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Ash Small

Sat Apr 25 2015, 10:16AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Does anyone have any experience with this type of motor?

I'm assuming the three wires 5a, 5B and 5C go to the motor, which I assume is 3 phase and that the other five wires are to do with position sensing. (I'm just guessing here, though) I understand, from what I've read elsewhere, that when just using one, you don't need to use the position sensors unless you want fine control at low speeds, which will be required for my intended application.

I want to fit two of these to a wheelchair fitted with 26 inch mountain bike wheels/tyres, and assume I can control them using PWM and 'H' bridges or similar (I'm assuming a separate IC for each wheel, both driven from a PWM IC, or some similar arrangement, and then implement some form of controlled pulse skipping for steering, one pulse skipping circuit for each H bridge IC)

These are rated at 36V, 250W but I won't want to run them at anywhere near this power (total 500W (2/3Hp) at 7A). Legally, in this country, it can only do 4MPH unless registered for the road.

I am seeking more info from the supplier, but they take a while to reply, and don't seem to know a great deal about their products, apart from general dimensions, etc.

Any assistance will be greatly appreciated.

Bjørn

Sat Apr 25 2015, 10:47AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Make sure you get curves of torque and efficiency because they can be quite bad at low RPM. So it is possible that you need a different type of motor or smaller wheels to get good performance at low speeds.

This site has some datasheets that you can use to get an idea http://www.goldenmotor.com/

hen918

Sat Apr 25 2015, 12:01PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

Sorry Ash, these hubs are designed to be peddled up to ~10MPH before power is applied, they have next to no torque at speeds of a few MPH, and are essentially very high geared, for efficiency at ~15MPH.

Ash Small

Sat Apr 25 2015, 01:38PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

OK, So even if I got two of the 1000W versions, it would still not have enough torque to get moving?

They did suggest a geared brushed motor, but I thought brushless would be more efficient. I don't really want to use drive chains. I think they are designed to be used with the bike's original gears anyway.

I had thought of epoxying neodymuinm magnets alternately north south facing all around the inside of the rims, and then mounting a few chunky coils in close proximity. I'd need ~300 1/2 inch neodymiums to completely cover both inside rims, though.

I'd still need to sense wheel/magnet position to apply the correct Pulses to the coils, though.

Maybe I should experiment building my own brushless hub motors?

I've read the threads on brushless pancake motors and I know that larger diameter brushless motors have more torque.

I did realise I'd need large currents to get the thing to move from stationary, but then I could use PWM to reduce averave current.

Any other thoughts?

Sulaiman

Sat Apr 25 2015, 01:47PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

just imagine how much iron/steel crap your magnets around the rim would pick up,
stuff that would probably jam between coil and magnet assemblies !

you would also have to fix the magnets really well due to shock and vibration
and the wheels would have significant gyroscopic effect and inertia.

Ash Small

Sat Apr 25 2015, 02:41PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Thanks for pointing out these points. I do appreciate it.

Found this online:

Looks like three sensors and quite a few coils, plus some neodymiums. As Sulaiman points out, sticking them to the rim probably isn't a good idea, They'd need to be mounted in a smaller diameter enclosure on the inside face of the wheel.

Thomas W

Sat Apr 25 2015, 06:39PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

I bet Â£20 that the 3 wires on their own are the 3 phases, U V W
and the other 5 wires are hall sensors, +5V, U, V, W, 0V

Ash Small

Sat Apr 25 2015, 08:12PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Thomas W wrote ...

I bet Â£20 that the 3 wires on their own are the 3 phases, U V W
and the other 5 wires are hall sensors, +5V, U, V, W, 0V

Yep, that's pretty much what I assumed.

I will wait and see what the supplier's tech people say regarding torque, and I'm still considering building my own from neo's and coils, in some kind of enclusure about two thirds of the wheel diameter, Maybe 18" dia.), but I'm also considering using a smaller, geared motor, which I don't think will be as reliable as some form of brushless motor. Chain drive will take up less room than a belt, but the other option is direct friction drive onto the tyre. I think some tyres still have the 'friction sidewall' that we used to use to drive 6V dynamos for lighting, back in the day, but whether I can get some for 26" mountain bike tyres, I don't know.

I'd still prefer to use brushless with no gearing if I can get the torque and efficiency I need.

...

Sat Apr 25 2015, 08:41PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

You are correct, the small wires are hall sensors (red= +5v in, black = 0v, yellow/green/blue are u v and w) and the main phase wires are the larger wires (same thing u v w). Since it is a BLDC motor the halls are needed to provide torque at low RPM, so make sure to build/buy a controller which supports sensored operation. The '1000w' 48v motor I have is good for about 80a peak (more like 30-50 amps average) into the windings, which corresponds to about 50 nm of torque. plenty to get a wheelchair moving. A normal '1000w' is geared for about 35mph at 50v in, so for wheelchair applications you can probably get away with a 24v system (good for 12mph or so). If that is even not enough, you can get the '5000w' ones which are good for 150nm a piece. It is worth keeping in mid though, that fundamentally using a direct drive motor for an application where you want the wheel turning at <100RPM is going to be inefficient in terms of weight and cost since motor good for 100w at 100rpm is also good for 1kw at 1000rpm and 10kw at 10krpm (assuming that the bearings don't explode).

Also, I personally strongly suggest that you buy controllers for them off ebay as well (they are incredibly cheap, something like $30 for a 50a/50v controller). They are quite easy to interface to, you plug the motor in, plug the battery in, and put 0-5v into the throttle to get 0-50amps out (yes they are current mode controllers, not voltage mode like a RC style controller). Almost like they were designed for this application

The Infamous Charles has a lot of info on these types of motor controllers

BigBad

Sat Apr 25 2015, 10:43PM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600

hen918 wrote ...

Sorry Ash, these hubs are designed to be peddled up to ~10MPH before power is applied, they have next to no torque at speeds of a few MPH, and are essentially very high geared, for efficiency at ~15MPH.

Don't understand.

How do you design an electric motor with low torque at zero speed and high torque at high speed???

The only way I could see that is if the drive circuitry throttles it.

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