Do any of you motor experts want to weigh in on this new MGM Chinese motor?

[TheKaiser]

I recently saw this motor in the coverage of the big bike show going on in China. They claim it is entirely a magnetic drive, with no mechanical gears. I would think that wouldn't offer much torque, but they claim 80nm, and they claim it has much lower drag. Do any of you electric motor experts know if this sort of design really has merit for MTB use?

Starunion MGM (Magnetic Gear Motor)

Starunion had their MGM, Magnetic Gear Motor, on display. Not only is the motor super compact, think TQ, but it also promises to be more reliable and need less maintenance as it uses magnetic fields to transfer torque rather than the nylon or metal gearing we see in other motors. The design also...

www.vitalmtb.com

 

[Astro66]

The problem with magnetic couplings is that if you exceed the rated torque, like when climbing in a low gear. The magnetic coupling will decouple and the motor will slip. This will produce a fairly undesirable effect with your pedalling. I can see many grazed shins, let alone it won't produce the most natural cycling feeling.

 

[TheKaiser]

The problem with magnetic couplings is that if you exceed the rated torque, like when climbing in a low gear. The magnetic coupling will decouple and the motor will slip. This will produce a fairly undesirable effect with your pedalling. I can see many grazed shins, let alone it won't produce the most natural cycling feeling.

Thanks for the reply! I think I may have witnessed/experienced the type of behavior you describe with brushless electrical motor devices (including a few throttle operated front hub powered e-bikes) in the past, and I can see how that would be pretty brutal on a technical climb. Quick follow-up question/point of clarification for you, and please forgive my ignorance regarding the various ways an electric motor's architecture can be set up: Don't all of the popular bike motors use magnetic couplings at some point in the drive system? My assumption is that they do to generate the initial motor assist, but then they transfer it through the gear system to adjust the RPMs to the optimal level, whereas this MGM motor sounds like it provides the assist directly, with no gear based translation to adjust RPMs. If so, and if all e-bike systems use magnetic couplings, I can still see the MGM being problematic if the lack of gears is what puts it into the danger zone of decoupling due to excess torque, but I just wanted to confirm if it was magnetic couplings in general that were a problem, or just this application of them.

 

[Astro66]

When you overtorque a brushless DC motor, or even an AC induction motor, you will get slip, but the motor just slows gradually. A motor with a magnetic coupling to the output shaft. When you go past the magnetic couplings torque threshold, and the coupling decouples, the output shaft can completely stop, before you remove the over-torque and the coupling re-engages.

This has been my experience with pumps that have magnetic couplings. Perhaps these people have solved that. You would need to try the motor and over-torque it.

The point of a magnetic coupling really is to prevent damage, when you over-torque the motor. That's why they are used in industry in particular applications.

 

[DirkWisely]

This thing does sound neat, but I don't understand the magic. All electric motors are transmitting the torque via magnetic fields, so there's nothing strange about that. All current e-bike motors find the need to gear up or down (I'm not sure which) using gears.

The problem with magnetic couplings is that if you exceed the rated torque, like when climbing in a low gear. The magnetic coupling will decouple and the motor will slip.

Couldn't the cranks still be attached to the front chainring? No possibility of slip then, and the motor can still apply torque to the crank shaft.

 

[Astro66]

This thing does sound neat, but I don't understand the magic. All electric motors are transmitting the torque via magnetic fields, so there's nothing strange about that. All current e-bike motors find the need to gear up or down (I'm not sure which) using gears.



Couldn't the cranks still be attached to the front chainring? No possibility of slip then, and the motor can still apply torque to the crank shaft.

How do you stop the cranks from continuing to turn in over run, or even as the motor just decelerates, when you stop pedalling ?

 

[GodsTherapist]

Star Union MGM, Another light contender?

https://www.linkedin.com/posts/evak-tian-7016a830b_mgm-magnetic-gear-motor-from-star-union-activity-7213693503250341888-lE1h Seems like alot of focus from the industry on getting to as compact as possible for light weight yet retaining at least a mid level of power this cycle at Eurobike? The...

www.emtbforums.com

 

[TheKaiser]

Star Union MGM, Another light contender?

https://www.linkedin.com/posts/evak-tian-7016a830b_mgm-magnetic-gear-motor-from-star-union-activity-7213693503250341888-lE1h Seems like alot of focus from the industry on getting to as compact as possible for light weight yet retaining at least a mid level of power this cycle at Eurobike? The...

www.emtbforums.com

Thanks, I had not seen that thread...although it leaves more questions than answers...BTW, I love your username!

 

[72dan]

The problem with magnetic couplings is that if you exceed the rated torque, like when climbing in a low gear. The magnetic coupling will decouple and the motor will slip. This will produce a fairly undesirable effect with your pedalling. I can see many grazed shins, let alone it won't produce the most natural cycling feeling.

I have to agree. I sell industrial equipment. We use mag drive pumps for some chemical and sea water applications, they are always low pressure pumps because of that reason, rarely more than 20 psi output if that. I wouldn't buy a mag drive bike motor.

 

[DirkWisely]

How do you stop the cranks from continuing to turn in over run, or even as the motor just decelerates, when you stop pedalling ?

Good point