Friction Powered.... Wheelchair?

[spiffy577]

Hey everyone!

Be prepared for a very noob question... lol. I would like to be able to create a two motor friction drive for a wheelchair (one motor per wheel). One problem, I have not one clue where to start. I need to push 160 or so pounds at 10 MPH or less. I would love at least 5 miles of range and weight is an issue so that helps with battery size / type. Also I would like to attach the motors on the backrest so thinner motors would be better.

So, any advice on what batteries and motors I should use? (See? Noob!) I am quite mechanically inclined but I am just not sure where to start. Oh, and a controller..? Thoughts? Would love a single joystick control but "tank style" could work too?

What do you think?

Thanks!

 

[MadRhino]

Prepare for a spin when one of your motors fail.

 

[spiffy577]

That would be amusing... lol.

 

[amberwolf]

Since the wheels are essentially the same as bicycle wheels as far as a friction drive goes, you could easily use any existing bicycle friction drive system (of which there are many successful ones already developed and tested just here on ES, if you look around for them in their various threads). If you don't want to get one of the ones that's actually manufactured and sold, you could still use the ideas to build one of your own, or at least figure out what NOT to do.

Battery, well, that's up to your budget. You need the same thing a bike does as far as power and whatnot, probably a lot more capacity because of wasted power in steering and stuff.

Control systems...you could turn two regular throttles into a joystick type, with a little electronics in between that and the controllers to convert it into steering. It would be a lot easier to use than tank style. If you have experience in op-amp stuff, you could do it witout programming. Otherwise, an MCU is probably easier, if you can write the programs. If you don't want the complexity of design, just use two throttles as tank style, but it will take some doing to learn to control it.

Another method that might work simply, if all you need is forward motion, is to use two pots. the first would take the full voltage range of the throttle, and vary that from zero to max to give you control over forward speed. The output of that pot would then go to another pot's center tap. That pot's left tap would go to the left wheel's input via a transistor circuit or op aamp that takes the input from the pot and scales it to equal the full throttle range of the controller. The right tap woudl do the same for the right motor.

But that only gives forward motion, to do reverse you'd have to switch the controllers into reverse, and then use that control to set the speed/direction. You could not spin in place with it like a normal wheelchair. (well, you could, but you'd have to manually switch just one controller into reverse).

Control with the above wouldn't be as easy as using a more complex control system would allow.


What would be much easier is if you use brushed motors for whatever drive you build, and go find an old powerchair's controller and joystick, and use that to run your motors. (I have some here I could let go cheap but I have no idea how to hook them up and make them work, so you'd have to reverse-engineer them to figure that out...it's why I have not used them myself!).


There are a number of patents and webpages with info on friction drives for wheelchairs, too.