Brushless Gearless Motor for Power Wheelchair

[lhogg1]

I am currently designing a next generation Power Wheelchair using the most up to date technology and materials.
However, I am currently finding it difficult to locate a brushless and gearless direct drive motor for the wheelchair. I have looked at motors such as the Mars brushless PMAC motor ( http://www.robotmarketplace.com/products/ETK-ETEKBL.html ) however this motor would require a gear reduction system which is not what I would like. To keep the wheelchair as maintenance free as possible, it is essential that the motor is gearless. The chair will be operating at 48V, which resulted in the Mars motor having an output of just under 3500 rpm, however I was recently told that the wheelchair motor should be turning at something about 150-250 rpm... which is a LOT slower than the actual motor output, hence the gear reduction needed.

I come here to ask if anybody on this forum knows of any motors that may be of any help to me.

The brushless hub motors that are used in electric bicycles such as ( http://www.elifebike.com/peng/iview.asp?KeyID=dtpic-2011-1G-K59E.3DNJU) offer a similiar rpm that is needed for the wheelchair, however I am not sure how i'd be able to implement them with wide flotation tyres such as these ( http://www.terraintyres.co.uk/user/products/large/Kenda%20Superturf%20K500.jpg ). So if anyone has any innovative ideas in that sense then by all means fire away.

Any help is greatly appreciated and I look forward to reading any replies.

Cheers,
Lewis

 

[amberwolf]

You might look up the powerchair motor thread I started about using an existing powerchair motor (brushless/gearless) for an ebike. Has info about existing such motors already designed for the purpose.

Also, Goldenmotors in China makes motors specifically for powerchairs, that are very similar to the hubmotors we use on ebikes.


Regarding motor RPMs and such, that'll all depend on your final wheel sizes, so you'll need to learn to do calculations about RPM vs road speed vs wheel diameter/circumference, etc., as well as legal limits on powerchair speeds in various jurisdictions and circumstances, assuming you're designing this for eventual sale to the public.

 

[lhogg1]

Thanks for taking the time to reply amberwolf, greatly appreciated.

I have since had a look through your thread where you take the power wheelchair motor and use it on your ebike. Very interesting, and a lot of the stuff talked about is waaaay over my head, especially the stuff about controllers etc. Do you know what makes and models of wheelchair brushless/gearless motors that you used?

Thanks, I've had a look on Golden Motors website and the motors there are nice, although the rpm values are too high for what we are looking for. The problem we have is to reduce the rpm to a more suitable value without the need for a gear reduction system.

Yeah the next step for us will be to calculate the RPM from what stuff we already know about the wheelchair. We already have our wheel size decided so it should not be hard to work that out.

Thanks for your help!

 

[amberwolf]

Remember that the RPM values you see as specs for a motor are simply the "max" for the voltage they are "rated" for. You can get any RPM you want out of a motor simply by using a lower voltage on it (or a lower throttle input to the controller than maximum).

And the RPM values on a hubmotor translate to vehicle speed differently depending on the size of the wheels. The smaller the wheels the slower the vehicle will move for the same RPM of motor, *and* the more torque the wheel will have for the same power input to it. Exactly the same as if you geared the motor down. This is why i use a 20" rear wheel on CrazyBike2 now, so I have better startup torque on that wheel, since I don't need a fast top speed.

That's also one reason why many powerchairs use very small wheels. (ones meant to traverse outdoor terrain tend to have larger ones simply so they can overcome more obstacles than those meant for indoor / household use only).


Unless you can post details of your project then it's unlikely we can help you find specific motors or other parts, though, because we need to know all of your requirements to find matching items.

Knowing what speed you want it to go and the wheelsize, you can figure out what max RPM you want.

Knowing what voltage you'll be running at you can figure out what RPM a motor will actually have based on specs for a motor's RPM at a specific voltage, then using hte previous info you can see what speed that will give you.



All the info I presently have on the motors is in the thread. After my housefire everything is in the backyard or in sheds, until they rebuild the house, so I have no idea where the motor might be now to go check it's label. If there is a pic of the label in the thread then that should have the model, but I don't remember.

That particular motor is meant ot bolt to the frame of the chair and have the tire mount directly to the "rim" tha'ts part of the motor (actually is it's rotor). Other motors use a shaft to mount a wheel to (like the geared brushed motors I previously used on CrazyBike2).


As for controllers, that's a thing you'll have to work out for your particular project, becuase it depends on how your users will need to input their controls. If they can't move their hands and can only do chin controls, for instance, you'll have to work out some method of translating their input into throttle and brake controls for two separate motor controllers, assuming you use the typical one-per-side "tank" style. If you use just one motor (in the wheel that steers, like in a delta trike design), then either your system will have to be even more complex to include a motor to control the steering direction or it will be limited to users that can physically turn the handlebars. It simplifies the traction motor control but it complicates the steering mechanism.

But either way without knowing how you're designing the powerchair we can't help you figure out which controllers or motors might work to do what you want.

And either way you'll still have some work to do translating user control input into something the available controllers can use. There are controllers around for other powerchairs that can do two motors (or more) but you'd have to find out from the dealers for them if you could even buy them as anything but replacements for the original chairs, and if you could buy the special programmers needed for them to set them up for your uses (often a user has to have their chair customized to their capabilities and needs).

The last step is batteries--once you know what the chair has to be capable of, power and range wise, and how fast it has to recharge, and it's weight and size limits (and available volume for batteries), then those can be chosen. They're usually the most expensive part of an EV, either in initial outlay or in ongoing replacement costs, depending on which kind you choose.

 

[athlon]

hello,

up to today I think the best wheelchair for legs disabilities is the zoomcamp
http://www.youtube.com/watch?v=4DD8gNhg9hM

the only problem is that you need fully functional arms to control it so can be useful only if you are young and witout legs.

For older people it can be hard to control and most of the time a differential drive with 2 caster wheel in the back is the best option like the Ottobock B600/B500

one of the biggest improvment is the switcing from the old rear drive configuration

to the new front wheel drive configuration ( the B600 still be compatible with both configuration but for the future front drive is much better)

 

[amberwolf]

FWIW, out of the styles I have ridden, I find the ones with larger center-drive wheels and casters at the four corners easiest to maneuver, if I have to use a joystick or other non-handlebar method to control it, plus it can turn as a pivot around it's own center point, so it works very well indoors or if I have ot turn it around on a sidewalk, narrow path, etc.

However--some of them tip easier when riding sideways on slopes, like when crossing driveways on a sidewalk and hte like, if there's too much weight up high (like if carrying a lot of shopping cargo/bags/etc, since there's no place down low to put anything, really, it kinda has to be hung off the seat or kept in the lap, on the versions I've ridden and the one I own).


I don't really like the 3-wheel delta rear-drive/front-steer types, because you practically have to stop to prevent tipping in a fair number of circumstances, when you want to turn sharply like at a street corner sidewalk, where it often ramps downward to the crosswalk. It does have better cargo/shoppingbag capability, but it is also a handlebar-steer type (at least, the standard ones I've ridden were and the one I had before the fire was).