SALUKI ENGINEERING COMPANY
Literature Review
Team 76 - MOWR
Team Members
Project Manager: Rachel Parth
Dylan Hartman
Brittany Murphy
Nathaniel Sparks
Zachary Tennessen
Christopher Tyra
10/6/2011
The objective of this project is to create a fully autonomous lawnmower. Upon
completion, it will be able to mow a 10 by 15 meter yard, and avoid stationary and moving
obstacles.
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Table of Contents
Table of Figures ............................................................................................................................................ 3
Tables ............................................................................................................................................................ 4
T94-GPS Lawnmower-Design...................................................................................................................... 6
Case Western Reserve University CWRU Cutter C design review .............................................................. 6
Batteries ........................................................................................................................................................ 8
Robotics ........................................................................................................................................................ 9
Platform: ....................................................................................................................................................... 9
Actuator: ..................................................................................................................................................... 10
Microcontroller: .......................................................................................................................................... 11
Motor controller: ........................................................................................................................................ 11
Sensors: ....................................................................................................................................................... 12
GPS ............................................................................................................................................................. 14
Lawnmower ................................................................................................................................................ 16
Motors ......................................................................................................................................................... 17
Wheels ........................................................................................................................................................ 18
Works Cited ................................................................................................................................................ 20
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Table of Figures
Figure 1 ......................................................................................................................................................... 5
Figure 2: CWRU Cutter 2 Isometric View ...................................................................................................... 7
Figure 3: Tracked Robot
Figure 4: Wheeled Robot................................................................. 10
Figure 5: Cytron Gear Motor with Encoder ................................................................................................ 10
Figure 6: Parallax BASIC Stamp 2p 40-pin Microcontroller......................................................................... 11
Figure 7: Vex Bumper Switch ...................................................................................................................... 13
Figure 8: Cytron Incremental Rotary Encoder ............................................................................................ 13
Figure 9: Ultrasonic Range Finder ............................................................................................................... 13
Figure 10: RXM-SG GPS module with External Antenna............................................................................. 14
Figure 11: GPS Receiver Module ................................................................................................................. 15
Figure 12: PBM 648 SiRF Internal Antenna ................................................................................................. 15
Figure 13: Yardworks 18” 12A electric lawnmower.................................................................................... 17
Figure 14: Marathon Electric Brake Motor ................................................................................................. 18
Figure 15: Acquired Spindle Wheel............................................................................................................. 18
Figure 16: Motorized Wheels...................................................................................................................... 19
Figure 17: Battery hookup (top) Control Box hookup (bottom) ................................................................. 19
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Tables
Table 1......................................................................................................................................................... 10
Table 2......................................................................................................................................................... 11
Table 3......................................................................................................................................................... 11
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Previous Design Review
Figure 1
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T94-GPS Lawnmower-Design
The previous time that SIUC had a senior design project based around the Autonomous
Lawnmower Completion was during the Fall 2009 semester. The report from this attempt
compiles some of the basic functions the previous design had but is incomplete due to issues that
arose. The previous team decided on using the rear drive wheels from a wheel chair which are
independently driven by separate motors. This decision was made after looking at using a riding
lawnmower as the base drive and mowing system with a computer incorporated into the controls.
This was decided to be too costly, outside of their expertise, and would take too much time to
engineer a working model. A wheelchair was donated to the team and the parts used from the
wheelchair were the rear wheels and motors, the front spindle wheels, and the controller for the
rear drive motors. Since it was chosen not to use a riding lawnmower the team decided that an
aluminum square tube frame would be the body of the lawnmower.
The basic frame model was shown in the report and comments were made to the top
heaviness of the design which limited how steep of an incline the mower could transverse. The
frame was supposed to hold the two 12 volt batteries on the middle platform which caused a
great deal of the top heaviness. These batteries were hooked up in series to provide the 24 volts
required to run the motors. These batteries were also donated to the team but were found unable
to sustain a charge for very long and would have needed to be replaced with more efficient
batteries if real world commercial application was considered. The upper platform of the frame
was to hold the personal computer that was to control the lawnmower. Little to no details were
provided about this portion and is considered to be one of the reasons the design was
uncompleted. Another missing component was any type of mower deck to cut grass. The design
team ran into budgeting issues and decided they couldn't afford to purchase an electric push
lawnmower for the project. The team decided that an electric lawnmower would be the best
choice for the mower portion since it allowed it to be controlled by a computer and didn't require
additional fuel sources besides the batteries. The two batteries required to run the wheel motors
were the only ones mentions and it can be considered that additional batteries may have been
needed to supply operational power to the mower deck. Sensors suggested for the design were
GPS and laser but again due to budgeting and team issues these were neither implemented nor
discussed in depth.
Case Western Reserve University CWRU Cutter C design review
Case Western Reserve University was the 1st place winners of the 2010 ION Robotic
Lawn Mower Completion. Their design also distinguished itself as the only mower to cut over
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50% of the required field for the full cash prize. Their project had been worked on and
repeatedly submitted to the competitions since 2008. This allowed for extensive research to be
done on the controlling program and the sensors used. This also ended up with a substantially
larger budget than the SIUC team. The CWRU Cutter C design was in it's 2 edition. Their
design used a set of swivel wheels for the front and a pair of independently driven wheelchair
wheels for steering and propulsion. These were connected to a custom made metal frame that
had an electric cordless push mower deck attached to the bottom along with a wire edge trimmer
attached to a separate 12v electric motor. On top of the frame sits a water proof Pelican case
housing the control computer and to which the differential GPS and cameras were attached.
Below the computer case and directly above the mower deck situated to the front of the frame
are the two marine grade 12volt batteries connected in series for 24v and running at 38 Amp
hours.
Figure 2: CWRU Cutter 2 Isometric View
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Batteries
In order to run our autonomous lawn mower, we had to figure out a way to make a
corded push mower that runs off of AC run off of batteries which supply a DC. For this, we must
first calculate out how much power we need in order to run our push mower. The mower is 120v
and uses 12Amps, to calculate out how much power we need to run it for one hour, we can use
the following equations.
𝑃𝑜𝑤𝑒𝑟(𝑊𝑎𝑡𝑡 𝐻𝑜𝑢𝑟𝑠) = 𝑉𝑜𝑙𝑡𝑠 ∗ 𝐶𝑢𝑟𝑟𝑒𝑛𝑡(𝐴𝑚𝑝 𝐻𝑜𝑢𝑟𝑠) → 𝑃𝑜𝑤𝑒𝑟 = 120𝑉 ∗ 12Ah
𝐴𝑚𝑝 𝐻𝑜𝑢𝑟𝑠 = 𝐴𝑚𝑝𝑠 ∗ 𝐻𝑜𝑢𝑟𝑠 𝑟𝑎𝑛
Using this we calculate out that we need 1440 watts of power to run the mower for 1 hour. This
tells us that we are going to need some serious power and that we may need more than one. So
now we start looking into which type of battery is best suited for our need. There are two main
types of batteries functionality wise that we need to consider. There are Starting batteries and
then there are Deep cell batteries.
Starting batteries, sometimes called SLI for starting, lighting, ignition, are used more for
starting and running engines. They are commonly made with many thin lead plates that have a
more “sponge” like make up. This composition allows for the plates to have a greater surface
area compared to a solid plate. This allows a greater amount of current to flow from the plates,
which is what makes this the ideal battery type for engines that need a large amount of current at
one time to start, then just small amount to keep the cycle going.
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Deep cell or Deep cycle batteries are more commonly used in circumstances where small
or medium amounts of energy are needed for extended amounts of time. Deep cells are good for
marine uses on boats for trawling motors or stereos or with recreational vehicles with power
draining appliances. These types of batteries are made up of thicker lead plates that are solid, or
non-sponge like. This gives the plates less surface area and therefore less instant power. Though
they are intended to be used for longer drawn out power consumptions, these batteries can also
be used for starting engines. But due to the lack of instant current that the plates provide, it is
better to go a little larger than needed to allow for more current to be drawn upon.
For our project, we are not in need of large amounts of current at any one instant
because we are not starting any large engines. We will have a DC brushless motor for our mower
and a few other power consuming devices. Due to our energy needs, our best choice of battery
would be one or two Deep cell batteries that can provide us with the amount of energy we need
for the amount of time needed. Our project will need to be able to run off of the battery for no
less than 20 minutes. That is the maximum amount of time allotted to a team to mow the given
yard. So we need to find a Deep cell battery or batteries that will be able to give us the power
needed without weighing too much.
Robotics
In order to create an automated lawn motor, it is necessary to create a version of an artificial
intelligent lawn motor. This requires a version of a robot lawn motor to be built, and that in turn
involves many different components. Parts of a robot consist of:





Platform
Actuator
Microcontroller
Motor controller
Sensors
Team 76 will illustrate briefly what each part does in the overall system of a robot and offer
possible choices for each part including specifications and cost of each component.
Platform:
Platforms are the type of robots that will be built. They range from land (wheeled, legged or
tracked), to aerial to aquatic and finally to stationary robots.
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Figure 3: Tracked Robot
Figure 4: Wheeled Robot
Actuator:
An actuator is a device that will change energy to physical motion. For robots, it is to change
electrical energy into physical motion. Physical motion can contain of rotational or linear
motion. This will allow the robot to move in any direction on the ground. The actuator is also
known as a motor. There are several kinds of actuators; rotational actuators are AC, DC, geared
DC, R/C servo, industrial servo and stepper motors. Linear actuators are DC linear, solenoids,
muscle wire, pneumatic, and hydraulic.
Table 1
Name
Cytron 12V,
1140rpm,
6.37oz-in
Gear Motor
with Encoder
Tamiya
Worm Gear
Box
Gear Ratio
Voltage
Torque
Speed
Current
Price/unit
5:1
12 V
45mN.m
1140 rpm
0.9 A
$50.00
216:1,
336:1
3V
70 g-cm
9400 rpm
2.7 A
$13.97
Figure 5: Cytron Gear Motor with Encoder
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Microcontroller:
The microcontroller may be the most important part of the robot; it is in many cases considered
the ‘brain’ of the robots. The microcontroller is the device that will execute a program in order
to make the robot perform its task. This is also the device where outputs from various sensors
used by the robot will feed into, to complete different requirements as stated in the program.
Table 2
Name
Parallax BASIC Stamp
1 Microcontroller
Module
NanoCore12MAXC128
Module
Parallax BASIC Stamp
2p 40- Pin
Microcontroller Module
Processor Speed
# of I/O pins
Price/unit
4 MHz turbo
8
$29.00
8 MHz
40
$35.70
20 MHz turbo
32 and 2 dedicated
serial
$89.00
Figure 6: Parallax BASIC Stamp 2p 40-pin Microcontroller
Motor controller:
The motor controller assists in controlling the motor. The microcontroller has the program in its
memory, and is capable of directing the robot where to go and how fast to travel in that direction;
however it usually does not have enough power to power itself as well drive the motor. Thus the
microcontroller and the motor controller work in tandem – with the microcontroller reading its
program and the inputs from the sensor and directing the motor control to power the motor with
‘x’ amount of power. There are different types of motor controllers; some of these types are DC
motor control, servo motor control, stepper motor control, and linear actuator control.
Table 3
Name
Current
Operating
Voltage
Price/unit
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2A 5V-16V Dual
Serial Motor
Controller
Pololu DC Motor
Driver 3A, 5V28V- MC33926
2 A per motor,
total of 4 A
5V-16V
$19.95
3A
5V-28V
$23.95
Figure : Pololu DC Motor Driver
Sensors:
Sensors will allow the robot to explore and understand the environment it is in. There are many
different types of sensors out there, and they can be used alone or in combinations with others.
The outputs of these sensors will feed into the microcontroller, as before stated, to complete
various parameters that may be needed in the program. The different categories of sensors that
are being considered are:

Contact: An example of a contact sensor would be Vex Bumper Switch. This costs
$12.99/unit. It requires 5.06 ounces to trigger.
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Figure 7: Vex Bumper Switch

Distance: An example of this would be an encoder such as the Cytron Incremental Rotary
Encoder. This costs $135.48/unit, requires an input of 5 V – 24 V and consumes
approximately 120mA. This sensor also fulfills the requirement for postioning.
Figure 8: Cytron Incremental Rotary Encoder

Positioning: An example of this would be an ultrasonic sensor such as the Maxbotix LVMaxSonar-WR1 Weather Resistant Ultrasonic Range Finder. This costs $99.95/unit,
dectection ranges from 12” to 254” and has a 42KHz ultrasonic ping.
Figure 9: Ultrasonic Range Finder
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GPS
The GPS lawn mower has a lot of different types of GPS to choose from, but the main
choice of GPS chips are from the company Parallax. GPS stands for Global Positioning System.
The global positioning system use satellites orbiting Earth to receive a signal from the GPS chip
and use it to pinpoint your location. It records the time the signal was sent and received by the
satellite and sends information to other satellites to get their information. The more satellites
being used, the more accurate your location will be. A minimum of three satellites must be used
to calculate your two (2) dimensional location for most GPS. More satellites must be used to be
able to calculate your three (3) dimensional location.
GPS currently being looked at is the RXM-SG GPS module with external antenna. It is
made by Parallax and it has twenty (20) satellite orbiting Earth two (2) times a day. This GPS
chip can connect with a regular computer using a USB port or with a microcontroller. The chip
sends NMEAD0183 data to a program to show its location given from the satellites. It can use
the internet to show its location on Google Maps. The chip five volts (5V) to work properly and
is battery backed up. The accuracy is twenty yards (20yds) or sixty five feet (65ft). The cost is
$79.99.
Figure 10: RXM-SG GPS module with External Antenna
The next possible GPS Receiver Module. Also made by Parallax has twelve satellites.
The chip also sends NMEAD0183 data to a program to show its location given from the
satellites. To make it more accurate it uses WAAS which is Wide Area Augmentation. In order
to use the WAAS there needs to be a substation within range. It uses five volts (5V) to run the
chip and calculates the date, time, velocity, navigation, etc. A downfall of this particular chip is
that it must be outdoors in an unobstructed area and can be disrupted by a high level of magnetic
fields. The accuracy of the chip is within five meters (5m).
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Figure 11: GPS Receiver Module
The final chip that could work for the lawn mower is also made by parallax. The GPS
chip is PBM 648 SiRF Internal Antenna. The GPS chip has 20 satellites to receive data from. It
sends version two point two (2.2) of NMEAD0183 coordinates to the computer to navigate with.
It is accurate to within five meters (5m) and is also supported by the WAAS.
Figure 12: PBM 648 SiRF Internal Antenna
In order to properly integrate everything together and to get everything be automated
there will have to be a program to make it move, run the GPS chip, run the mower deck, etc.
Some possible programming languages that might be used are C, C++, Java, and Visual Basic.
The programming language C is developed by Microsoft. It is a relatively small
language in comparison to C++ and other languages. It is a high level assembly language that
does not have a good compiler. The language is easy to make errors in due to the size of the
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language. The programming language can be used on different operating systems but is
primarily used on Windows.
C++ is a more modern programmable language. C++ is also created by Microsoft. It
uses new features which makes it easier to program in and debug programs in. It is used by most
consumers to create more sophisticated programs. Overall is good to use for new programmers
and there is a wide variety of online tutorial. C++ is used on a wide variety of operating systems
but primarily on windows.
Visual Basic is made my Microsoft and is able to support a lot of other languages such as
C, C++, Python, Ruby and many others. It is good for creating Graphical User Interface (GUI).
It is available only in Microsoft Windows.
Java is created by Sun. It is one of the most commonly used programs and is derived
from C and C++. Java is a good introductory language and has a lot of online tutorials due to the
popularity of it. Unlike C and C++ it is much easier to create object models. Java is able to
program and change compilers and not have to reformat. It is available on many platforms but is
primarily used on Sun machines.
Lawnmower
The lawnmower is one of the most important components to our autonomous lawnmower
project. Not only does it provide a basic framework for our computer components and electric
motors to be placed on but it also provides parts that would normally not be available to find on
their own.
There are two different types of lawnmowers: electric and gas-powered. Among those
types of lawnmowers are push mowers, reel mowers, and riding mowers. The most common are
push mowers. They are particularly suited for small plots of grass, such as lawns found in
residential neighborhoods. One can usually find a push mower powered by an internal
combustion engine or an electric motor. The push mowers powered by an internal combustion
engine typically have an alternator to produce electricity for the drive wheels. The internal
combustion engine drives the blades under the mower deck. The typical drawback of the gas
mower is the amount of moving parts. There is a larger chance of failure, and the constant need
to oil those parts can become costly.
The electric push mowers come in two varieties: corded and cordless. Each of these
varieties have one main electric motor to power the blades and sometimes two smaller motors to
power the front two drive wheels. Corded push mowers are provided electricity from an electric
cord of a fixed length. These mowers are limited in range and because of this, are usually only
found in the smallest of lawns. Cordless are found in larger lawns and benefit from a battery to
power their electric motors. However, their battery is one of their drawbacks. The batteries
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constantly need recharging and usually only provide enough charge for about 2 hours of constant
use.
Figure 13: Yardworks 18” 12A electric lawnmower
Motors
The lawnmower isn’t the only important aspect of this project. The motor powering the
blades under the mower deck is just as crucial. Like the lawnmower there is a choice between
two types of motors: internal combustion and electric. The internal combustion engine is the
most common but electric motors are slowly gaining popularity. The internal combustion
engines for lawnmowers are typically 2-stroke engines ranging between 50cc and 150cc. The
drawback for them is that the engine produces vibrations and in order to start the engine a
drawstring is typically used. The vibrations from the engine could loosen bolts attaching
important components and if the autonomous mower were to ever shut off the motor then an
external component would be needed to start it again.
The other type of motor is electric. The electric motors for lawnmowers are typically
12V brushless motors weighing about 15-20 lbs. The benefits of the electric motors are that they
run very quietly and they don’t take up too much space on the mower chassis. The one
drawback to electric motors is the power. Usually the more power needed out of the motor the
larger and heavier it gets. Luckily the power needed to turn the blades on a mower doesn’t
require too much power. Using a brushless motor also adds to the safety of the motor. The
brushless doesn’t create sparks like the brushed motors do. The motor can also be precisely
controlled.
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Figure 14: Marathon Electric Brake Motor
Wheels
The wheels and motors that our team has acquired for our autonomous lawnmower are
from the company Sunrise Medical. These were given to Southern Illinois University
Carbondale by Adam Sims senior design team, our predecessors.
There are two spindle, or free moving, wheels that are going to be used for the front of
our design. These wheels are eight inches in diameter and two inches wide. The spindle wheels
will be attached to the front of the lawnmower frame by using a three hundred and sixty degree
spinning attachment that came attached to the wheels.
Figure 15: Acquired Spindle Wheel
The two electric motor wheels are also from Sunrise Medical. At the end of the project,
these will be the drive system for the machine. The same process as a zero turn riding
lawnmower will be applied to make the turning radius of the machine as minimal as possible.
They will be attached to the rear of the lawnmowers’ frame to get the full effect of the zero turn
process. The zero turn lawnmower spins the wheels in opposite directions to turn effectively left
or right. These wheels will be attached securely to the frame to insure that they do not come off
in the process of turning or moving. The dimensions of the powered wheels are: diameter of
12.5 inches and a width of 2.5 inches.
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Figure 16: Motorized Wheels
The electric wheels are powered with Fracmo motors. The brush motors are sealed to
the gear box, which makes the wheels turn at a rate up to 114 RPM. They can withstand up to 24
Volts each, with a minimum requirement of 22.5 Volts. This means that our team will need to
have two 12 Volt batteries attached in series for a single motor to run.
The motor should be wired to a control box that connects to a VSI joystick. The joystick
is the steering mechanism that would allow the lawnmower to turn in a circle or away from an
obstacle. The VSI joystick that is needed is no longer available to the general public. Also, it
cannot be tampered with or worked on due to magnetic sensitive components. The VSI joystick
was the only item that we could not find in the machine shop on campus. Since the VSI joystick
cannot be found or replaced in the foreseeable future, our team has two options: get a new set of
motors and wheels, or splice the wires that would go to a control box and try to manipulate the
motors by changing the polarity of the batteries by using a mechanical and electrical system
coupled with a computer program.
Figure 17: Battery hookup (top) Control Box hookup (bottom)
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Works Cited
Purdie, Tom. Interview. Rachel Parth. 5 October 2011.
Team 94 Saluki Engineering Company Lawnmower-Design Report : 2009. Trevor Parnell, Adam Sims,
Krishna Patel
CWRU Cutter C Technical Report: 2010. Case Western Reserve University, 10900 Euclid Avenue,
Cleveland, Ohio, 44106, USA
http://alternatives.rzero.com/lang.html
Java information. http://en.wikipedia.org/wiki/Java_(programming_language)
C. http://www.eskimo.com/~scs/cclass/notes/sx1.html
C++. http://www.cprogramming.com/begin.html
Visual Basic. http://en.wikipedia.org/wiki/Microsoft_Visual_Studio
GPS Receiver Module.
http://www.parallax.com/Portals/0/Downloads/docs/prod/acc/GPSManualV2.0.pdf
RXM-SG GPS Module w/Ext Antenna.
http://www.parallax.com/Portals/0/Downloads/docs/prod/acc/28505-RXM-SG-GPSModulev1.0.pdf
Northern Arizona wind and sun. http://www.windsun.com/Batteries/Battery_FAQ.htm
http://www.wind-sun.com/ForumVB/showthread.php?t=8228
Wheeled Robot picture: http://news.cnet.com/8301-17938_105-10378593-1.html
Tracked Robot picture: http://defenseupdate.com/features/2008/november/11208_minirobotugv_urbancombatindoor.html
“The AC’s and DC’s of Electric Motors”, A.O. Smith, Retrieved 2009/12/07
http://www.aosmithmotors.com/uploadedFiles/AC-DC%20manual.pdf
http://thelawnmower.info/history.php
“Push for more Efficient Mowers”, Published May 05, 2008.
http://www.metronews.ca/vancouver/live/article/48994