you a transmitter that works very much like a DX8 and that provides a good basis for setting
up the stabilizer according to the Essential Instructions.
Pulse Widths and Percentage Travel
Pulse uS
860
Spektrum
OpenTX
900
988
-150%
-125%
1000
1100
1500
1900
2000
-125%
-100%
0%
100%
125%
-80%
0%
80%
-100%
Spektrum
1% = 4uS pulse width change
OpenTX
1% = 5.12uS pulse width change
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2100
2140
150%
100%
125%
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Appendix 6: Throttle “Drift” in Autolevel Mode
Why do the elevator and aileron settings “drift” in Autolevel mode when I apply throttle?
If you are testing the StabPLUS in Autolevel mode on the bench and displace the model from level, then
the control surfaces will deflect as the stabilizer attempts to bring it back to level. With throttle at low,
the deflection will simply remain until such time as you move the model back to the level position. If you
apply more than 25% throttle during displacement, however, the control surfaces will start to drift slowly
towards increasing deflection. Why is this so, when we know that the StabPLUS is not directly linked to
the throttle in any way?
The answer is that the stabilizer is smart enough to monitor the throttle and to modify its Autolevel
behavior if the setting is above 25%.
To understand what’s going on, pretend you are the StabPLUS and you’re flying the model at medium
throttle in Autolevel mode. The boss on the ground (the pilot) is letting you to do your “autopiloting” job
(i.e., is leaving the sticks in neutral).
Let’s say you notice that rather than staying level, the model is climbing. It’s time for you as the
“autopilot” to apply a little down elevator. After a second, you see that the model is still climbing, so you
add a bit more down, and so on till the model is finally back to level flight. You apply such a correction,
up or down, only when the throttle is above 25%, which you take to mean that the model is flying at
significant speed.
When the pilot throttles back below 25%, you, as autopilot, assume that the model is about to land and
that a correction is no longer needed. You might be tempted to pull back more and more on the elevator
in an attempt to maintain a level attitude, but because of the low throttle setting you allow the nose to
drop slightly, simply holding the normal amount of up elevator associated with the gliding state.
This “progressive amplifier” effect is applied to both pitch and roll axes, so produces on the bench what
looks like drift of both elevator and ailerons. It is purely an artifact of ground testing, however. If the
model is held stationary but one surface (say elevator) is deflected, the stabilizer keeps trying to add
more and more deflection in an effort to fix what it thinks is a non-response from the plane.
In the air this won’t happen because, given a reasonable amount of power, the model will respond and
keep doing so until the difference is zero (i.e., it’s flying in a level attitude). It’s not that there’s some kind
of mix or linkage between throttle and stabilization. Rather, the throttle setting is acting as a substitute
for airspeed. The StabPLUS assumes if the throttle is above 25% the model is flying “fast” and applies the
correction; below 25% it assumes the plane is flying “slow”, changes its behavior and cancels the
correction.
Technical Explanation
In technical terms, this means that the algorithm for trying to achieve level flight is different depending
whether the throttle is below or above 25%.
If the throttle is below 25%, the PID controller uses Proportional mode. The stabilizer responds with a
"P" correction directly proportional to the receiver’s angle of inclination; there is no integration with
respect to time.
If the throttle is above 25%, the PID controller mode is supplies both Proportional and Integrative
corrections. Accordingly, the servo moves progressively, integrating over time, to achieve the set point.
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The Practical Implications of this Behavior
As mmascari put it in a post on RCGroups, the basic assumption is that:
“If the throttle is over 25%, the plane must be moving with some decent control. Throttle below 25% and
the plane must be going slow.
“In both scenarios, the StabPLUS will give controls to cause the model to change attitude towards
normal…. The next step is, after those controls have been given, did the model actually change attitude
towards level?
“If the model is below 25% throttle, presumably moving slow, that's it, done, no further action is taken.
Say you're doing a slow landing, the model is pitched but not going all the way back to level from the
deflections made. Making the deflections farther isn't going to help at all, there's not enough speed for it
to cause the desired change. A bigger deflection is more likely to stall the plane instead or cause other
issues.
“If the model is above 25% throttle, presumably it's moving with some air speed, and if it hasn't changed
attitude in the desired direction, then additional deflection is made. For whatever reason the initial
deflection wasn't enough and so [the stabilizer] makes additional deflection to try and get [the plane] to
move in the correct direction.
“The throttle value of 25% is only used as a proxy for ‘is the plane moving through the air with some
speed’.… In the bench test, it turns out this is an incorrect proxy. The throttle can be above 25% but the
model still completely stationary. Additionally, in this bench test, the control deflections don't actually
change the attitude of the plane at all since the control surfaces have nothing to do with the attitude of
the model when it's only being held in your hand and not actually flying. If you move the model from
angled to level when you see the first deflection on the bench, you should see the deflections return to
neutral with no extra ramp up at all. Actually, moving towards level whenever should stop the extra
motion as it registers the attitude change.”
Bottom Line: The drift effect is perfectly normal and not something to worry about. Just one of the
behind-the-scenes things the stabilizer does to keep the model on track.
NOTICE
This manual is provided to help you understand and use the Lemon 7-Channel Stabilized Receiver PLUS. The authors
are not associated with Lemon Rx and this is not a Lemon Rx publication.
You can freely quote from, redistribute and/or modify this manual; in doing so please acknowledge the source and
any changes.
The manual is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
more details. In using this manual, you agree that you accept all responsibility.
For more information, see
http://www.rcgroups.com/forums/showthread.php?t=2164243
http://www.lemon-rx.com/shop/index.php?route=common/home
JJ604 and Daedalus66
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