Motorized Wheelchair Lift with Tilting Platform
By:
Jonathan de la Paz
Deborah Guttmann
Madeline Larkin
Team 1
Client Contact:
Dr. John D. Enderle
University of Connecticut
260 Glenbrook Rd, U-2157
Storrs, CT 06269
(860) 486-5521
Table of Contents:
TABLE OF CONTENTS
Abstract
IntroductionBackground
Preliminary Requirements and Limitations
Market Research
Methods –
Design 1
Design 2
Design 3
Discussion Optimal Design
Conclusion
Appendix A: Technical Specifications
Appendix B: Timeline
Appendix C: Budget and Parts List
Appendix D: Engineering Standards
Acknowledgments
References
3
4
4
6
7
13
17
36
40
41
42
43
44
45
46
2
Abstract:
The Motorized Wheelchair Lift with Tilting Platform is a fully motorized device
that helps persons confined to wheelchairs access all forms of modern health care. The
lift and tilting device are designed to be used during routine health care examinations, i.e.
dental checkups, physical examinations and diagnostic procedures such as mammograms.
This device is important to persons confined to wheelchairs as it helps position him/her
more easily during a health care procedure and it makes the patient more comfortable.
3
Introduction:
Background
Persons who are confined to wheelchairs need access to health care professionals
and diagnostic equipment. Unfortunately, this is not possible at all times due to the lack
of equipment available to properly raise and tilt a patient to the proper positioning.
Because this equipment is not readily available, it can be problematic for a patient
confined to a wheelchair to have an accurate mammogram or get a proper magnetic
resonance imaging (MRI) test. Eye exams, dental care, general physicals, and specialized
procedures such as MRIs and mammograms require patients to be in a certain position, at
a certain height, or to move the body in a certain way. In hospitals, most of the existing
devices for these procedures are not equipped to accommodate those in wheelchairs.
These persons with disabilities are unfairly faced with obstacles that do not limit
accessibility for others. Therefore, a platform device is ideal for this project to make it
possible for persons with disabilities to effortlessly access their healthcare procedures.
The major requirement for the device is two-degrees of freedom. Meaning that it will
have a vertical translation from three to nine inches and it will tilt to a full 10 degree
angle. A small ramp is required so the patient can easily wheel onto the platform. Also,
the device needs to be motorized and have a user interface that both the patient and the
healthcare practitioner will be able to use. The device is also required to be transportable
by means of rolling or carrying. On top of all the features that are required for the device,
safety features are also necessary.
Preliminary Requirements and Limitations
The Motorized Wheelchair Lift with Tilting Platform is designed to fully employ
all of these requirements. The main goal of the design is to help people confined to
wheelchairs access mammogram examinations and MRI testing. The fully motorized lift
operates with a 10 degree tilt and vertical translation of three to nine inches. The lifting
feature is operated by two motors connected to chains. Each motors is attached to two
sprockets, which will turn up and down threaded rods. The tilting feature is also going to
be run on chains and sprockets, similar to the idea of the lifting feature, except there will
only be one motor moving. The lift also has a ramp that allows for the patient to
effortlessly access the platform. The lift is controlled by a basic user interface, which
will allow for the patient or the healthcare practitioner to wirelessly control the lifting and
tilting portions of the device. The overall cost of fabricating this project is around $1500.
The Motorized Wheelchair Lift with Tilting Platform is a universal device which is
adaptable to most wheelchair sizes and weights, and will allow wheelchair confined
persons to access healthcare examinations in a timely and safe manner.
Wheelchairs are designed for the elderly, paraplegics, people with disabilities,
amputees and others that need to be transported due to health related issues. The reason
for fabricating this device is that many health care procedures are not accessible to
persons with disabilities. A wheelchair ramp calls for a specific slope, which is ADA
compliant, and a health care facility that does not have one may not have the room or
4
financial means to build one. For example, portable diagnostic units may not have the
proper lift device to place the patient in the machine or may not have an accessible
entrance to where the entity is stationed. A portable lift device is a much more sensible
solution. Overall, this device is beneficial in any location that is not accessible to persons
with disabilities.
People with disabilities comprise the largest minority group, which consist of 15
percent of the US population. People with disabilities may result from disease, injury, or
age and may lead to everyday use of a wheelchair to accommodate their lifestyle.
Cerebral palsy, muscular dystrophy, multiple sclerosis, spinal injuries, cancer, mentally
handicapped, and the elderly are all types of diseases or injuries that the population faces
leading to possible wheelchair use. These individuals that encounter these types of
disabilities could all benefit from The Motorized Wheelchair Lift with Tilting Platform in
receiving appropriate healthcare and screening without facing the normal obstacles due to
height and movement. Depending on the progression of many diseases or the severity of
certain injuries, the individual may or may not need another person to aid in operation.
People with disabilities contend with physical and situational barriers that complicate
everyday living including trips to the doctors. The healthcare field is in most cases
unable to provide adequate healthcare to the disabled due to improper treatment and
screening because the disabled does not have the means to access certain equipment for
appropriate examinations.
During a patient’s stay in rehabilitation they will most likely be undergoing many
clinical tests. The person with disabilities is constantly being placed on tables, chairs,
and in CT and MRI machines. This is why it is important for the Motorized Wheelchair
Lift with Tilting Platform to assist in undergoing clinical tests. The lift makes the job
easier for the healthcare practitioner and it more comfortable for the person confined to
the wheelchair because the patient is painlessly raised and tilt to reach the desired height
and angle. This is especially convenient for persons with disabilities who are obese
because it may be harder for them to properly position themselves for medical
procedures.
People become paralyzed for multiple reasons, such as a spinal cord injury, a birth
defect, or a stroke. If these people require the use of a wheelchair they will need a means
of accessing healthcare procedures safely and effectively. Therefore, it is important to
accommodate persons with disabilities with the Motorized Wheelchair Lift with Tilting
Platform.
For this device safety is a major requirement. The base must be stable enough to
avert tipping if the maximum load is concentrated at any position other than the center.
The motorized controls must be accessible and easily manipulated by the user no matter
what his/her disability. The speed that the motor raises and tilts the platform must be
within appropriate limits as to not injure the user. A manual function should be
integrated in the incident of an electrical failure while the platform is in a raised position.
5
A constraint of the platform is that there are many styles and sizes of wheelchairs,
so the device must be compatible with many different designs. The device must be
congruent with as many types of wheelchairs as possible for it to be useful, which means
it must be adaptable to multiple wheel sizes and motorized and non-motorized
wheelchairs. The device is also constrained by the maximum amount of weight it can lift
and tilt.
Market Research
There are some wheelchair lifts that exist on the market for consumers, but
nothing that is specific to the Motorized Wheelchair Lift with Tilting Platform’s concept.
Such items include a seat that tilts to help the individual standup out of the chair, if they
have a hard time raising up or lowering themselves down into the chair. There is also
another rather large, in size, device that acts as an elevator for a wheelchair. This device
can raise a person to a much greater height than Motorized Wheelchair Lift with Tilting
Platform will, but it is extremely large for the situation that the Motorized Wheelchair
Lift with Tilting Platform will accommodate for, and this device also does not tilt 10
degrees for an increase in the advantages for use. This type of lift is extremely expensive
at a price near $8000 from “Adaptive Engineering LTD.”
The market also offers a wheelchair lift that permanently attaches to a vehicle,
which has a high popularity in handicapped transportation vehicles. This device is not
transportable since it stays attached to the vehicle, the Motorized Wheelchair Lift with
Tilting Platform however will be able to be transported for a variety of uses including
storage purposes. The Chair will be vital when treating patients in doctor’s offices and
in clinics, where space maybe an issue. Having the device transportable allows the
healthcare provider appropriate and efficient storage when not in use, or permits the
wheelchair bound individual to bring the device with them to appointments.
There are many devices wherein the wheelchair tilts. This is a problem because
the patient will need to purchase a chair which tilts unless they have the Motorized
Wheelchair Lift with Tilting Platform at their doctor’s office. If the patient does not have
enough money to purchase the tilting wheelchair, it will be extremely complicated for the
doctor treating them to perform certain necessary medical procedures.
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Methods:
Design One
Static and Material Analysis
The platform will be lifted by a scissor jack mechanism. This is a commonly used
mechanism for many similar lifts however none of those lifts have been adapted for our
purposes. The mechanism works by manipulating two side by side scissors which are
linked by a cross bar. The actuator will push on the cross bar. One of the legs of each of
the scissor will be free to slide across the length of the base and across the length of the
platform. As it does this, the angle between the legs of the scissor expand and contract
based on the expansion and contraction of the actuator. As the angle decreases the legs
get closer together, thus pushing up on the platform and vice versa.
Analysis of the forces on the jack:
Force on Platform
θ
Gravitational Force
Force of Actuator
Normal Force
7
Scissor Jack Analysis
First we must determine the force necessary to move the lift when it is in its minimal
height of 3 inches. The legs are approximately 29 inches long.
Analysis of the translation of force from actuator to vertical lift
Θ = angle between horizontal and scissor leg
Arctan(3 in / 29 in) = θ => 5.96 degrees
The motor must provide the following power to begin to push the scissor jack
P = power = load / θ
P= 500 lbs / tan (5.96) = 4800 lbs
Platform
The platform will be made from 1018-FL Carbon steel. It is a disc sits upon ball bearings.
These ball bearings will hold 100 lbs each. Since there will be many ball bearings, the
weight will be evenly distributed amongst the bearings. Concordantly, the ball bearings
will be able to handle the load easily.
(Yield Strength = 53700 psi)
Load = Weight of turntable, platform, patient and wheel chair = 500 lbs
This load is idealized as one load in the center of the platform.
Ay =Vertical reaction along A
By = Vertical reaction along B
Cy = Vertical reaction along C
Dy = Vertical reaction along D
C
A
W
B
D
Due to symmetry:
A=B=C=D
∑Fy = 0
0 = A + B + C + D – 500lbs
8
500lbs = A + B +C + D
Therefore:
500 lbs = 4*A, each end of the jack cross bar must support 125 lbs, well within material
limits.
a
b
∑Ma = 0, counterclockwise is positive
-500lbs*(44 inches) + MB = 0
MB = 22000 lb*in
∑Mb = 0, counterclockwise is positive
500lbs*(44 inches) - MA = 0
MB = 22000 lb*in
The moments on each end are equal.
Scissor Jack Analysis
Analysis of the translation of force from actuator to vertical lift
Starting torque calculations. Assume the scissor length will be 29 inches and the minimal
height will be 3 inches.
Rotational Component
The platform will sit on ball bearings and be driven by a rubber belt system for
safety reasons. It is also much easier to replace a belt than a chain. Also should a person
get caught in the belt, the coefficient of friction is low enough to allow the platform to
slip, thus preventing the patient from being dragged in to the mechanism.
Fmax = Force necessary to turn the platform given the coefficient of friction between
rubber and metal.
Fmax = (μs)* (N)
μs = .55 for rubber against metal
9
Fmax = .55 * (500 lbs)
= 275 lb*ft needed to tilt platform
Electrical Analysis
Our design involves an integration of several mechanical components to provide
appropriate motion. For these parts to operate there must be an electrical circuit, which
connects them to a power supply. This basic design consists of a 12V battery connected
to a motor and a linear actuator. The motor will provide rotational motion and the
actuator will provide the linear translation. Both the linear actuator and motor will be
controlled by a microcontroller and an H-bridge circuit will drive the motor. There will
be a voltage regulator to control the voltage running to the microcontroller. The control
panel will consist of two toggle switches that dictate the direction of the given motor.
Both are to be set at a specific speed and set in motion by the movement of the
appropriate toggle switch.
A microcontroller is a highly integrated chip that contains all the components
comprising a controller. Typically this includes a CPU, RAM, some form of ROM, I/O
ports, and timers. Unlike a general-purpose computer, which also includes all of the
components, a microcontroller is designed for a very specific task – to control a particular
system. Our microcontroller will accept inputs from the user interface and thus provide
outputs to drive the H-bridge circuit motor control and linear actuator.
A voltage regulator is a small device, or circuit, that regulates the voltage that is
fed to the microprocessor. Since the required voltage of most microprocessors is less
than 3.5 volts, the job of the voltage regulator is to reduce the signal running through the
circuit to the microprocessor. Typically, voltage regulators are surrounded by heat sinks
because they generate significant heat. Some voltage regulators, particularly those
packaged as a voltage regulator module (VRM), are voltage ID (VID) programmable,
which means that the microprocessor can program the voltage regulator to provide the
correct voltage during power-up.
An H-bridge is a specially designed circuit to drive a DC motor. The H-bridge
circuit is easy to operate and requires 6 to 40 volts DC of motor power. There are two
logic lever compatible inputs, A and B, and two outputs, A and B. If the A input comes
in high, the output A goes high and the output B goes out low. This causes the motor to
operate in one direction. If B is the driven input the opposite occurs and the motor
operates in the opposite direction. If both of the inputs are low, the circuit consumes no
power; the motor is not driven and can freely “coast.” In most H-bridges, when both
inputs are high, the circuit self-destructs. However, it can be designed so that when both
inputs are driven, the motor is shorted as braking occurs.
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Figure 1: Example of an H Bridge
http://www.bobblick.com/techref/projects/hbridge/hbridge.html
Figure 2: An Example Truth Table for an H-bridge
input | output
A | B | A | B
--------------0
0 | float
1
0 | 1
0
0
1 | 0
1
1
1 | 1
1
The integration of these electrical components is exemplified in the following flowchart,
figure 3. Figure 4 demonstrates the power supply hook up for our design.
Figure 3: Electrical Components Connections
User Interface
Microcontroller
Linear Actuator
H-bridge
Rotational Motor
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Figure 7: Power Supply Connections
Motor Control
Circuit
AC Supply
Linear Actuator
12V Battery
5V Regulator
Remote Control
Circuit
Rotational Motor
12
Design Two
Static and Material Analysis
Design II has a completely different lifting mechanism. This design utilizes a
pneumatic bladder. The bladder is designed like an accordion. Metallic rings surround the
bladder. When the bladder expands, the rings constrict the balloon expansion. Thus, the
bladder expands uniformly along the vertical axis. This prevents random horizontal
forces from the normal forces along the spherical surface of the bladder. The bladder also
has the added advantage of having a slim profile when contracted. An air compressor
powers the pneumatic actuator.
To stabilize the platform against the horizontal forces that may arise from the
actuator expansion, the platform will have four metal posts running through it at each
end. This “four post bed” design will provide excellent stability for the platform.
Platform
Load = Weight of platform, person and wheel chair idealized as a point force
Ey =Vertical reaction along E which is the center of the actuator
∑Fy = 0
0 = E – 500 lbs
500 lbs = E
Load
E
Since the only vertical force exerted against the platform comes from the single actuator,
the actuator capacity must be at least 500 lbs.
“Four Post” Analysis
To stabilize the platform against the horizontal forces that may arise from the
actuator expansion, the platform will have four metal posts running through it at each
end. This “four post bed” design will provide excellent stability for the platform because
it locks the platform in to place, restricting any horizontal movement. The posts,
individually, will be thick enough to withstand 500 lbs of force exerted on it with out any
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yielding. Adding the strength of four-post system will concurrently increase the amount
of horizontal force the posts can take allowing for a high factor of safety.
Analysis of the stress should the load shift to one post.
Assumes maximum load is placed on one of the posts.
Load
Τ = F/(π*d2) = 2000 N/ .0081 m2 = .246 MPa
This is well under the yield strength of the proposed alloy given the thickness of the bar.
Rotational Component
For the rotational component for the lift, we opted to use the same mechanism as
in Design I, this being a metallic disc, which rests on ball bearings. The turntable is
driven by a belt drive. This is used to prevent the hazard of having a gear system place
near the patient.
W = Fmax = (μs)* (N)
μs = coefficient of friction = .55 for rubber against metal
W = .55 * (500 lbs)
= 275 lbs needed to tilt platform
Electrical Analysis
For this design we will be using pneumatic actuator and a rotational motor. Based
on our mechanical design this flow chart represents the electronic requirements of our
system.
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Figure 1: Electrical Components
User Interface
Microprocessor
Pneumatic
Actuator
H-Bridge
Rotational Motor
Figure 2: Power Supply Connections
User Interface
Microprocessor
12V Battery
Pneumatic
Actuator
5V Regulator
Rotational Motor
The power supply will be a 12V battery. We will utilize the 5V voltage regulator
to control the voltage running into microprocessor. Limit switches will be used to make
sure the actuator doesn’t drive the platform into the ground. The user interface will
consist of two toggle switches to provide control over the motor and actuator. For
example, when the toggle switch is in an on position, the circuit is completed and thus the
motor is on. When the toggle switch is moved to the off position, the circuit is open and
15
no current will flow to the motor, thus stopping rotation. When the toggle switch is
moved to the opposite on position, the motor will operate in the opposite direction, as
indicated in figure 3.
Figure 3: User Interface
Off
Down
Up
Off
Clockwise
Counterclockwise
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Design Three
Static and Material Analysis
The lift for design 3 will be operated by a screw lift system. A motor is linked via
chain to four threaded gears. These gears are like nuts which are placed on bolts.
Similarly the gears are screwed on to 4 threaded rods at each corner of the platform. As
the motor turns the chain, the chain turns all 4 gears simultaneously. As the gears turn,
their rotation pushes the platform up and down as the gear travels up and down the rod.
The materials remain the same as design II save the gear material, which is unknown at
this point other than it will be steel.
Wheelchair Wheel Loads: 30” apart, 400 lbs
Cg of Platform
Platform 44”
A
B
Force of gears
Static Analysis
Assume that counterclockwise motion is positive
ΣMA = 0
-(7 inch)*(200 lbs) – (22 inch)*(30 lbs) –(37 inch)*(200lbs) + (44 inch)*(By) = 0
By = 215 lb * in
ΣMB = 0
(7 inch)*(200 lbs) + (22 inch)*(30 lbs) + (37 inch)*(200lbs) - (44 inch)*(Ay) = 0
Ay = 215 lb * in
The moments are equal and opposite.
ΣFy = 0
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Fg = force of gears
4Fg = 400 lbs + 30 lbs
Fg = 107.5 lbs for each gear
Bending Stress
Σm = (M*c) / I
I = (1/12)bh3 = (1/12) * (43”)*(.24”) = 86 in4
M = 215 lb in (from above)
C = 1/8 in
Σm = .3125 ksi. Minimal deflection will occur
Screw Drive Analysis
The threads used will be Acme threads. This type of thread is the standard used
for all load bearing and or industrial applications. Our design call for an Acme threaded
rod of 1 inch diameter with 8 threads per inch. We used a coarse thread to ensure that the
threads have sufficient strength to hold the platform in place.
Torque Calculations

Fd l  d (sec  )
*
2 d  l (sec  )
F = axial force placed on the threads
d = pitch diameter
μ = coefficient of friction
α = thread angle
l = pitch
For our purposes:
F = 500 lbs, we will assume the worst case, in that 1 gear will hold all 500 lbs
d = .0625 inches
μ = .8, this is the coefficient for steel on steel, the device will be lubricated, but for
analysis purposes we will assume a worst case scenario
l = .0625
α = 29° for Acme threads
τ = 55.286 lb*in
18
Our lifting motor is rated at 500 lb*in which is more than sufficient for our purposes.
Therefore, we will not use any gear ratios for mechanical advantage.
One rotation will move the gear up one thread. Since the gear ratio is 1, input rotation
speed is the same as output. Our motor is set at 6 RPM.
1 rotation = 1 thread
(6 rot / min) * (1 inch / 8 threads) * (1 thread / rot) = .75 inches / min
Turntable Analysis
The turntable is a steel disc, which will sit upon 12 ball bearings. Each ball
bearing has a 100 lb capacity so the 12 ball bearings can easily handle a 500 lb load. The
turntable will have a rod protruding from the center pointing to the ground. Attached to
that rod will be a gear. The rotational motor will turn this gear via chain and thus allow
the turntable to tilt.
W=μ*N
W = Torque
μ = coefficient of friction of flange mounted ball bearing
N = normal load
μ = 3*10-3 for ball bearings
N = 500 lbs, assume worst case
W = 1.5 lbs
ni = input rpm
Ni = number of teeth on input sprocket
no = output rpm
No = number of teeth on output sprocket
(ni/no) = (No/Ni) => no = ni * ((Ni/No) = 12 rpm * (11/60) = 2.2 rpm for the turntable
Rotational Torque Calculations
μ = 3*10-3 for ball bearings
N = 500 lbs, assume worst case
Rlarge = radius of large gear attached to turntable = 1.65 inches
Rsmall = radius of smaller gear attached to motor = .75 inches
Gear Ratio from Large sprocket to small sprocket = 2:1
Torque on turntable sprocket = (500 lb) (0.003) (1.65 in.) = 2.475 lbin.
Torque on motor sprocket = (2.475 lbin.) (1/2) = 1.2375 lbin.
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Initial torque is smaller than the 250 lb*in max torque of the proposed motor. While this
may seem like overkill, this ensures a maximal amount of safety and mechanical
reliability.
Electrical Analysis
The motorized wheelchair lift with Tilting platform consists of two motors driven
by two separate H-bridges. These will be controlled by a user interface with a joystick
and wireless remote control. This will transmit an RC signal, which will be received by
the microcontroller chip, which will in turn operate the appropriate H-bridge and
corresponding motor. The power supply will be one 12-volt DC deep-cycle battery, with
an alternate AC supply connection to recharge the battery.
The H-bridge circuits are both model MC7 from Diverse Electronic Services
(http://divelec.tripod.com/). The microcontroller is the RCIC2_SC (Radio Control
Interface Chip), also from Diverse Electronic Services. The MC7 is a motor controller
with a wide operating voltage, from 12 to 36 volts and a 35-amp capability that can be
controlled manually or directly from the microprocessor. The MC7 is a compact circuit
board approximately 3.75”x5.75” with four mounting holes, as demonstrated in Figure 1.
Figure 1: The MC7 H-bridge Motor Control
20
The RCIC2 is a preprogrammed PIC, which will accept a standard 1 to 2 ms RC
pulse from each of 2 channels and send the proper control signals to each of the 2 MC7s.
This allows for complete control of both direction and continuously variable speed of
each controller. Without any programming, we can control the direction of the motors
with a single controller found on a standard RC transmitter. The RCIC2 can be special
ordered with no mixing for our design so that a dual axis joystick may be used to control
both motors. Pushing forward on the vertical axis makes motor #1 go in one direction,
while speed is controlled by how far you push the joystick forward. Pulling back on the
joystick makes motor #1 go in the opposite direction, and the speed is controlled by how
far the joystick is pulled back. There is no control over motor 2 unless you move the
joystick off the center axis (+/- a small dead band). Moving the stick left or right on the
horizontal axis while keeping centered on the vertical axis will cause the second motor to
respond in a similar fashion as motor #1 did in the vertical. The following is a schematic
of the RCIC2 as found on the Diverse Electronics Website, as well as a sample printout
of the RCIC_SC RC control table:
Figure 2: A Schematic of the RCIC2
21
Figure 3: RCIC_SC RC Control Pinout Table
Pin Number
Pin Name
1
MCLR
2
Purpose
Connection
10K resistor connected to this pin
Other side of 10K resistor connected to +5V.
RA0
Not used
No Connection
3
RA1
Not used
No Connection
4
RA2
Not used
No Connection
5
RA3
Not used
No Connection
6
RA4
Not used
No Connection
7
RA5
Not used
No Connection
8
VSS
Ground lead
Connected to ground
9
OSC1
Connection for external frequency element
Connect to 10 MHz ceramic resonator
10
OSC2
Connection for external frequency element
Connect to 10 MHz ceramic resonator
11
RC0
Accepts CH1 pulse widths from 1 to 2 ms
From RC receiver CH1
(Forward-Reverse)
12
RC1
Accepts CH2 pulse widths from 1 to 2 ms
From RC receiver CH2
(Left-Right)
13
RC2
Outputs a logic 1 (+5V) when the CH1 input
pulse is more than 1.5 ms
Connect to the FWD tab on the MC7 board #1
14
RC3
Outputs a logic level 1 (+5V) when the CH1
input pulse is less than 1.5 ms.
Connected to the REV tab on the MC7 board #1
15
RC4
Outputs a logic 0 (Gnd) when the CH1 input
pulse is 1.5 ms +/- dead band
Connected to an LED & resistor which lights to show
when received pulse is 1.5 ms
16
RC5
Outputs a logic 0 (Gnd) when receiving RC
pulses
Connected to an LED & resistor which lights to show
when receiving pulses
17
RC6
Outputs a logic 0 (Gnd) when the CH2 input
pulse is 1.5 ms +/- dead band
Connected to an LED & resistor which lights to show
when received pulse is 1.5 ms
18
RC7
Serial out port, used for testing only
Not Used
19
VSS
Ground lead
Connected to ground
20
VDD
+5V
Connect to SW COM on the MC7 board #1 for a 5V
source.
21
RB0
Not used
No Connection
22
RB1
No signal/calibration Indicator
Flashes ~1X/sec when no sig., flashes rapidly while
calibrating, off otherwise
23
RB2
Outputs a logic 1 (+5V) when the CH2 input
pulse is more than 1.5 ms
Connect to the FWD tab on the MC7 board #2
24
RB3
Outputs a logic 1 (+5V) when the CH2 input
pulse is less than 1.5 ms.
Connected to the REV tab on the MC7 board #2
25
RB4
PWM output port for the MC7 board #2
Connected to the PW tab of the MC7 board #2
26
RB5
PWM output port for the MC7 board #1
Connected to the PW tab of the MC7 board #1
27
RB6
Not used
No Connection
28
RB7
Not used
No Connection
22
Connection of the MC7s to the RCIC is simple as demonstrated in Figure 3. The
RCIC2 is mounted on the first MC7 with connections running to the second MC7. At
this point, all that is needed is an RC receiver, batteries, limit switches and two motors.
Figure 4: An Illustration of Connections of the MC7s to the RCIC2
The following is a connection diagram of the RCIC2.
Figure 5: RCIC connections:
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Connection to the receiver will also be relatively simple, as the RCIC comes
complete with 4 universal leads (one red for the +5V connection, one black for the
negative connection, 1 white for the channel 1 output and 1 yellow for the channel 2
output). These leads will enable us to connect to the receiver regardless of what brand
we purchase.
The final component to the electrical design is the addition of limit switches.
These will control how far the motors run so as to keep the motor from driving the
platform off the threaded rods, or even worse, into the ground.
The following is a final overview of our electrical system for the optimal design.
Figure 6 is a flowchart of the connections of the basic electrical components. Figure 7
demonstrates the flow of power through the system.
Figure 6: Electrical Components Connections
User Interface
Standard RC
Transmitter
Standard
RC
Reciever
RCIC2
Microcontroller
Limit
Switch
Limit
Switch
MC7 #1
H-Bridge
MC7 #2
H-Bridge
Rotational
Motor
Translational
Motor
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Figure 7: Power Supply Connections
Motor Control
Circuit
AC Supply
Translational
Motor
12V Battery
5V Regulator
Remote Control
Circuit
Rotational
Motor
Power Requirements:
There are two motors in this design, one for rotational motion and one for translational
motion. The full load ampage for both motors is 6.5 amps. The battery can supply 28
amps for 20 hours and thus has a capacity of 560 amp hours. Since the current divided
by the full load amps determines the battery life, our battery can last 86 hours without
being recharged. Based on the translational velocity calculated in the mechanical
analysis, we can use dimensional analysis to calculate the number of cycles that can be
run per battery life.
86 hrs (60min/1hr)(.75 in/min)(1 cycle/6 in) = 645 cycles
The rotational motor also has a full load amp of 6.5 and a full load torque of 250 lbin. It
is also a 12 VDC motor with a 1/15 HP and 12 RPMs. The same battery supplies power
to both. The rotational motor can run for 86 hours when used solely for rotation and run
continuously until the battery dies. When both of the motors are run together, the battery
can last for 31 hours. Since this is more than a day, run continuously, this is plenty long
enough for our specifications.
25
DESCRIPTION
Bottom View of Platform
54.00
1.34
1.34
7.00
21.43
Turntable
Platform
44.00
10.00
3.00
3.00
26
DESCRIPTION
Top View of Platform
54.00
Platform
Turntable
44.00
Motor Box
7.00
10.00
Railing
27
DESCRIPTION
Side View of Platform Lengthwise
Railing
2.00
7.00
5.00
37.50
2.00
54.00
28
DESCRIPTION
Side View of Platform Widthwise
Railing
2.00
2.00
22.00
20.00
24.00
5.00
Motor Box
Platform
2.00
12.50
10.00
2.00
12.50
2.00
43.00
29
DESCRIPTION
Top View of Base
54.00
3.00
48.00
3.00
3.00
19.00
Base
44.00
19.00
3.00
30
DESCRIPTION
Side View of Base Lengthwise
50.00
2.00
42.40
20.00
20.50
2.20
Base
0.50
31
DESCRIPTION
Side View of Base Widthwise
1.60
1.60
20.00
20.00 20.50
Base
2.20
13.20
10.00
13.20
0.50
2.20
44.00
32
DESCRIPTION
Side View of Whole Device Widthwise
Railing
2.00
2.00
2.00
2.00
22.00
13.00
10.00
13.00
33.50
5.00
Motor Box
Platform
2.00
1.60
1.60
9.00
0.50
Base
3.20
12.20
10.00
12.20
3.20
44.00
33
DESCRIPTION
Side View of Whole Device Lengthwise
R 2.00
Railing
2.00
2.00
46.00
2.00
22.00
7.00
33.50
5.00
46.40
Platform
1.60
2.00
9.00
2.20
Base
0.50
54.00
34
DESCRIPTION
Top View of Platform without Railings
54.00
12.50
11.50
11.50
12.50
10.00
7.00
Turntable
Platform
9.00
44.00
9.00
10.00
10.00
35
Discussion of the Optimal Design:
We decided to use the MC7s but were unable to use the RCIC2 wireless
transmitter. Instead we opted to use a Linx KH wireless transmitter – receiver system.
This system has 8 inputs/outputs which is more than what we need. To interface with the
transmitter, we used simple ON-OFF-ON toggle switches.
On the transmitter I used S2, S4, S5, and S7, which transmitted to their respective D ports
on the receiver. The D ports on the receiver then output 5 volts to Ports B 0 and 1, 6 and
7. To limit the amount of noise on the receiver I recommend isolating the power supply
as much as possible. This will increase the reliability of the receiver signal to the
microprocessor.
We used Zippy brand limit switches to govern the tilt and upper and lower limits.
They were place strategically at the limits so that they would stop the microprocessor
(PIC16F874) when necessary. The microprocessor governed the entire system and sent
out the signal to the MC7s. A PCB board was created to house the entire system. This
PCB board has all the pads for the appropriate inputs and outputs and has ports for
powering +5V systems when used in conjunction with a TI7805 regulator.
36
PCB Board Schematic
Wiring Diagram
Electronics Flow Chart
Transmitter
Receiver
Limit
Switches
Microprocessor
MC7
MC7
Motor
Motor
37
Diagrams
38
39
Conclusion:
The optimal design is going to be a modification of Design Number Three in
order for our project to tilt. This is a very sound idea seeing as there is a lift in the
machine shop that has the same basic principles of running on gears and chains, but with
no motor. The lift is going to be made to do exactly what it is supposed to, have a
vertical lift of three to nine inches and have a tilting angle of 10 degrees. This lift will
run on motors, sprockets and chains to accomplish the aforementioned. Safety features
as of right now, include limit switches and possibly a safety skirt to go around the
threaded rods when in the raised position. All of the standards from ADA and ASME
have been looked at, and the lift will be fully compliant with them. As of right now, the
parts list is under budget seeing as the metal will be purchased from the machine shop.
This device will be used to help people who are confined to wheelchairs.
40
Appendix A: Technical Specifications:
Dimensions
Height:
Platform Length:
Platform Width:
Ramp Width:
Vertical Translation:
Maximum Tilt:
Tilt Speed:
Translation Speed:
24in
54in
44in
14in
2.5”–9”
10 degrees
6 RPM
1 in/min
Electrical Parameters
Internal Power:
1 Battery Life:
12 VDC
~111hrs with each motor consuming half the battery
Mechanical Requirements
Maximum Weight Capacity
(including wheelchair):
300 lbs
Materials
Platform:
Base:
Rod Holders:
Plate Sandwich:
12-gauge structural steel
12-gauge structural steel
3” Aluminum stock
3” Aluminum stock
Lift Motor Requirements
Type:
Gear Ratio:
Torque:
Current Draw:
12 VDC Parallel Shaft Gearmotor
267:1
500 in-lbs
6.5A
Tilting Motor Requirements
Type:
Gear Ratio:
Torque:
Current Draw:
12 VDC Parallel Shaft Gearmotor
133:1
500 in-lbs
6.5A
41
Appendix B: Timeline:
42
Appendix C: Budget:
43
Appendix D: Engineering Standards:
The engineering standards for this project are defined in the ADA Standards for
Accessible Design. This has been outlined by the United States Department of Justice.
This booklet is for the rites of people confined to wheelchairs and all of the design
standards that go along with it.
The ADA requires that the least possible slope be used for any ramp. The
maximum slope will be 1:12 (Section 4.8.2). Section 4.13.7 Two Doors in Series states
that the minimum maneuvering clearance at two doors in series is 48 inches. Therefore
the width of the device and diameter of the Tilting platform fulfill this requirement
because they are only 48 and 38 inches, respectively. This will allow the lift to enter any
room in the hospital, which is its intended purpose. Section 4.2.4.3 talks about clear floor
or ground spaces for wheelchairs. Ground and floor surfaces shall be stable, firm and
slip-resistant. The lift complies with the code because on the ramp there will be slipresistant materials, and from the analysis of the materials, we know that everything will
be sturdy enough the hold the given weight. Section 4.8.7 is about edge protection,
meaning that ramps and landings with drop-offs should have curbs, walls, railings or
projecting surfaces which will prevent people from slipping off the ramp. The lift will be
equipped with railings on three of the four sides, and the ramp does not have a significant
slope therefore it is unnecessary to have anything on the side of the ramp. Section 4.27.4
requires that controls and operating mechanisms shall be operable with one hand and
shall not require tight grasping, twisting of the arm or pinching. The force to activate the
controls can be no greater than 5 lbf. The projected control for use right now is the size
of an automatic car starter. Therefore, there will be no problems with the ADA
standards.
The Motorized Wheelchair Lift with Tilting Platform is environmentally safe. It
is designed to be used indoors, i.e. in a hospital and is going to run on a battery. Since it
will run on a battery, there will be no harmful toxins emitted into the air.
This device is a class one device; it presents minimal potential for harm to the
user. The only harm that this device can cause to the user is if it the directions are not
read, resulting in the lift being used improperly. Also, this device will not be used in
vivo, so it will not take very long for the device to be approved.
The parts being ordered for this project are from well-known companies like
Grainger and McMaster. All materials are ready to ship almost immediately because they
are common. By ordering items from the same companies, the compatibility issue is
reduced. Also, these companies have warrantees and some of them will even come out to
fix a broken part.
44
Acknowledgements:
The team would like to thank Serge and Rich in the machine shop for all of their
help looking for parts and for advice. We would also like to thank Chris Liebler and
Francisco Rodriguez-Campos for their help and support building our EKGs. Finally, we
would like to thank Dr. Enderle for his guidance during this difficult process.
45
References:
www.mcmaster.com
www.grainger.com
www.usdoj.gov/crt/ada/stdspdf.htm
Diverse Electronics Website
http://www.bobblick.com/techref/projects/hbridge/hbridge.html
46