Technical Advice/Specs Needed on GM Hub Motors

[engstudent]

Hi all,

I'm an electronic engineering student from South Africa. As part of my final year design thesis, I'm building a self-propelled, bicycle-drawn, electric trailer of mass no greater than 50 kg. The idea is to have two independently driven wheels that respond to force sensors in the tow-hitch. The specification calls for a force magnitude no greater than 1N from the bicycle for full four-quadrant motor operation. My primary focus is the design and construction of the motor drive and feedback control electronics of this trailer.

I’m researching suitable hub motors for this project, and GM seems to have the perfect ones (MW12B, PW16D or equivalent). My problem is the lack of technical documentation for these motors. The performance curves are very useful, but I wish to know information more pertinent to the motor drive/controller. Do the motors have hall-effect position feedback? Are they 3-phase block commutated? Is there any other integrated electronics already present in the hub motor? Are these motors suitable for a standing start, or do they require some rpm before kicking in.

Unfortunately it seems that email communication with GM is hugely tedious (I've yet to get a response from a myriad of emails sent), so I'm resorting to trolling the forums.  

Kind regards,

Engstudent

[Cornelius]

I think all GM's brushless motors are 3-phase with 3 hall sensors for position feedback (giving them standing-start capabilities).
There are no other electronics inside the hub motors, except for the Magic pie motors with internal controller (which are the same as the 'Magic Controller', but integrated inside the hub).

Interesting project you have there.

Since the throttle for the Magic Controller are hall-sensor based, you're not far from being able to use that controller directly...

[engstudent]

Thank you very much Cornelius for your response.

I think all GM's brushless motors are 3-phase with 3 hall sensors for position feedback (giving them standing-start capabilities).

Good stuff! Do you by any chance know the rated voltage and current of these hall sensors? Also, is there any information available on the commutation sequence required to drive these motors?

Interesting project you have there.

Yeah. It's somewhat daunting, but I relish the challenge.   

Since the throttle for the Magic Controller are hall-sensor based, you're not far from being able to use that controller directly...

A controller would be quite convenient, but this project examines my ability to construct one from scratch. I'll probably also have more exact control (not necessarily a good thing  ) over the motors to ensure that the feedback loop performance is optimised.

[engstudent]

I'm interested in the MW12B Motor Wheel. Is there any possibility to access the electrical and mechanical specifications for this motor, eg:

Electrical Specs
-Rated Current
-Peak Current
-Back EMF Constant
-Resistance of each stator winding
-Inductance of each stator winding
-Electrical Time Constant

Mechanical Specs
-Rated Speed
-Stall Torque
-Torque Constant
-Friction Torque
-Rotor Inertia
-Thermal Impedance
-Thermal Time Constant

I realise some of these values can be extrapolated from the performance curves, but having a datasheet to refer to would be fabulous.

[Cornelius]

I do not think there's any datasheet available to the public (if at all?), other than the performance curves...

The only additional information I know of are that the rotor are of the iron core type, and the magnets are Neodymium (NdFeB); which are very powerful and care should be taken when disassembling/assembling the motor (because of the magnetic pull; the forces could be enough to crush fingerbones...), and that the phases are at 120 degrees... I'm not sure about how many poles there are for each phase though.

Oh, and the GM controllers are ofcourse PWM, and the hall sensors inside the motors works at 5V, and delivers 0V to just below 5V out... (You'll be counting/timing the pulses from them though; not variable voltage outputs as in the throttle hall sensor... )

I'm guessing your job would be to find the perfect pwm timings, and values from your hall sensor at the coupling to adjust needed power, etc...

Information such as number of turns, coil wire thickness, phase resistance etc, i'd  guess you would have to find out yourself by disassembling one... I'd guess the motor you're interested in would look very much alike the bicycle hub motors, which there are several inside pictures of somewhere here on the forum.

(I myself have personal experience in building an air-core generator with N45 Neo magnets on 2 rotors; one on each side of the stator. When assembling/disassembling the rotors, one have to use threaded rods to slowly force the rotors together/from each other because of the magnetic pull I've heard of several people loosing fingers because they weren't careful... )
Sorry; rant over...

[engstudent]

Thank you very much Cornelius.

I think I've got enough information to go on. I can probably determine the other motor parameters experimentally.

Your input is greatly appreciated. 

My bravado notwithstanding, it's quite likely that I will return in a couple weeks with more queries...