[GlynD]

Hi all,

I'm building my daughter a six-wheel-drive mountain climbing wheelchair which will have 20" wheels with 1500w 48v hub motors (the type you see on E-Bikes and the like). These motors aren't intended to spin at the low speed I'm after and I've been advised that one way to prevent them from overheating at this low speed is to run them at a lower voltage than they're rated for and find a controller that is capable of supplying high currents at say 12v. Controllers for large scale radio control cars spring to mind.

One ESC that's caught my attention is the 200amp Turnigy Trackstar which has a burst current of 1,000a and will take 4-8 LiPos.

Before I go ahead and make a purchase though, I wondered if anybody could advise if this ESC is suitable for my needs?

One thing in particular that I'd like some clarification on is the 4-8 LiPos - I plan on using LiFePo4 cells, is this OK? Let's say each cell had 3.2v. To make up 12v I'd need to use 4 cells wired in series. One group of 4 cells isn't going to supply current long enough to do what I want to achieve so I'd need several groups of 4 cells, with all groups wired in parallel to still give me 12v but with increased amp hours. Is it OK to do this with an RC controller? The reason I ask is that I believe some RC controllers auto-detect how many cells are connected.

 

[madderscience]

knowing nothing about wheelchairs, some thoughts:

six 1500w rated motors means 9000w or about a 12hp wheelchair. I realize that you are looking at substantially overrating the motors because of the low speed, but this seems like humongous overkill. Balancing the throttle control across all of them might be a challenge too.

How will braking work? With that design if the rider turns off power (to stop or whatever, nothing will prevent the chair from rolling back/forward. I imagine "normal" power chairs probably have some kind of automatic brake to prevent that problem.

How will steering work? skid steering (like a tank) probably isn't going to play well with bicycle wheels on rough terrain, even heavily built ones.

Hub motors for bikes typically come with their own matched controllers. I don't know if speed limiting can be programmed in or not but would probably be a required feature.

on component selection, your best battery might be a 7 or 14 stack of nissan leaf modules (about 49-50V) depending on whether 60ah or 120ah is needed and the size/weight of the chair. Well regarded manufacturer LiFePO4 would certainly work too. You won't be stressing the cells insofar as amp draw as long as they are 20ah or bigger. I'd stay away from hobby grade batteries just due to reliability and safety, unless this chair will never be operated alone.

I'm guessing you can get some pretty powerful gear motors off of power chairs designed for adult/overweight individuals. A four wheeled chair with one of these on each corner and some kind of 4 wheel steering system would probably work well. You could uprate the wheels with lightweight trailer tires 8" or 12" wheel depending on clearance needed) or ATV or small motorcycle wheels; what you pick would depend on how extreme of terrain you are really considering. It might require making custom hubs but I bet you could come up with something. Suspension need would be minimal but some amount of articulation would be necessary, low pressure tires could do the rest.

In fact, could you start with a 4wd ATV and modify it appropriately to build a chair? Drive each axle independently with a motor, or keep the central gearbox and drive that? I guess the issue would be seating position, dictating how much of the original vehicle could be kept. I bet the front and rear axles could be used more or less as is.