My Home-Built Power
Wheelchair By Marcus Brooks
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. ;
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.
Marcus Brooks is a technical writer in Austin, Texas.
Photograph by Marcus Brooks
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