■ FIGURE 2
But first, I needed a platform.
GET YOUR MOTOR
I was lucky enough to receive a
salvaged power chair from another
member of The Robot Group. It was in
pretty rough shape (Figure 2) with the
chair portion missing, the fiberglass
shell pretty banged up, the speed
controller blown, and the batteries in
need of replacement. But the motors
were still good and the tires were fine.
To rehab the chair, I stripped off
the old fiberglass, cleaned the chassis,
and removed the old speed controller
(Figure 3). I mounted two new MC7
speed controllers and an RCIC2_SC
dual channel joystick mixer from
Diverse Electronics (Figure 4). The
RCIC2_SC mixer allows you to do
skid-steer with a single joystick from
the R/C receiver.
I found replacement batteries
right here in town at Battery
Wholesale.com that has a store front
in Austin so I was able to get the
batteries without shipping charges.
With new speed controllers, charged
batteries, and the Futaba radio in
■ FIGURE 6
■ FIGURE 3
■ FIGURE 4
place, I was ready to try out my new
TESTING ... TESTING ...
IS THIS THING ON?
I switched on the power for the first
time and carefully pushed the
joystick forward. The motors made their
whirring sounds but the chassis sat
stock still. A bit of investigation showed
I had not engaged the wheels! Seems
this type of power chair has mechanical “free wheeling” levers that need to
be placed in the “run” position or the
motors don’t engage. With the levers in
the run position, I again moved the
joystick and the chassis slowly rolled
across the floor! Success! I then tried
running it a bit faster and was pleasantly surprised to find the MC7s made no
buzzing noises when PWM’ing the
motors. They do have relays that click
when the motor direction is changed,
but the controllers are otherwise silent.
I thought the refit was complete
until a fellow robot group member
discovered that the motors on this
chair have electric brakes that need to
be energized to release them! Once
we rigged up the wires to the electric
■ FIGURE 7
brake leads on the motors, my battery
life and top speed improved dramatically. So, now I had a powerful mobile
platform but ... what could I do with it?
BREAK IT DOWN!
Because of the diversity in our
group membership and the audiences
■ FIGURE 5
■ FIGURE 8
October 2007 85