Hi Friends! So first a brag. Lucked out and scored a used electric wheelchair, complete and intact, 12 years old and all runs well, for about 1/10 retail. I've had my eye out for almost 10 years for a deal like this for robot builds; in the past I've simply cobbled my own together out using various means, with good but not electric wheelchair good results.
So here's the thing: I am going to build a modular death dealing (Nerf) Hallowe'en robot that will see very limited locomotion (basically my driveway) and the way I've designed everything to do the machine vision, lights, audio and arm cannons is built in a modular torso that will be affixed via custom metal mount to the wheelchair base, that will replace the existing seat.
The reason for doing it this way is this: I don't want to actually hack this wheelchair as in I don't want to modify it in any way that would prevent it being used as a wheelchair for someone in the future. After a Hallowe'en or two of using this and doing this build with my kids so they learn, the intention is to donate the wheelchair to the Assistive Devices Program at the March of Dimes, since they were so great in helping my brother when he needed help before he passed away a couple years ago. Sorry to be glum for a sec here, friends, I really miss him.
ANYWAY, the question here is mechanical in nature. I wish to do nothing to change the control mechanism, a factory equipped joystick, I mean AT ALL. Hacking this would make it of no use to MofD in the future for safety reasons. It is zero-turn radius, differential drive. Two mid mounted wheels (drive wheels) and four casters (not powered), two up front and two in back.
I will control it using servo(s) externally mounted and temporarily affixed to the joystick and I have no gift for linkages, servo brackets, that kind of thing. Solving how to link a standard servo or two to the wheelchair joystick has me at a loss, this is the help I'm asking, please. Here's what the control console/joystick looks like. Thanks, friends.
That tells me you have NO shop to make or machine the needed parts. So why do you expect to be able to buy exactly what you need? Are you considering using a 3D printer to make the plastic parts? Could be done.
I would imagine that the joystick is a replaceable part and that it therefore could be removed. If so, perhaps a temporary hack could be achievable, assuming that you can discover the communications protocol.
That's correct, Paul. In my RC hobby, I have always bought linkages and servo brackets that fit the base chassis' I own. Where one doesn't already exist, it's easy to modify them to fit a different purpose because a 1/10 scale model truck is basically a 1/10 scale model truck. Drill an extra hole here, bolt an extra corner bracket there, that kind of mod. I only have access to a 3D printer through the local public library.
My initial thought is that the servo would be mounted on top with a kind of four-legged bracket or something so that the servo horn is flush flat against the top centre of the joystick, servo horn slightly offset. I would purchase a custom joystick cover (they makes all kinds, skulls, 8 balls to supe up your 'chair) and affix the servo horn to that, so it is never directly fastened to the stock joystick.
I could easily hack into the thing, all I would do is tap the motors directly into a Sabertooth 2x60 and control it that way. However, I will not be doing even that as I want this almost factory new condition chair (the armrest foam has a bit of wear, otherwise it's mint, all documents, foot/headrests/charger, everything). If I remove the boot on the joystick, I still have to manipulate it externally. They are factory calibrated to the control console, I don't want to jeopardize that so the chair is of max value to the MofD once I'm done with it.
I believe the protocol is packetized serial, if you were curious.
I was thinking similar but can't imagine what material, shape/form and orientation the linkage(s) would be. Funny, joystick controlled servo I can whip out in a flash. Servo controlled joystick on the other hand...
