The Bug is similar to last years design (Busy Lizzie), with the general idea of producing a lighter weight mouse (12 ozs) which will aid acceleration and deceleration when running and turning.
The
nose wheel is steered with a modified R/C servo. This wheel is also coupled to an optical reader (cannibalized
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 80C320 running
at 20Mhz.
Power
supply is 6 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 etc.
Motors
are switched and reversed using 2919 bridge motor driver and braking uses
resistors across motors switched in by Mosfet relays.