Rear wheel / hub motor replacement options?

[cornmaze]

That's exactly what I've spent the weekend trying to figure out. I'm trying to find a near-enough substitute that is already in a US warehouse. jkvt in this thread notes that "For what it's worth, I'm in the process of swapping out the display/controller for KT, but I kept the Das Kit motor. Not done, but I did plug things into the motor to see if they worked and they seem to. It responded properly to throttle and read a speed on the speedometer. The KT vendor said it's compatible with Bafang motors so, if KT works with Bafang and Das Kit, then it's probably safe to say Bafang and Das Kit are both compatible with each other (same pin layout). Anyways I know the OP has a solution but figured I'd put this here for anyone else now or down the road." So maybe I just buy a Bafang motor like https://www.aliexpress.com/item/225...d16539372636081475ecb8b!12000026880686191!sea and see where that gets me?

But the other thing I'm wondering about is this: What's wrong with my motor? I know it's the motor: I have two identical bikes, and when I swap the motor out of the casing on one bike an into the other I get the same problem. But I can't find a description of the problem online (namely, that the motor is running weakly, but not otherwise inconsistently or with a power drop or other things I can find described online). When I watch a motor teardown (

) I just don't see that much that can go wrong with one of these things. It's not the internal gears, I can see them clearly and there's no broken teeth or obvious sign of wear. What wiring I can see looks fine. There's no scorching or any loose parts. I'm thinking of getting a gear puller and pulling it apart, but I suppose the question is If one of these motors is broken will that be visible if you dig deeply enough?

 

[EnduroDad]

I agree, there's not much to these motors, very simple design. It's probably quality control at the factory or cheap materials.

Let us know how it goes if you try another manufacturer. I have a feeling it'll work as long as the connector is the same.

 

[cornmaze]

Hi all, a new bit of info here: still without a new motor, I reassembled the wheel to see if there was anything more to be learned. What I found was that when I first power up the motor it offers very little thrust but as the seconds go by it begins to get some grip. As you might know, an ebike under power is very difficult to hold back; due to the damage to the motor my bike is easy to hold in place when I first hit the throttle, but it becomes harder and harder to hold in place as something, internally, begins to catch, transmitting the energy from the motor to the wheel. I think this has to be the planetary gears, and even though they don't show any obvious damage, my next plan is to swap the planetary gears between my two motors and see if that transfers the problem. If so, then I just need to replace the planetary gears. If there's a reason this can't be the planetary gears please let me know and save me the trouble, otherwise next weekend....

 

[cornmaze]

I didn't swap the planetary gears between the two motors because I don't own a gear puller. But, after much measurement to confirm I'm getting the right replacement part, and on the theory that it's the clutch that's part of this assembly, I just ordered a new planetary gear and clutch replacement as well as the gear puller I'll need to install it. Arrives Thursday! Are we nearing the end of this >half year odyssey?

 

[cornmaze]

I received my new planetary gear and clutch and the gear puller to get the old one off. There was no sign of visible damage on the old one; aside from the grease it looked exactly like its replacement, so I suppose I shouldn't have been surprised that replacing it had no effect on my problem. But the exercise was productive, because it was only when I pulled off the old assembly that I realized the metal piece (shown in the photo below was broken.... In the photo, below left, I hold it as a single piece, because I'd glued the top (the part that sticks out of the little u-shaped hole above the central sprocket) to the bottom (the part that goes in that hole). The top and bottom halves of this had sheared off, so I think that's what's prevented power from transferring between the motor and the shaft. I think this is a design flaw: as shown below, there used to be four slots with metal fittings to transfer power between the motor and wheel, and in the new design there's only one. I'm sure it makes it easier to install a gear and clutch assembly, but it also means that if you have an issue with that one slot you're done. Seems doubtful that some superglue will fix the problem but that's what I'm trying because a replacement part doesn't seem to exist.

 

[cornmaze]

It's done! The broken metal "key," shown above, was indeed the problem. I checked with MXUS in China (fast reply!) if they had replacement parts for this, but, after scolding me for trying to repair my motor on my own, they confessed that this wasn't a standard part, just something they made in their own factory for these motors. They were willing to send me one, but it was much faster and more certain to make my own: I cut off the end of an appropriately sized hex wrench, stuck it in, regreased the motor, and am back on the road. Thanks all for the advice. My conclusion from this experience is that if the motor breaks, you just have to pull it out, disassemble it to a reasonable degree, and look at all the bits. Had I started with that this would have been days, not months, to get it up and running again.

 

[Fred]

It's done! The broken metal "key," shown above, was indeed the problem. I checked with MXUS in China (fast reply!) if they had replacement parts for this, but, after scolding me for trying to repair my motor on my own, they confessed that this wasn't a standard part, just something they made in their own factory for these motors. They were willing to send me one, but it was much faster and more certain to make my own: I cut off the end of an appropriately sized hex wrench, stuck it in, regreased the motor, and am back on the road. Thanks all for the advice. My conclusion from this experience is that if the motor breaks, you just have to pull it out, disassemble it to a reasonable degree, and look at all the bits. Had I started with that this would have been days, not months, to get it up and running again.

View attachment 135479

Well done!