Axle spun inside dropout, Hall cable broken?

Unfortunately today the axle of my MXUS v3 3T spun inside the dropout.

So I guess torque arms are a must at this amount of torque even for an overbuilt steel frame.

After that happened, the motor stopped working and told me "Hall error".
What do you think most probably happened? A hall sensor cable that broke away while the axle spun?

If the axle spins out, it often twists the wires up ripping the insulation apart on multiple wires, allowing them to short together. When this happens between a phase wire and a hall, it can destroy not only the hall sensor in the motor (easily replaced), but also the hall input on the controller itself (which isn't fixable; requires a new controller).

I'd recommend opening the motor, then pulling the wire *in* thru the axle slot, until you are past the damaged area. THen cut that damaged end off, and rewire from the undamaged part to the different spots the wires went to before.

Then at least you know all the wires are intact.

After that, you can test the hall sensors themselves, via the info at http://ebikes.ca in the Learn - Troubleshooting tab.

If they're ok, then retest the controller with the motor. If it still doesn't work, the controller is probably fried.





These MXUS 450x's can be quite high torque motors, if supplied with enough phase current. If you're also using regen, it rocks the axle back and forth and that's much harder on the axle and dropout / torque arm than just forward acceleration.

A very tight fitting and securely mounted torque arm on *each side* is pretty much necessary for these.

But if you push them hard enough, even that isn't enough:

At least you didn't break the axle yet.

I've done that to two different MXUS, a 4504 and a 4503; the latest:
https://endless-sphere.com/forums/viewtopic.php?f=2&t=67833&p=1404238#p1402078


My torque arms (actually clamping dropouts) held on fine, but the axle coudln't handle all the forces.

Are you listening, hokey Chinese hub makers? Your crap doesn't work. Please fix it. Heinzmann showed you the way well before y'all got into the business.

I tried the second set of Hall sensors and this seems to be fine. At least the wheel is spinning when I turn the throttle.
The insulation where the cable is coming out of the axle is clearly damaged.

However I have another problem now. The thread was damaged and I cannot put the nut back on now (without causing further damage to the thread)

That's easy, if you ahve enough axle length--use washers to space the nut away past the damaged threads, toward the end of the axle.

Unfortunately I cannot even put it on the axle any more probably because the nut damaged the thread when I removed the nut after that incident.

Then I'd recommend checking your local hardware stores to see if they carry tooling called "dies". These can rethread the axle, and then you can use a new nut. You might have to use the next size down, but in SAE rather than Metric.

I forget if the axle is 14mm diameter, or 13mm, but the next down SAE size is very very close to that--just enough smaller that the die would cut new threads into the axle deeply enough to let the new nut securely hold it on.

You could just use the die for the same size as the axle already is, but since it's just clearing the existing threads, and not "fixing" the tops of them, a new nut of the same size won't quite have the same holding power it would have before, or as much as redoing it just slightly smaller would.


You can also build clamping dropouts, also called pinch or pinching; there's various methods posted around the forum, some of which are in the Torque Arm Picture Thread.

Depending on the design, you may not have any need for the nut. I don't use a nut on the inboard axles on my SB Cruiser trike, because the clamps I made enclose the entire lenght of the axle. However, the outer ends of my axle aren't clamped like that, which allowed that end to rock back and forth, and these forces eventually broke the inboard axle off--that's what happened on both of them, and on one other motor.

So if you make clamping/pinching dropouts, do it on BOTH sides.

Otherwise you may have to weld a new end onto the axle like I do. :/

Thanks a lot for your advice!

What about replacing the axle? I could get a new Mxus 3k v3 axle for $30.
Is it a lot of effort to replace the axle and are special tools required?

Some time back an ES member came up with a strategy that uses an M14-to-M20 thread insert and M20 nut that can be used to address damaged threads. If you can clean up the threads enough to screw on the insert just once, the large nut can be used moving forward for normal service wheel removal. You can likely dress the threads with a triangle or other small sharp edged file enough to get the insert in place.

If things are so chewed up the insert is super loose, you might cut off the end of the shaft so it was 1/8" below the the face of the insert and have a TIG shop plug weld the insert onto the end of the shaft (basically place the weld in the depressed area at the end of the insert filling it up). If you go the welding route, I'd back two or three nuts together on the the shaft on the opposite side for them to have a spot to clamp the welder GND without some small arcing messing up those threads...

Check it out here: BMC Hub Motor - customer support - stripped threads

Also with part numbers: https://endless-sphere.com/forums/viewtopic.php?f=2&t=43287&start=25#p651193

hias9 said:

What about replacing the axle? I could get a new Mxus 3k v3 axle for $30.
Is it a lot of effort to replace the axle and are special tools required?

Click to expand...

If the procedure Teklektik outlines won't work for you for some reason (it's much simpler than replacing the axle), then you can look up the various threads about replacing axles in different motors, but basically you have to have (or make) a press with sufficient force to push the old one out and the new one in, and you have to support the stator frame around the axle itself in both operations so it is only pushing the axle, and not stressing the "spider" that connects the axle to the stator. (or you'll break that out and have a much bigger repair job).

(this is the main reason I am attempting to repair my axle in the way I am, rather than replace it)


However...many, if not most, of these hubmotor axles are kinda crappy, so if you're going to replace the axle, I'd recommend either modifying the new one to use something like the Heinzmann torque arm solution, inboard of the dropouts, or having a machine shop make you one that does that, out of *good* quality material, like bicycle axles or good quality bolts would normally be made from. (I have my doubts about the materials and methods used to make most hubmotor axles).

I rarely even install the axle nuts on my motors. Good clamping dropouts make axle nuts just decoration.