I have been mousing for
about 6 years and have managed to collect a couple of
cheeses. I started with tricycle stepper motor designs
but now favour front wheel steered DC motor arrangement.
Last year's machine - Busy Lizzie - came second at Exeter.
The Bug is similar to last years design, with the general
idea of producing a lighter weight mouse (12 ozs) which
will aid acceleration and deceleration when running and
The nose wheel is steered with a modified R/C servo. This
wheel is also coupled to an optical reader (cannibalised
from a PC mouse) which produces 34 pulses per wheel revolution.
This is effectively doubled by sensing both the leading
and trailing pulse edges.
The rear wheels are driven by a pair of old Futaba miniature
servos with gear train modified and pot removed.
The computer is a very small unit, EM320 by Devantech
using a Dallas 8OC320 running at 20Mhz.
Power supply is 5 NIMH cells 2/3 AA size using 2930 low dropout
regulators to provide separate 5v rails for computer and servo.
Uses infra-red sensing over the walls - rows of 5 sensors each
side with outer/inner pairs coupled together plus one front
sensor to check for front wall (7 points to read). The software
provides the steering pulse (about 1mS) every 15mS and during
this period all other repetitive functions are executed - sensors
read, update wall map, solve maze algorithm, motor on pulse
To keep currents low the 11 sensor emitter diodes are in series
and are therefore pulsed simultaneously for just long enough
to read the 7 sensor outputs via an addressable analogue switch
(405 1). The 20v power supply for the emitters is a miniature
5 to 15v converter with limiting resistor. Motors are switched
and reversed using 2919 bridge motor driver and braking uses
resistors across motors switched in by Mosfet relays.
Current build state - hardware virtually complete but untested.
Produced and maintained by Wayne,
for Royal Holloway, University of London ©1999 - 2004