"R4" (Reconfigured Robot Rally Roomba)

"R4"
(Reconfigured Robot Rally Roomba)
Specifications
Chassis:
Processor:
A cannibalized “iRobot Roomba” (model: 4110) vacuum cleaner. All Roomba
components were taken out except the
motors, H-bridges, wheels,
encoders, and 4 cliff sensors.
Arduino Atmel Mega 1280
Digital I/O:
54 (14 PWM)
Analog I/O:
16
Weight 5.6lb
Diameter 14”
Height 6.25”
Power 16 AA batteries.
Max speed (calculated) = ((2.56”*pi)* 138rpm)/60 = 18.5 in/sec
1st year competing R4
Outfitted with the following additional components:
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Four Infrared Proximity Sensors Short Range - Sharp GP2D120XJ00F
Two Ultrasonic Range Finder - MaxBotix LV-EZ3
Homemade infrared line following sensor array (5 sensors)
Deployable plow
Event
Sensor or component utilized for event
Beacon Killer:
Pololu IR beacon transceiver pair.
Beacon Killer w/obstacles
Pololu IR beacon transceiver pair.
Four Sharp infrared proximity sensors for object detection
Dead Reckoning:
Onboard Roomba incremental encoders
Line Following:
5 homemade IR line sensors
Bulldozer:
4 onboard Roomba cliff sensors.
4 Infrared Proximity Sensors for object detection
Expandable Plow wings
The build report can be downloaded at www.Atlanta-Robotics.com
This project was to build a robot to compete in the Atlanta Hobby Robot Club’s (AHRC) “Robot
Rally” Polyatholon competition. The iRobot Roomba platform was chosen partially because of cost and
time restraints but most of all to provide amateur robot builders with a base model and tutorial to help
get them off the bench. Since the Roomba is basically a motorized chassis hopefully it will remove the
intimidation that some DIY’ers might have when wanting to build a similar robot. This Roomba model
4110 was bought at a garage sale for $20. You can find several deals like this on used Roombas at online
auction sites pretty cheap once the original owner’s battery no longer holds a charge and they are tired
of it. I like to replace the battery with a bank of AA’s anyway, plus the empty pocket where the Roomba
battery went is a great place to put a set of line sensors.
The Polyatholon the R4 was designed to compete in the following 6 events:
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Basic Line following
o A basic oval shape made with ¾” electrical tape on a white foam board. Turn radiuses
are no less than 6 inches. Lines will be at least 8 inches from the edge. A time limit of
90 seconds will be imposed. Failure to complete the course within 90 seconds will result
in a score of zero
o Fastest time wins
Advanced line following
o Course will have intersecting lines and 90 degree turns. Non-intersecting lines will be
spaced apart greater than 8 inches. Intersections will be 90 degrees. The line the same
tape used in the basic line following event and will be at least 8 inches from the edge. A
time limit of 90 seconds will be imposed. Failure to complete the course within 90
seconds will result in a score of zero
o Fastest time wins
Bulldozer
o Push 5 objects off a table in the least amount of time without driving off the edge. The
objects to be pushed are 3.5” long sections of 3.5” OD white PVC pipe standing on end.
The surface is a 2.5’ x 8’ folding table 3.75 inches above the floor. There will be no line
marking the edge. Robots must detect the 3.75” drop-off to avoid falling off. Robots
may use optical, mechanical, sonar, or other sensors to detect the edge. There is a 5
second delayed start. Robots start behind a line that is 18 inches from the end of the
table. All objects are on the other side of the line. Time starts when the robot moves
and stops when all objects are pushed off. Time limit is 90 seconds. If the robot runs off
the table before pushing off all objects the time defaults to 90 seconds. A time penalty
of 10 seconds is imposed for each object left on the table after time expires or the robot
falls off.
Navigation by dead reckoning
o Travel 3 legs of an equilateral triangle in a clockwise direction and arrive back at the
starting point. Scoring is based on how close the robot is to the original start position.
The robot must accurately measure distance traveled and angle of turns to succeed.
The triangle sides are 4 feet. There are no lines. Robots must touch imaginary 8.5 inch
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diameter circles at the intersections of the 4’ sides. The contestant must define the
reference point on the robot which will be placed over the starting point and used to
measure the offset distance when finished. 2 minute time limit.
Beacon Killer
o Travel 10 feet to make contact with a beacon from a random start orientation in the
least amount of time. Contestants may supply his own beacon or use the Atlanta Hobby
Robot Club’s Cube Quest white light beacon. The robot will be placed 10 feet from the
beacon pointed in a random direction. All contestants will be placed in the same
direction. Robots will have a 5 second delayed start. Time starts when the robot starts
moving and ends when it touches the beacon. Robots have a maximum of 60 seconds
to complete this task.
Beacon Killer with obstacles
o Travel 10 feet to make contact with a beacon from a random start orientation in the
least time without moving obstacles. A time penalty will be imposed for each obstacle
moved. Five to twenty objects may be placed in the area between the robot and the
beacon. They will be at least 2 feet apart, edge to edge. The objects will be 3.5 inch
sections of 3.5 inch OD white PVC pipe standing on end. The position of each objjext
will be marked with a small marker. Markers will be about 3 inches in diameter.
Moving an obstacle more than ¼” will expose the marker. A 10 second time penalty will
be applied for every marker that is exposed after the run. Robots have a maximum of
90 seconds to complete the task.
This build report, videos and other related documents can be downloaded at my website at
www.Atlanta-Robotics.com. Since pictures get the message across so much better than descriptions I
have tried to take pictures of everything. This document is a work in progress and will be updated soon.
Without any further preliminaries, let’s start talking Roomba.
R4 OVERVIEW
DISSASEMBLY OF THE ROOMBA AND CHASSIS CONSTRUCTION_______
First off, here is a good video to get started with the disassembly of an iRobot Roomba
http://www.dinofab.com/roombahack.html
All of the vacuum components were taken out of the bot. All unneeded wiring was clipped off
and some plastic had to be drilled and cut to get the chassis ready for its new purpose. The Roomba
motherboard was used only for motor control. The only wires I left on the board were the motor power
wires. I then soldered on the control PWM wires to the transistors on the board that control the
motors. This procedure is shown in the above link. Here is a very helpful hint if you do not cannibalize
stuff like this often. DO NOT clip wires off right at the connector, leave at least 1 inch of wire remaining
in case you made a mistake and need solder them back together. Even better if you can just disconnect
the wires and zip tie them out of the way even better. You can see in the following pictures that I did
just this until I knew I was not going to need them.
Now that everything is off I needed a new floor plate platform to put all of my components on. I
had a sheet of ABS plastic that would work perfect for this. The CAD drawing I made for this plate is
shown below. I also had to clip off several plastic bosses and tabs for the correct fit. The CAD .dxf file
can be downloaded from my website (www.Atlanta-Robotics.com) along with this document. Now with
the plate installed I can drill and mount anything I want at my discretion.
R4 floor plate
Removal of tabs to accommodate new floor plate
Removal of plastic to accommodate new floor plate
Finished floor plate installed
I used two ping pong balls as front and back slider wheels. Ping pong balls are perfect for
something like this. They are cheap, easy to cut and mount, have low friction, and pass over small
obstacles without any issues. Try and mount these in the center of the bot to avoid any left or right
drag. The batteries are mounted on the bottom which is a perfect place to put them. This allows more
electronic room on top of the bot.
MOTORS AND WHEELS_______________________________________
The motor power comes directly from 12 AA NiMH batteries in series which supplies 14.4V, the
original Roomba battery voltage. The 5volt TTL power for the rest of the electronics comes from
another set of 4 AA Alkaline batteries which gives 6V.
The pictures above show the turquoise SPST limit switch to detect when wheel falls off an edge.
The Roomba wheel swings out from the bottom of the chassis if it is not on the ground. These were not
used on the R4 though they are still available if needed in the future. They can be easily wired up to an
input of the microcontroller.
Drive motor in chassis shown on left and removed from chassis shown on right.
Drive motor cover taken off exposing encoders
Here shows the 42 tooth encoder wheel and drive belt cover removed from the drive motors.
You can see the o-ring drive and encoder wheel. The IR LED transmitter and receiver are shown in each
picture. The brown and blue wire pair goes to the transmitter and the gray and black wires go to the
receiver. They are facing each other when assembled and as the encoder wheel turns it breaks the light
beam. This signal is captured by the Arduino Mega inputs using an interrupt routine. Make sure there is
no dust or debris in this area since it will affect the encoder
Since the encoder wheel is coupled very close to the motor and before the gear box it spins
much faster than the wheel, giving is much more accuracy as an odometer or speedometer. The pulley
on the motor was measured at xxxx and the pulley at the encoder was measured to be xxxx. This gives a
reduction ratio of xxxx. Access to the gear box is on the other side of the motor and is shown below.
Reverse side of wheel assembly with cover on and off.
The other side of the motor has a cover shown above on left. Be careful taking it apart, there
are small pieces that can fall out. Under the wheel shows the housing for the gear box. It is a planetary
gear type as shown in the following two pictures. The gear ratio is xxxx and coupled with the belt gear
ratio equals xxxx.
Wheel removed
Planetary gears of the drive wheel
Above shows the circuit used for capturing the encoder pulses. Pin 20 on the Atmel
microcontroller is used for interrupt number 3 and pin 21 is used for interrupt number 2. The snippet of
code below should give you insight as to how it is captured. For the navigation by dead reckoning event
the encoders are how the bot knows where it is. The basic routine for the dead reckoning event was to
go straight for a certain number of encoder pulses, turn a certain number of pulses, go straight, etc…
Because of the sloppy wheels the R4 did not perform very well in this event.
attachInterrupt(2, ENCODER_PULSE_L, RISING); // interrupt #2 is on pin 21, watch left encoder for rising pulse
attachInterrupt(3, ENCODER_PUSLE_R, RISING); // interrupt #3 is on pin 20, watch right encoder for rising pulse
// ENCODERS //
void ENCODER_PULSE_L(){
count_l++;}
void ENCODER_PUSLE_R(){
count_r++;}
Incremental encoder signal.
Below explains how I lined up the wheels. The alignment is important for the “Navigation by
Dead Reckoning” event. If the wheels are not straight the bot will veer to one side. I used a couple
squares and laser level for this procedure. I turned the bot upside down and got it as square as I could
with the drywall square I taped to the table. Then I used another smaller square to slide the laser level
from one wheel to another. Once the wheels were lined up I used hot glue to secure them in place.
The Roomba wheels are naturally too loose and wobbly so there is a great lack of accuracy. More
development will come later on this.
CLIFF SENSORS______________________
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The cliff sensors that come with the Roomba are used for the bulldozer competition. There are
four sensors on the front of the Roomba. These sensors are just an IR emitter and receiver. If the
sensor does not see anything then it is at the edge of the table and must stop or back up. The Eagle
schematics are shown below of how I wired them up to the Arduino microcontroller. I also acid etched a
board for this. After drilling some new holes for the wires to go through I put the new board I made
where the original Roomba battery went, this is a nice pocket to put items like this. This Eagle file can
also be downloaded from my web site. Here a helpful hint: use a digital camera like to one on most cell
phones today and look at the IR LED to see if it is on. Most cameras can see higher frequencies than our
human eyes can see. You can test this out by aiming a TV remote at you camera and pressing any
button.
Schematic of cliff sensor array
Eagle board layout on left and etched sensor array on right
Cliff sensor bar removed from Roomba
Cliff sensor removed from sensor bar.
Sensor array shown on Roomba
LINE SENSORS______________________
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Good line tracking links below.
http://www.ikalogic.com/tut_line_sens_algo.php
http://www.chibots.org/?q=node/339
The line tracking sensors used were made from simple a simple IR LED and IR phototransistor.
The 5 pink colored LEDs emit the infrared light down at the floor and the 5 dark LEDs sense the
reflections. The emitting IR LED was from Digi-Key (PN# QED223-ND) and receiving IR phototransistor
was also from Digi-Key (PN# QSD123-ND). The receiver is usually the dark one because the dark plastic
blocks ambient/visible light and the infrared light is able to pass through this type of plastic and
triggering the light sensitive transistor inside. Aim you TV remote at a digital camera or cell phone
camera and you can see the IR light passing through the black plastic.
Line Sensor Board
Below is the Eagle schematic of the line sensor array. When the LED is over the black line the
signal is XXXXX when it is over the white foam board the signal is XXXXX. The code used for determining
where the line is under the bot is based off of the “Centroid Algorithm” developed by Kirk Charles of the
Atlanta Hobby Robot Club.
Line Sensor Array Schematic
R4 competing in advanced line follower
BULLDOZER________________________
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The description of how the robot does not drive off of the table for this event is described in the
Cliff Sensor section above. Since the Roomba is round it does make for a good plow so plow wings were
added for this. The rules for this competition state that the bot must fit within a 12”x12” box or a 14”
circle but arms or manipulators can extend out after the event starts. The arms and bot must fit within
an 18” circle at this point. The plow wings were Aluminum pieces of sheet metal attached to some
hinges. A torsion spring was used to keep them extended while plowing.
R4 with plow wings extended
The plow wings were held in place by a cotter pin tied to a rotary arm motor with some
fishing line. The rotary arm motor is in the center top of the bot and rotates back 180 degrees
and pulls the pins up allowing the plow wings to deploy. The motor arm moves fairly fast so I
decided to use PWM so slow it down. This motor is controlled by a Toshiba TA8050P 1.5A
MOTOR DRIVER WITH BRAKE FUNCTION chip. This is a very simple H-Bridge on a chip. I send it
a 70% PWM signal to the direction 1 pin once the event starts and then on pin 2 to reset the
motor when I change modes for the bot.
Plow wings in action for the Bulldozer event
BEACON___________________________
_________________
I used the Pololu IR Beacon Pair (PN# 702) for the “Beacon Killer” event. The pair consists of two
of the same units and can be used for two robots to avoid or find each other. Each module has six IR
pulsed emitters (56kHz) and four IR receivers. The one placed on R4 was used solely as a locator and the
one placed on the D-cell battery pack was used solely as a beacon. The beacon locator only has the
capability to determine if the beacon is located forward, aft, port or starboard from the bot. The beacon
was placed at the highest point on the bot so nothing will get in the IR transmission path.
http://www.pololu.com/catalog/product/702
The two Maxbotix sonar sensors on the front of the bot are for long range path planning during
the “Beacon Killer with obstacle avoidance” event. The four IR sensors on the front are for short range
avoidance of obstacles.
Beacon locator on left and beacon on right
I don’t think iRobot will be able to help me with my Roomba anymore.
To add: pics of 14” and 18” circles with R4 within specs.
DIP switch modes.
Gear ratios
Test top speed