Selecting a hub motor for a wheelchair

[nanolight]

Hi all,
This is my first topic but I've been reading this forum with great interest for a while. So first of all, thanks all for all the help in this great community!

Here's my project: I'm interested in building a powered wheelchair with two hub motors and haven't found my perfect motor yet. The idea of the Alber e-motion seems great but quite expensive and I don't need the batteries and controller integrated in the wheel. Btw,would anyone know if it is a geared or a direct drive, as the batteries are directly integrated in the center?
I've also read a few hub motor wheelchair topics like this topic and checked out the golden motor PW-12H and it could be ok but it's brushed with quite a low efficiency and I wouldn't be against a dual shaft if that opens more possibilities.

Here would be my requirements: Continuous power between 100 and 200W per motor, max speed around 5mph (that's about 75rpm on a 22" wheel), capability of driving reverse, no oscillation at very low rpm (nice to have)
Would anyone know of an existing hub motor (geared or direct) that could meet these requirements?
If I understand correctly I would need a high pole count, high turn count (low Kv). Is that correct?

I found a few low Kv motors on ebikes.ca or em3ev.com but they are running at higher power/higher rpm, which could be fine if I was just using the low end but I'm sure I won't be in the right efficiency spot.
Is the kv of a geared motor calculated from rotor rpm or from wheel rpm?

Thanks,
Adrian

 

[dogman dan]

Very hard to find a hub motor wound slow enough for what you want to do. 5mph top speed.

You might have to resort to an external motor chain driving the wheel to get the wheel rpm that low with max efficiency.

If you wanted to go faster some of the time, the low rpm motors out there would work, do work well, in 20" wheels. Those are used on the attachments that turn wheelchairs into trikes. the motor in a single front wheel that pulls the chair. You can have a 15 mph top speed, and decent low speed performance on short but steep hills, such as wheelchair ramps. Efficiency will only be poor at low rpm when the load is high. Any hub motor can run fairly efficient at low rpm when the load is not high, such as 200 pounds and flat ground. Go as slow as you like, and as long as the motor turns easy, the low efficiency matters less. the motor won't heat, simply because you are only using 100-200w. But yeah, a higher rpm will be more efficient. It's just that you can just carry 1 ah more of battery to make up for the poor efficiency when the number is that small. And for short hills, like those ramps, it will still get up it fine.

The main thing you should do is simple, make your chair with 20" wheels, and then the existing low rpm dd hubmotors will do you fine. Top speed will be still under 15 mph, so not dangerously fast.

Same concept went into the Liberty Trike, which has become hugely popular with handicapped people that can sit a trike saddle. It uses a low rpm DD hub motor in 16" wheel. It simply kills it on steep wheelchair ramps. Runs efficient enough at low speeds to go an amazing distance on a 400 wh battery. So you see, even not maxing out efficiency, it's way good enough.

FWIW,, all the motors need to sit in a fork. They are NOT like a regular hub on a wheelchair. So it would mean a custom chair, or a big modification to an existing chair.

The cool thing about this idea though, is you can then run one motor forward and the other in reverse. In effect, steer with the motors like a zero turn mower. Only DD hub motors can reverse.

 

[amberwolf]

The main thing you should do is simple, make your chair with 20" wheels, and then the existing low rpm dd hubmotors will do you fine.

Catch with smaller wheels is that they don't climb steps, curbs, etc.--lots of places are not wheelchair accessible, because hardly anyone ever thinks about that sort of thing when designing or building stuff on the ground (or they make one piddly little path for wheelchair traffic, which when blocked by another unthinking person means someone in a chair that can't climb steps/etc is now barred from everything past that point). And anything unpaved can be completely untraversable with wheels that are too small (26"+ and possibly requiring wide tires, too).

Having been in a wheelchair a bit when I broke my ankle, and having worked on several versions of Tiny's Wheelchair Project so she could still get around the yard, house, etc. on her own as she got sicker, I found pretty much that the larger diameter you can make the wheels, the better off you are.


I don't have any particular motor suggestions, though, other than that you could probably take a DD hubmotor that fits all your qualifications other than it's unloaded speed at your voltage, and rewind it to get the speed you're after.

Oh, and you could use geared hubs, but you'd have to lock the clutch in it to get it to be reversible.

 

[Drunkskunk]

A hub motor for a bike is going to be too fast for a wheelchair. it's not the top speed thats the problem, it's the bottom speed. Hub motors aren't designed to go slow very well. You could modify one to have a much higher wind count, but you would still have trouble with the pole count. As each magnet moves past it's pole, you would get fluctuating torque. at very low speeds, in a wheelchair, it might feel like rolling over a small mound every 4 inches or so.

This idea needs a high pole count motor capable of being mounted on only one side. nothing like that exists for an ebike.

 

[nanolight]

Efficiency will only be poor at low rpm when the load is high. Any hub motor can run fairly efficient at low rpm when the load is not high,
The main thing you should do is simple, make your chair with 20" wheels, and then the existing low rpm dd hubmotors will do you fine. Top speed will be still under 15 mph, so not dangerously fast.

That's a good point, the best would be if I could find an efficiency map like this one for the motors I'm interested. But if the speed given by manufacturers is the base speed shown on this map, I would definitely get further away from the high efficiency.

This Mac 500 looks quite good in a 12turn, I wonder if it could be wound with even more turns... It's a 16 pole, I'd be interested to find a higher pole count maybe.
Do anyone know of other websites that summarize available hub motors (besides ebikes.ca and em3ev.com)
Also does anyone know of companies/people that can rewind reliably?

So it would mean a custom chair, or a big modification to an existing chair.
The cool thing about this idea though, is you can then run one motor forward and the other in reverse. In effect, steer with the motors like a zero turn mower. Only DD hub motors can reverse.

Yes it's for a brand new chair design so I'm totally fine with a fork, and I thought existing electric chairs could do 360 turn without "moving". If that's not the case, that's definitely a requirement for my design.

Alternatively, there is this, that looks incredibly cheap for a full kit:
http://cnebikes.en.made-in-china.co...r-Conversion-Kit-Electric-Wheelchair-Kit.html
but I don't see how it could reverse because it looks like it's geared (wider motor). I asked them, will see what they answer.

This idea needs a high pole count motor capable of being mounted on only one side. nothing like that exists for an ebike.

I'll be rebuilding the chassis and I'm looking for a thin wheel+fork assembly. A large diameter, thin, high-pole-count motor with a fork might very well be thinner than a wide geared motor.
Do you know where I could search for a high pole count direct drive?

Thanks a lot!
Adrian

 

[dogman dan]

Well, there you go,, that kit looks better for your needs than any bike motor kit would be. I bet those are a slower wind than typical for a bike. And they need no fork. Ideal all the way around. I think it will reverse, even though it's a geared motor. since not a bike, it won't need or want an internal freewheel.

Let me clarify about using a small wheel. I never said you'd ride up steps, or other fu--ed up places that are not accessible. But a bike hub motor in 20" wheel, and 750w of power, will easily climb an 18% grade wheelchair ramp. Two would climb even steeper. Not efficient for those few feet of course, but plenty efficient enough on the flat, even at low speeds.

 

[samsquatch]

Hey gang. Yes, I'm resurrecting an old thread and I apologize in advance for that, but here we are.

I have another thread going on in the General Discussion forum RE low speed, high torque hub or gearmotors:
https://endless-sphere.com/forums/viewtopic.php?f=3&t=96070
My application is to haul a load between the two wheels while using the wheels as a level fulcrum. Anyway, I'm just posting here in case it sends a notification to the OP: what motors did you end up going with for your project?
Cheers
SAM