Noot / Erwt Notes

Note #1 Tuesday 06 September 2011

I’m going to try keep a log of the Noot design process as a reference for why I made unwise-in-hindsight decisions.

The Noot is effectively a Foxbot v2. The goal is a small, cheap, easy to produce robot, avoiding the USB hassles I had with the original Foxbot. It should be easy to write code on and provide some method for hardware expansion

CPU / Language

My original plan was to try make something minimal - maybe a 4-8KB ATTiny - that would be programmed in Forth (the interactivity/REPL is important). But given the size-constraints imposed by the motors, it seems the only feasable route would be SMT components, at which point a small ARM seemed like a better choice than an AVR. I can also fit the FT2232 for a JTAG-USB interface (like the Stellaris dev boards), so I’ll be able to run Pindakaas. The FT2232 avoids any USB difficulty as there are drivers available for all the platforms (often without needing to download anything extra). Actually, I might build a separate robot with the same motors, but using an 8-14 pin ATTiny, just to see how it’d work. I must investigate the ARM choices.

Motors

The design is based around the Pololu plastic gearmotors and 32x7mm wheels. These are both cheaper and smaller than the metal gearmotors and wheel combo used on the Foxbot. I’ll lose the ability to encodered-feedback on the motors, but I never used that on the Foxbot anyway. I’m going to order a pair of motors and wheels for measurement and testing. The L-shape gearbox is convenient for the physical layout as when arranged in a mirror configuration, it leaves space in the centre for a possible pen, while still being smaller than the Foxbot.

Power

The motor+wheel combination results in a bot of about ~75mm diameter, which gives an internal square of 53mm to a side. AA’s are 14.5x50.5 and AAA’s are 10.5x44.5. That means 3xAA or 4xAAA. But it’d be nice to leave space in the middle for a pen to do turtle-style drawing. That reduces it to 2xAA or 2xAAA. Which gives 2-3V for the main supply.