Does my brand new hub motor (Aikema AKM-128CST) have a bent axle? (4K video)

Comrade

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So I made a really sturdy bench motor mount out of a 2x4 clamped to the workbench, and plywood sides that are glued down and screwed down. And I noticed that there is a very visible wobble that it seems the axle is introducing.

I have never owned bike motors before, but this does not seem like an acceptable manufacturing tolerance. :shock:

Will my dropouts break off with this thing? :lol:

[youtube]iApMtaHPlCE[/youtube]
 
A bent axle won't cause that kind of cyclical movement, because the axle isn't turning. What you have is a motor housing whose bearing seats aren't along the same axis.

Working back and forth like that is likely to break your axle and/or your dropout welds eventually.
 
Chalo said:
Working back and forth like that is likely to break your axle and/or your dropout welds eventually.

So +1 vote from you that this is completely unacceptable and should not have passed QC? :mrgreen:
 
Comrade said:
Chalo said:
Working back and forth like that is likely to break your axle and/or your dropout welds eventually.

So +1 vote from you that this is completely unacceptable and should not have passed QC? :mrgreen:

I wouldn't use it. What recourse you have with the seller is an open question, but I think you're inviting problems if you ride it the way it is.
 
Chalo said:
What recourse you have with the seller is an open question

I have the power of $300B+ Mastercard Inc. on my side. :lol:

If I get a new motor, what tolerances would be acceptable? Visibly no wobble at the minimum?

I bought cheap Chinese things plenty time before, but have no baseline of what to expect with $150 hub motors.
 
Comrade said:
If I get a new motor, what tolerances would be acceptable? Visibly no wobble at the minimum?

If you can't see it wobble, it's probably fine. I would not expect better from the QA that its low purchase price can provide.
 
Is there a good mechanical drawing of the internals of a typical geared hub motor available somewhere?

Still trying to wrap my mind where the defect in the motor might be.
 
Comrade said:
Still trying to wrap my mind where the defect in the motor might be.

Wish the video was more zoomed out. Trying to think what would cause it to wobble side to side like that. You could try changing the bearings but it’s likely something else. Did you show the seller the video?
 
Eastwood said:
Trying to think what would cause it to wobble side to side like that.

Without 3D video, zooming in would not help showing how it wobbles. It's actually as if the axle is moving in a circular motion. The axle is fixed in space at the nut position, but is moving in a circle in space where it enters the motor body.

I'm not 100% certain what the insides look like, but if the axle is a 2 piece, one side might be press fit into something at an angle.
 
Eastwood said:
Trying to think what would cause it to wobble side to side like that.

One or both of the bearings is pointing in a different direction than straight along the axle. That's really all it can be. We don't know why yet.
 
Bearings would be a solid first place to look and they are easy and cheap to replace, I had to replace one years ago. I went back to the same transmission place I bought the bearing for the cover plate now for the Cyclone mid drive bottom bracket and quoted $18 each (just needed two) the bearing for the cover plate was $9-12 but can be had on ebay for cheaper if you find the lettering. The transmission shop was very helpful as he guided me through a little snag which was that there were 2 stock numbers for 2 bearings with the same markings but one was wider then the other, I ended up passing on purchasing the bearing, and never built the mid drive. It ended up that the bb axle was not the problem, sure it was crusty and rusty but some sanding and oiling was back to being good.

A few other things you can check is to be sure that the cover plates are bolted all the way in, before you do anything scratch a mark on the cover plate and motor so it goes on the same way as you take it off. Be good to take a closer look at the inside and the cover plate bearings.

Its not like cheap motors have great quality control assurances or their tolerances arent really precise nor should they be for bicycle stuff and its not like they really care as long as they get their money and the product is shipped.
 
[youtube]yRbe4_CVrto[/youtube]

I mounted the motor in a junk steel frame, to see what happens, and the motor has no problem bending the dropout back and forth. :(

That's no good for sure.

And here is the response from the seller.

Hi Dear,

Just check it with our engineer and AKM, they all said it is normal.
Because you did not install the rim, the shaking will be more obvious.
After you finish installing the rim and installing the bicycle, the shaking will not be so obvious.
Thanks.

I guess at this point it would be fair to say that the seller is Top Bike Kit (topbikekit.com) and they have no problem if a customer destroys their expensive bike frame with a defective motor. They are even encouraging me to do so. :lol:

But that unfortunately seems like the norm with Chinese businesses. Not interested in keeping a reputation. Not interested in repeat customers. :roll:
 
At this point we can see it’s not safe and will probably snap the dropouts at some point. So this being the case just open the motor and change the bearings, reassemble and see if it fixes it. You have nothing else to lose, doesn’t sound like the seller wants to help. My last two hub motors I had to change the bearings. I believe they were defective from the factory as they never rolled smoothly even before the hub motors were laced in a rim. Since these hub motors are cheap products from China they smack cheap bearings in there as well :roll:
 
I'll definitely do an autopsy if Top Bike Kit doesn't want this bum motor back. I doubt it though. These things must cost $30 coming from the factory. I would not expect Japanese bearing in these. :lol: But I have not had trouble with Chinese bearings in the past as long as they don't get abused with water and such.

Is there any video/instructions for opening these up?
 
Comrade said:
I have never owned bike motors before, but this does not seem like an acceptable manufacturing tolerance.
Keep in mind that that is the wobble at the hub, not the rim. If, after the wheel is built up you still see that sort of wobble it's unacceptable. However that's not a given, especially if the wheel is hand built.
 
JackFlorey said:
Keep in mind that that is the wobble at the hub, not the rim. If, after the wheel is built up you still see that sort of wobble it's unacceptable. However that's not a given, especially if the wheel is hand built.

I'm not sure I understand what you mean. It seems like you are saying what the AKM "engineer" said,"finish building the wheel, it will be better". I just don't understand how a rim and spokes would improve the fact that the axle bends the dropouts back and forth.
 
Comrade said:
I'm not sure I understand what you mean. It seems like you are saying what the AKM "engineer" said,"finish building the wheel, it will be better". I just don't understand how a rim and spokes would improve the fact that the axle bends the dropouts back and forth.
If the wheel rim is true it will not be bending the dropouts back and forth. The rim's (and ultimately the tire's) relation to the axle is what determines whether you start forcing the dropouts back and forth - not what happens in between.

If you've ever built a wheel you know there comes a phase where the wheel is assembled but not trued yet. It takes a while to get the wheel fully trued on the stand. It takes me forever, but a good wheel builder will do it in 10 minutes. If that is done for a hubmotor with an out-of-true edge you have alleviated much of the problem. (May still have a brake problem if you have disc brakes tho.)

That's not to say that you should be content with an out-of-true hubmotor; by all means return it if you can. Just keep in mind that a perfectly true hubmotor with an out-of-true rim will be bending those dropouts back and forth a lot more than an out-of-true hubmotor with a trued rim will.
 
JackFlorey said:
If the wheel rim is true it will not be bending the dropouts back and forth.

That's the part I don't understand. If the bending comes from the axle mount point, which is somewhere around the base of the cassette mount, nothing except making the axle perfectly parallel to the axle on the other side would take out the wobble.
 
This is not uncommon. Many hub motors are built with poor precision tolerances, and no quality control. Usually it is the cover that is not drilled in the center. Sometimes it has a position that matches much better with the rotor, making it important to mark the cover position before removing it, in order to avoid wobbling after re-assembly.

It won’t damage your dropouts if they are strong custom torque plates or pinch type, as we recommend to do with any hub build. It is the wheel that will wobble and this will be corrected at trueing. The rotor will also need to be aligned with the caliper, with shim washers or ideally, rotor mount facing.

Maybe your motor had been opened by the customs. The cover could have been assembled at the wrong position at the factory or after inspection at customs. You could run it as is, but it is much better to find the best position in order to have the least wobble, of course.
 
MadRhino said:
You could run it as is, but it is much better to find the best position in order to have the least wobble, of course.
That is a self-help possibility, isn't it? Could try reclocking the cover(s?) to find the smoothest rotational results.

Mark one spot on the motor flange next to a cover screw, and mark each cover screw hole with a number. Try with the cover at position 1, 2, 3, etc., see which runs best.
 
Try and error is not the easiest way. Measure can save a lot of time. Alternatively, clamping the axle flat in a vise and spinning the motor will show the wobbling and let you find the middle spot.
 
Comrade said:
That's the part I don't understand. If the bending comes from the axle mount point, which is somewhere around the base of the cassette mount, nothing except making the axle perfectly parallel to the axle on the other side would take out the wobble.
If the axle is bent, then you wouldn't get a cyclic wobble - it would spin without a wobble just on the wrong axis.

If the axle isn't bent, but there's a misalignment between the axle and the motor, then the motor will wobble left and right. This can be corrected by shortening the spoke on the side of the "too close to the centerline" wobble and lengthening the spoke on the side of "too outboard" wobble.

(Again, replacing the motor is an easier way to fix it. I'd only try the above if you had no other choice.)
 
Usually, motors are too cheap to worth shipping back. Best is to show the seller a video and try reaching an agreement that wouldn’t require the cost and delays of shipping back and forth. I have done it many times, often accepting a credit on other purchases from their online store. Sometimes they will just ship you another motor, when the damage is obvious and most likely to be manufacturing defect. Customs never pay for the damages done at inspection, but the shipping companies do, when the seller has a good record for customer satisfaction or the shipping contract does include insurance. Many credit cards will refund a product purchased online and received damaged, defective, or expired shipping delay.
 
JackFlorey said:
If the axle isn't bent, but there's a misalignment between the axle and the motor, then the motor will wobble left and right. This can be corrected by shortening the spoke on the side of the "too close to the centerline" wobble and lengthening the spoke on the side of "too outboard" wobble.

That's not the major problem here, and truing the wheel won't fix the problem. The two axle bearings are for whatever reason not aligned parallel. Even if the axle and the sidecovers can withstand the abuse, the bearings will crap out very quickly from fighting against each other that way.
 
Comrade said:
[youtube]yRbe4_CVrto[/youtube]

I mounted the motor in a junk steel frame, to see what happens, and the motor has no problem bending the dropout back and forth. :(

That's no good for sure.
How's it look on the dropout on the other side of the wheel?
 
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