wheelchair

About three years ago I accepted arthritic degeneration of my hucklebone (hips) as an excuse to build a power wheelchair. It’s a dangerous project that could injure or kill me if I’m not careful. Several components, from the joystick MPU to the rear casters, are used in ways forbidden by manufacturers’ fine print, so follow my example at your own risk!

The chair uses two 500W electric scooter motors to drive wheels meant for a go-kart. Tractor-lug wheelbarrow tires would fit (and be awesome), but non-marking wheelchair tires are more politic. A jackshaft adapts between #25 chain for the motors and #35 for the wheels, and allows gearing adjustment up to about 30:1. McMaster-Carr saved the project with #25 sprockets stocked in the right size. The motors and jackshafts are on a sliding sub-frame for independent tensioning of the chain stages.

The motors are powered by two U1-size AGM batteries via a Robot Power Sidewinder speed controller. A Zilog Z8 EncoreXP microcontroller converts the analog output of a game joystick to radio-control-style servo pulses for the Sidewinder. Fail-safe control is vital, so code and test carefully! PIC and Atmel microcontrollers seem more popular, but I’m familiar with Zilog chips, and they’re cheap. At about 10 MIPS, my joystick’s MPU is as powerful as the CDC 6600 mainframe I used in school!

The chair frame is 14-gauge square carbon steel tubing, which I cut and joined with a 4″ angle grinder and 110V flux-core wire welder. (Flux-cored welding is easy enough, but takes some practice; some of my first welds failed.)

The most eye-catching feature of my chair is its seat. Camouflage bass boat seats are just cheaper in my size than wheelchair seats! I added angle steel extensions to the back to make the seat a little deeper. Zipper pouches in the same camo pattern were a lucky find.