simply a series of 5/8 inch aluminum plates bolted to
off-the-shelf go-kart hubs and connected with a one inch
keyed shaft through the bearings in the frame. Each crank
on the crankshaft connected to four pushrods: two going
to each leg that drove the walking gait. Each set of two
legs was connected to its twin and set 180 degrees out of
phase, ensuring that two legs would always be in contact
with the ground on either side of the driver for stability
Electrical power comes from four 12 volt, 12 amp-hour
sealed lead acid batteries, generously donated by Ecopeds.
They were mounted underneath the driver in a series-parallel arrangement yielding 24 volts at 24 amp-hours.
Probably not enough for serious off-road endeavors but
enough to demo, we reasoned. Control electronics were
sourced straight from the wheelchair with the original
joystick mounted ergonomically at the driver’s right hand.
The driver sat comfortably in an old student desk chair
hacked apart and secured to the frame with woodscrews
and a 2x4.
How did it all work? For five guys with no budget and
almost nothing but hand tools, it came together well. It
walked, it carried a rider, and it looked totally bad ass doing
it. We made a splash in the Engineering department and
were even rewarded with the honor of displaying our beast
in the engineering lobby during final exams. Was it perfect?
No. If we were to rebuild it, we have certainly learned a
few things. We encountered a few issues with binding and
interference, mainly from our own loose manufacturing
tolerances. We also discovered that wheelchairs have a very
conservative built-in current limiter that prevented sufficient
amperage from being delivered to the motors. Unless
the batteries were totally topped off, the machine did not
We learned a lot and hopefully managed to inspire a
few young engineers out there to rethink the way machines
are supposed to work, and maybe get them off of their
damn computers. SV
Salvador measures a leg to ensure clearance.
Crankshaft in center. A perfect fit!
Hector testing weight capacity and driver position.
Testing stance and stability.
SERVO 11.2009 57