Scrap 8.2 by Devin Ostrom

Scrap was a 6 wheeled 208 pound robotic entrant into the TLC's 
Robotica Competition.  It was built using scrap
materials found in my lab.  The controller 
was based upon 2 PIC 16F84 controllers; one PIC for each 
motor side.  Each PIC was programed to accept a custom
data packet and execute a 
closed loop PD controller with velocity and position inputs.  
This allowed the robot to steer in precisely
controlled pathways and execute preprogrammed 
movements (peroet to the left/right, turn 90/180 degrees, etc)   
There is also a slashing/lift fork on the front
with a lifting capacity of 200 pounds and
a swinging battle hammer (18 pounds) on the rear that is 
activated by centrifical forces during a spin move.  The
radio link was based upon Abacom Technologies 
RTF3-433 miniature FM TX/RX data modules (range 500 ft 
line of sight).  The joystick was a gutted "Cyborg 3000
3DOF" joystick with another PIC 16F84 controller 
set to scan all inputs and relay the data packet to the radio module.
The drive system was based upon two Ivacare electric 
wheelchair motors chain linked to 3 wheels per side.  The
middle wheels were lowered 1/5 inch from the outside
wheels in order to reduce drag during "skid steering".  
This worked out quite well as we could "spin" the robot
upto 45 RPM.  The frame was made from 3 inch 
angle iron 1/4 inch thick welded into a "U" frame where the 
wheel stem and motors were bolted to.  The lifting
forks were made from 1.5 inch angle iron with a 
500 pound capacity linear actuator.  The slashing forks are 
made of hardened steel plate ground to a knife edge.
Design time 3 weeks, construction time 8 weeks (including 
time for electronics), total cost $500 Canadian (not
bad).

The biggest problem with this system proved to be with the 
off-the-shelf components.  The joystick grew sloppy with use 
and I am planning on replacing it with a custom mechanical 
joystick interface.  The radio data links are too low powered 
and are easily swamped by EMI.  I will also replace the control 
electronics with a higher level PIC and utilize thier
associated hardware based PWM outputs.  A second 
generation robot is also being designed and the autocad 
drawings should be ready by December.  

Email: dostrom@ryerson.ca


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