Powerchair Direct Drive Brushless Motor (High-Torque)

amberwolf

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A friend dropped by tonight with an interesting motor.
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It is from a powerchair, and the wheel bolts directly to it. Normally it would run at less than 200RPM, on 24V SLA, for a few MPH on a small-diameter wheel, but the manufacturers have apparently tested it up to 65MPH on the same size wheel, something over a thousand RPM, which would take a couple hundred volts or so. I don't know if that was bench testing or on-road.
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Being a powerchair motor, it is intended to run for long periods at max output, climbing hills/ramps, etc. Basically the batteries would give out long before the motor would be in danger.
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So it should work for ebike use, too, like I used to do with the powerchair brushed motor/gearbox unit on CrazyBike2's original on-road drivetrain, running it's output thru the gears along with the pedals.
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The catch? It's almost 30lbs! About 7lbs can be removed with the parking-brake assembly, which I would not need on a bike. The rear cover, that basically just protects that brake assembly, could be left off. A bit more might be machined off around the former wheel-hub, on it's outside and it's face, but that's all aluminum so it wouldn't be much weight. Most of the remaining weight is in the copper and laminations of the stator, and the magnets and flux ring of the rotor (inside the hub). Cant' ake anyo of that out.
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So it will still weigh about what a hefty hubmotor and wheel would weigh, and I don't know what kind of performance to expect. I still would like to try it out, though. :) Would be interesting to see how it performs with a good gearing-up to at least 20MPH (just running it on the higher voltage packs I have nearly should do that), then run thru the NuVinci.
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There is a challenge, however: It does not have a direct hall sensor connection. Instead, it apparently has an electronics board that outputs a sin and cosine function of the halls, based on this pinout sheet:
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Neither of us is sure what the EEPROM data and clock lines are for--they may be to reprogram the hall board for specific uses of the motor, or perhaps they read out serially certain data from it, but we don't know what that data might be.

There's no way to physically access the halls directly, either, without removing the rotor (hub) from the stator. These are some VERY strong magnets, and it is going to take a fixture built for the purpose to pull them apart without risk of damaging either fingers or motor, so if a relatively simple (analog electronics) way can be found to use the SIN and COS signals to recreate three separate hall signals for a typical ebike controller, that would be great. I havent' thought of one yet, but I am not really good with coming up with stuff like that.

So anyone else that has an idea, I'd like to hear it. :)
 
Temporarily changed thread title to reflect the question/problem in the first post, and replying here to unbury the question from my usual overly-long posts:
amberwolf said:
There is a challenge, however: It does not have a direct hall sensor connection. Instead, it apparently has an electronics board that outputs a sin and cosine function of the halls,
So I'm looking for a relatively simple (analog electronics) way to use the SIN and COS signals to recreate three separate hall signals for a typical ebike controller. If that's even possible. :?
 
Amber before you go too far, put 5V and Gnd on the pins and scope the Sin and Cos simultaneously while spinning the motor and make sure you get the functions out in analog. What is neat if this is true Sin and Cos is that one could build and advance function pretty easily... easily being a pejorative of course! If you get Sin and Cos the next question is to figure out how they are doing it so cheaply and reliably.
 
I'll have to dig the scope out and see, but I'm pretty sure they actually are analog.

There are hall sensor units out there that are made specifically to output the SIN/COS like this, so that's probably what they are using. Unless I build a very sturdy custom fixture to remove the rotor from the stator, I can't actually check, though. :lol:

I have a pretty good idea how to make that fixture, but I'd rather invest the time in converting the SIN/COS to a signal a regular ebike controller can use. (despite how badly I want to see the guts of this motor ;))


I found that theymake these sensors because I did a quick google looking for any non-math info about SIN/COS hall sensor stuff, like maybe someone else that had already done this for a robotics project, but I found nothing I could understand or use. I did find with "SIN/COS Hall" a list of various things including this:

http://www.motioncontrol.com/articles/ic-mha-magnetic-hall-encoder-sincos-outputs
http://www.ichaus.de/MHA_factsheet_en

There are probably others out there but I didn't go farther, as I don't need that--I need something that turns SIN/COS into three-hall output (which probably doesn't exist and/or ins't possible)
 
Is it possible to put Halls in this motor? If so, perhaps an easier solution?
 
Gordo said:
Is it possible to put Halls in this motor? If so, perhaps an easier solution?
Would be easier, and I'd've already done it, except:
Amberwolf said:
There's no way to physically access the halls directly, either, without removing the rotor (hub) from the stator. These are some VERY strong magnets, and it is going to take a fixture built for the purpose to pull them apart without risk of damaging either fingers or motor,

amberwolf said:
Unless I build a very sturdy custom fixture to remove the rotor from the stator, I can't actually check, though. :lol:

I have a pretty good idea how to make that fixture, but I'd rather invest the time in converting the SIN/COS to a signal a regular ebike controller can use. (despite how badly I want to see the guts of this motor ;))

both I and my friend tried, together, to pull it off of there but we could not get it even 1/4" up off the rotor, because of the magnet strength. The usual way, using consecutively larger prybars and blocks, isn't going to work for this one. Plus, evne if it did, I couldn't safely put it back together afterward, not by hand.

It will require bolting the backplate down to a workbench, very securely, then building a standing fixture over the top of it that will have enough space between it's top and the top of the stator to allow sliding the entire rotor and fixture off of it once it's removed. The fixture's face will have to have bolts threaded thru it that run down into the wheel mounting-bolt holes on the outer circumference of the face of the rotor. Then a single massive bolt/rod can be threaded thru the center of the fixture, down into the extraction hole this motor has in it for this purpose (it's even dimpled already!), and turned until it lifts the rotor off the stator.


A 3-jaw puller could also work, but I don't have one with large enough jaws, and that also won't keep the two parts aligned well enough for reinstallation at the end without risk to magnets or stator laminations/windings/etc. One slip and BANG it'd be all over. :(
 
That's what I'm hoping to avoid. :lol: I already have one broken hand that hasn't healed right (or at all; not sure), so I'd really like to avoid anything worse, like completely removing fingertips and the like. :roll:
 
How about just using a sensorless controller, or is that too easy?
I was ok at math at school, but trig was a headache. Haven't needed to know it for anything since.
 
That would also work, but I'd first have to have a sensorless controller capable of the kind of startup amps this thing is likely to pull (LOTS...I'd guess a spike of hundreds at the startup, under load).

ATM I don't have *any* sensorless controllers that I know of (at least, not working). I have a little board made for converting a sensored controller to sensorless, that run on something like 15VDC (so needs a separate power supply from the rest of the system, as the controller won't provide this; coudl probably run off my lighting pack), but I've never tested it.

Plus, as sensorless, it would probably not startup from a complete stop correctly each time, and I basically can't start out pedalling the bike without the motor helping me to push; my knees would be killing me after only a few minutes of riding (the piont of the motor is to keep that from happening).

If all else fails, and I cannot get the motor apart to put halls in or access existing ones directly, I'll have to go the sensorless route...but I'd much rather have some kind of position sensors in there, tied to the controller. :)
 
In principle, this wouldn't be a very hard thing to do. This is how resolvers output angle, so it's a pretty common problem and there's a lot of info on how to convert sin/cos into angle. The problem is I can't think of an easy way to implement it in analog, all the methods I'm aware of require at least one trig function. It would be almost trivial to do using a simple little PIC or AVR, but probably pretty complex with analog unless you can find a chip designed for the task somewhere.
 
amberwolf said:
A 3-jaw puller could also work, but I don't have one with large enough jaws, and that also won't keep the two parts aligned well enough for reinstallation at the end without risk to magnets or stator laminations/windings/etc. One slip and BANG it'd be all over. :(

Someone, pointed out to me the other day, when using a 3 jaw puller to make sure to tighten all the jaw bolts as tight as possible. This keeps the stator lined up better and reduces the chance of a shark bite.
To assemble, I set the stator of my 3500W motor on two 2 x 4's and then two more on top of the stator. I lowered the wheel on to the shaft, let it sit on the top 2 x 4's and then set up the puller. Once I had tension on the shaft, I pulled out the upper 2 x 4's an used the puller to lower the wheel onto the shaft. Very gentle assembly, with no fuss. I think you can make a puller with just 2 thicknesses of 3/4 plywood and some threaded rods?
 
I finally had a chance to give this another go, and I didnt' need to build a fixture after all. :)
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Turns out it was as easy as pulling the covers of a hubmotor, almost: Pry up a little (millimeter or less at a time) and insert shims until I could stack washers in there, then nuts, then bigger things, at equally-spaced points around the edge, until it was high enough to be able to put my feet on two opposing corners of the base, and grasp the edges of the "rim" on the hub, then pull straight up in one smooth but very difficult motion and it came off.
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The very hardest part was the first centimeter or so, because of friction with the actual hub/axle it is normally bolted to inside the motor. After that, it was a lot easier, so the magnets werent' quite as strong as I had feared.

Putting it back on might be interesting :roll: but it is at least off for the moment, allowing internal access.

Nice long magnets, very wide stator. I expect that means there are less end-turn losses, because there is less end length vs width parallel to the magnets?
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I already know it's cabable of a lot of torque even at low voltages, as it's designed to run on 24V, along with another separately-controlled motor, to haul a large person (potentially 3-400lbs or more, plus the powerchair's weight) around. That means lots of stops and starts, sometimes running for up to several miles at a time, able to do some pretty severe inclines (whatever the chair can do without tipping over), etc.


It does not use three halls. It has a pair of them, probably Honeywell SS495A, if I am reading them right.
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View attachment 1

on an electronics board that I can't quite read most of the markings on. I cannot read the ones on the chip; they're too small and faint (but they are there, if I can get sufficient magnification and lighting).
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These are detecting fields on a small magnetic encoder ring within the hub/axle's end. Dunno how the fields are setup on the magnet ring. (which is the gray plasticky looking ring just on the inside of the aluminum hub I"m holding in hand)
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Really glad I was given the circlip tool a few years ago; it has been invaluable in situations like this:
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So to use this with an ebike controller, I'll have to install halls in the stator. Hopefully I can install them in an equivalent spacing to that of one of my hubmotors, based on number of stator teeth vs diameter, or something like that. I have no idea how this motor is wound (phase pattern) other than that it is done as Terminated Wye. Thick winding, though. :) Phase ends are circled in green, terminations in red.
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Now to find a bit of time to locate some hall sensors that still work, in some other object I don't need, like an old floppy drive or laser-printer mirror-scanner board, salvage them, and start playing with phase/hall combos and hall positions on this motor, to see if I can get it to run on an ebike controller.

If I can, then I can also use this motor to power a super-hauler of a cargo bike, able to easily pull extremely heavy loads. Or, perhaps, a bike that can pull off-the-line really hard and get to speed very fast. :) (assuming I can set up a battery pack that can supply the necessary current, and modify a controller to handle that).
 
If I remember correctly,

x * sin(a) + y * sin(b) = z * sin(c) where c is at a different phase angle.

Which means that by adding scaled versions of two sine waves you can create a third one at a different phase angle.

By doing this three times you should be able to create sine waves with zero crossings where the hall signals have zero crossings, and square them up to be hall signals, so z is not important.

The x and y coefficients can be adjustable pots.

Probably easier to add hall sensors.

Note that hall sensors don't need to be inside the motor, they can be mounted externally if the leakage field is sufficient.
 
Thanks for the formulas...they might help if I get enough time to figure out how to implement those in op-amps, like I wanted to. :)

It is probably easier to add the halls, now that I can see inside the motor to know that they are nto already present (which I was hoping for, but didnt' expect).

I'd already considered just adding external halls down by the gap between motor mounting plate and rotor, but I had hoped they were already inside and just nto directly accessible. I think that just to prevent heat damage to them, I probably will end up doing exactly that. Perhaps on a little moutning board for testing, and possibly embedding them into the aluminum mounting plate for better sensing, once I find the best positions for them.


Right now I am still working on other projects around the house, and resting between, but hopefully will be able to remember where some of my hall-sensor-source-objects might be located, and dig some out in the next few days. I would really like to at least spin up this motor. :)
 
Thanks for opening her up Amber. Looks like 2 linear halls, and they have a multipole ring magnet spinning by them. Might be interesting to figure out how many poles on that ring magnet, you might be able to place digital hall sensors and use that ring magnet to trip them.
 
That's a thought...but given where that ring is inside, I'd have to "know" where to place the sensors, because putting them in there means reopening the motor for every adjustment to their position. ;)

I'd much rather play with positioning them on the outside, if possible. Failing that, just physically putting them in a 120 degree physical arrangement on the stator itself.


If I did want to determine the spacing and polarity of the poles on the ring, what would I do? Wire up a single hall to resistor and LED, and rotate the ring past it to watch it toggle on and off?
 
Your idea is pretty much what people used on cars with mechanical distributors: a timing light.
 
Is there a name or identifying model numbers on that motor ? Looks like a good candidate for the hills here.
 
Thanks for that info. I was all over Invacare site, BG searches, and the info for making these things run. Just could not find a picture to be sure of what I was reading. There was another named company that controls the info, and, makes it difficult to
obtain. Can't remember the 3rd company name.
Anyhow, They sense off of 2 sensors, and, the controller makes up the third sensor info, or not, depending on the application.
 
I found an old floppy drive that has halls for motor position sensing. Gotta get it apart enough to get them out without damaging them, and see if they'll work for this. :)
 
Haven't had time to get the drive apart yet, but Icecube57 had lowered a pre-wired/pigtailed hall set to $6 (from $12),
http://www.endless-sphere.com/forums/viewtopic.php?f=31&t=33602
so in the interest of time saving plus having a known-good set of halls that I know should work for this purpose, I bought them, and they will probably be here in a little while. LIkely before I will have time to get back to this project, anyway.


I also changed the thread title back to "Powerchair Direct Drive Brushless Motor (High-Torque)" from the "Use SIN/COS position sensor output to recreate 3hall signals", since it's unlikely I will be able to accomplish the latter anytime soon. (though I would still like to find a way to do that, just because it would make it easy to use off-the-shelf motors that sense using SIN/COS on our ebike controllers, with no modification of the motor at all).
 
I finally remembered to measure things:
Stator: 50mm width, 170mm diameter
Magnets: 53mm width, 171mm diameter (0.5mm airgap at most)
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Got a donated Lyen 12FET sensorless controller that probably has a bad drive transistor. If I can fix it, I can test this motor with it.
http://endless-sphere.com/forums/viewtopic.php?p=493399#p493399
file.php
 
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