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Robomower Part 4 - Wheelchair Teardown

Today was the day to tear down the Invacare Torque SP, and see what parts could be used in the construction of the Robomower.

The Invacare Torque SP

The Invacare Torque SP as it was the day it arrived.

In an ideal world, I would be able to simply sling the lawnmower underneath the wheelchair, hook up all the electronics and controls, and away I go. Unfortunately, that just ain’t gonna happen. A contemporary electric wheelchair is intended to haul a person on the top of it, and all the little bits that make it go (batteries, motors and controllers) are all tucked as neatly as possible underneath. On the other hand, a robotic lawnmower has lots of room on top, and needs a lot of space underneath for the actual lawn mowing parts. So we clearly have conflicting design goals. Nonetheless, I was determined to use as many parts from the original wheelchair as possible. The first parts to go were the seat cushion and backrest, since I knew I would not be using these. Once those were off, I saw something beautiful: A large, flat platform that looked to be just the right size for holding batteries, controllers, all kinds of cool stuff like that.
Torque SP sans cusion and backrest

Invacare Torque SP with cushion and backrest removed. Lots of real estate for batteries and electronics!

The next idea I has was to swap the motors right to left, and turn them around, thus freeing up some space underneath. This, of course, required removing both motors. Anyone who cares to do this, here is a bit of advice: take the wheels off first. the motors are held onto the swingarms by four 13mm bolts. you can remove them with the wheels in place, but it will be whole lot more effort than it takes to just pull off the four little lugnuts holding the wheels on.
Lugnuts removed

Remove these lugnuts and the wheel before trying to remove the motor!


See? WAAAYYYY Easier!

Of course, I figured this out after I got three of the four bolts off of the first motor. The second one went a LOT more smoothly and quickly! Once the motors were off, I investigated the possibility of simply turning the motors around, so the large protrusion went backward, away from where the mower would be. Alas, the design of the swingarm prevented this, as the shock absorber mount was precisely in the way.
Swingarm Detail

Swingarm Detail - The motor won't fit on backward :-(.

Okay, so it looks like the swingarms have to go. I was really hoping that the motor mounts would be usable, but it looks like I’m gonna be drilling some holes in steel… The front half of the swingarms are held in by a single 19mm bolt on either side, hidden under a dust cap.
Swingarm Bolt

This is the single 19mm bolt that holds the front half of each swingarm on.

The back half of the swingarms are attached to the shock absorbers by a through bolt. After removing these, the swingarms fall free. The shocks are held into the frame by a couple of bolts, which also hold in the shipping hooks at the back of the frame members. So basically, the back half of the wheelchair frame will not be usable as is for the Robomower. The front half is still questionable as well. It may turn out that making a completely new frame from angle iron might be the best way to go. In any case, the ABS battery case and the battery case frame are very usable, as is the platform that supports the seat cushion.
torque sp frame front

The front of the Torque SP Frame: This might be the only part of the frame that is usable for the Robomower project.

I really like those casters, and the color of the tires matches the drive wheel tires perfectly. As the pictures reveal, however, the tires have some serious wear, and chunks are missing, so there may be some good reasons to replace them. They mount in a tube, which would be great if the front frame section gets re-used, but the Harbor Freight versions are mounted to a four-bolt plate, which would actually provide some structural reinforcement if I end up fabricating a new frame from steel angle. So, at this point, I called it a day and packed everything back up into the garage. More later!

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