Shannon Lee, Robert Rayson, and
Brandon Greenlaw, University of Ottawa
goal of our ELG3336 project was to construct a robot that could
be used to remotely survey an area at a relatively far distance.
The vision for this project was that it would be used by police
and security personnel to get a visual of areas far too
dangerous for them to be present in; particularly in the event
of a terrorist attack.
For this vision to become a reality a more
compact and durable version of our prototype would be developed
such that it would be better accustomed to a hostile
environment. This project consists of two sub-sections: the user
interface and the robot itself. The user interface consists of a
physical remote controller, transmitter, LCD screen and a 7.2V
battery pack (6 AA batteries) to provide power to said
The electronic components of the robot are an
Arduino microcontroller, motor-shield, receiver, camera, four DC
motors, two servo motors, LED lights, a 3000mAh battery pack to
power the Arduino and an additional 7.2V battery pack to provide
power to the remaining components. The structural components
were designed in Solidworks where the baseplate and wheels are
made of ⅛ inch MDF particle board and laser cut while the
mounting components were 3D printed. When operating the robot
the user has the option of driving the robot as well as pivoting
and rotating the camera independently.
The footage that the camera captures is
wirelessly transmitted to the LCD screen which the user can use
to confidently control the robot at a far distance. Initial
testing in the SITE building at the University of Ottawa
resulted in the robot being able to travel approximately 100
meters from the user before losing signal. Note this building is
largely made of concrete so expected range is to be much higher
if used outside or in different buildings.
2 Servo Motors
4 DC Motors
2- 7.2V Battery Packs (6 AA Batteries in series, handmade)
1- 3000mAh Battery Pack
1- 4” LCD Screen
1 Remote Controller
4 LED Lights
PLA Plastic (3D print material)
⅛” MDF Particle Board
8- M4x24mm hex bolts with washers
8- M3x30mm hex bolts with washers
Makerbot Replicator 2 3D Printer
Epilog Laser Cutter
Every design needs a strong foundation therefore
the first step in our design process was to ensure that the base
platform was both large and strong enough to support all
components as well as making sure that the wheels were properly
secured to the dc motors.
Designing the baseplate was simple. The only
criteria was that it had to have a large enough area to support
the components and that there were holes cut such that both the
motor mounts and the camera column in the center could be
secured. The schematic (140mm x 220mm) was created on solidworks
and laser cut onto ⅛ inch MDF particle board. Reasoning for
choosing MDF was that it was strong enough to support the
components, while being cost effective and easy to cut.
Top view of baseplate model (Solidworks)
Designing the motor mounts was a bit more of a
challenge as it had to secure the dc motor while also being
fixed to the baseplate. As seen below in Figure 2, the solution
was to dimensionalize the mount around the DC motor and then use
nut-bolt pairs to fix the motor to the mount and to then fix the
mount to the baseplate. Due to the complexity of the mount, all
four were 3D printed using Makerbot technology.
Motor Mount (Solidworks)
For this robot we wanted the wheels to be large
enough such that it could move past small obstacles with ease
therefore we modelled a 90mm diameter wheel (seen in Figure 3,
left) and lasercut 4 of them on ⅛ inch MDF particle board.
However due to the large ratio between the wheel diameter and
the bore diameter the wheels wobbled extensively. Therefore an
additional attachment was designed (Figure 3, right) where the
small end was press fitted to the motor axle while the wider end
was glued to the wheel thus reducing said ratio and increasing
stability in the wheels.
The camera orientation is an important feature of
the robot where a user is able to control the robot without
physically seeing it. To ensure a good range of view for the
user, the camera can rotate 360 degrees horizontal to the
ground, and 180 degrees in the vertical plane with the use of
two servo motors controlling each rotation. With the use of
these two functions, the robot has a full range of motion with
zero blind spots. Every element comprising the camera mechanism
is an original design and 3D printed.
The biggest challenge was to overcome the amount
of friction between the axle that rotates the camera 360 degrees
and the MDF robot base plate. Originally, two spur gears was
used to function the 360 degrees range of view where one of the
gears is attached to a servo motor. However, since the camera
mechanism was supported on one end of the base plate, it
produced a large moment around the end of the camera mechanism,
causing a large friction force against the base plate and camera
axel. This can be shown in Figure 3. To overcome this problem,
the camera mechanism needed to be supported on the base plate
from the middle of the camera mechanism for much less friction.
Figure 4 shows the changes from the original camera model where
a 3D printed bracket (black) was added to the middle of the
camera mechanism. This reduced the amount of friction
dramatically where it allowed the camera mechanism to run more
smoothly and having the servo motor do less work. To reduce even
more friction, the gears were moved more towards the middle of
the mechanism. The gears have been changed from spur gears to
bevel gears for less gear slippage and more space efficiency.
Regarding the mechanism for the 180 degree range
of view, shown in Figure 5, the entire linkages were 3D printed
and are an original design. The linkage allows for the camera to
look directly downwards and directly upwards. With the use of
the 360 degree movement from the second servo motor, the robot
is able to see every single degree around itself without any
blind spots (with the exception of underneath the base plate).
This full range of camera orientation is particularly useful for
single level exploratory tasks such as hazardous areas. The
camera is able to function in completely dark or illuminated
Power Distribution System
The power distribution system employed by our
robot is somewhat complex. The arduino uno is powered by a 5v
usb battery pack, while the rest of the robot is powered by a
7.2v battery pack which consists of 6 AA batteries wired in
series. We decided to isolate the power source for the arduino
from the rest of the robot to ensure that the arduino was
provided a clean, consistent power signal. Any fluctuations in
the power system caused by the motors, transmitter, or receiver
could have detrimental effects on the operation of the arduino
if the power sources were not isolated like this.
The two servo motors required a steady voltage of
5V, while the motor shield, video transmitter, and camera
required voltage in the range of 7.2V. As such, a step down
transformer was used to drop the battery voltage down to 5V, as
seen in Figure *. The breadboard seen in the same Figure was
also used to form several connections in parallel between the
different 7.2V components and the battery pack. Finally, as seen
in the same figure, the breadboard was also used to house the
connections and resistor required to step down the 5v signal
from the arduino to a reasonable voltage to drive the LED light.
The power distribution system at the base station
is relatively simple in comparison. A 7.2V battery pack,
consisting once again of 6 rechargeable AA batteries, is
connected in parallel with the power inputs for the monitor and
DC Motor Control:
Four DC motors are used to move the robot
relative to its surroundings. They can be seen in Figure 6.
These DC motors are driven through an Adafruit Motor Shield V3.
This motor shield allows us to power the motors separately from
the arduino, the arduino provides the instructions for the motor
but the actual power is provided from the 7.2V battery pack. It
also allows us selectively set the speeds of each motor as well
as selectively driving them in forwards or reverse modes.
Controlling the motors was accomplished through the adafruit
motor control arduino library that we included in our code, for
more details on this please see the “code” section near the end
of this report.
The 4 DC Motors
An Arduino Uno R3 microcontroller acts as the
“brains” of the robot. The code that it runs is relatively
simple, it essentially just listens for commands, interprets
them, and executes them. This process is run as a simple loop,
repeating several times a second.
When the remote is turned on, it transmits
pulses along six different channels many times a second. Each
channel corresponds to a certain input on the remote, for
example channel 2 refers to the lefts stick’s vertical axis.
Whenever these inputs are modified, the pulse width
corresponding to the modified input will change as well. These
pulse widths range from a value of 1000 to 2000.
The arduino code for the robot begins with the
instruction to “listen” to the outputs of the radio receiver,
seen in Figure 7. Interestingly enough, the receiver only
outputs data along certain time intervals, it essentially
operates at a unknown frequency. As such, it was critical to
ensure that the arduino and receiver were operating in sync,
that is to say that the arduino “listened” while the receiver
output data. We synchronized the arduino and receiver mainly
through trial and error, adding and modifying delays present in
our code until the arduino consistently received instructions
from the remote. There most certainly would have been superior
ways to approach this issue, for example we could have likely
employed a conditional loop such that the arduino would wait
until it had received the data it required before continuing
with the rest of the main loop.
The RC Receiver
Once the arduino has received all of the data
that it requires, it is then necessary to translate this data
into commands that the outputs can accept. For example, the 180
degree servo motor used in the camera orientation assembly
requires an input value between 0 and 180 to determine what it’s
position should be. As such, the arduino code translates the
value on the relevant channel, which ranges from 1000 to 2000,
to a corresponding value from 0 to 180 degrees.
Once all of the above commands have been
completed, the arduino then repeats them in order. This process
occurs with a relatively high frequency, resulting in no
perceptible lag between an input change (moving one of the
sticks) and the desired output (motor movement . led brightness
change). The code that the arduino runs can be seen in the
“code” section near the end of this document.
The video system for our project consists of four
main parts. They are the camera, the video transmitter, the
video receiver, and the monitor, The camera on the robot outputs
an analogue video signal to the video transmitter (also attached
to the robot), which transmits this signal at a frequency of
approximately 2.4 GHz. This wireless signal is then received at
the base station by the video receiver, which then outputs the
analogue video signal over composite video wires to the monitor.
As long as all elements of the system are operating nominally,
the monitor will display whatever the robot’s camera is directed
//Robot Firmware V4.1.2
//Written by Robert Rayson, with some inspiration
drawn from several online resources,
//including "RC PulseIn Serial Read out" by Nick
Poole, and the