I fabricated a quick two-wheeled robot chassis tonight, which I’m calling TriloBYTE because of the rounded front. It’d look more like a Cambrian-era Trilobite if I had the USB cable trailing out the back, but the scuttling motion is definitely Trilobitian.
The chassis fits in a 7″ diameter circle, and is made from 1/2″ thick red HDPE cutting board, scroll saw cut following my chassis template (PDF or SVG). I always draw up a template in Inkscape and print and glue it down before cutting, drilling, or milling–it’s so much easier to build stuff if you already know where everything is going!
It drives nicely when powered by two tiny Pololu 1:100 gearmotors and 42x19mm wheels. The motors drop into milled slots in the chassis, and are held down with 1/2″ pan head self tapping screws (with 3/32″ holes predrilled).
The motor controller is a sparkfun ardumoto shield, which seems to work fine when powered only by the Arduino’s 5v line. With bigger motors I’m sure I’d be stressing the USB connection, but these tiny motors work fine–the stall current is only 200mA or so.
I definitely need mechanical strain relief on the main USB cable, because I’m finding myself putting a lot of stress on it just bumping around. You could definitely argue for putting the Arduino in backwards, so the USB cord trails behind. Surprisingly, the USB cable doesn’t seem to drag the robot around too badly, at least until it tries to climb its own cable. The motors definitely have enough power to hop the cable, but not with the open-loop PWM setup I have.
The cat seems fascinated by it!
Next up: some sensors, and real control software. Using Firmata to test out new hardware is sure easy!