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Ninebot Minipro Knocking/Thumping Sound + Fix

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I've been riding my Ninebot minipro for a little over a year now and recently encountered an issue with a knocking/thumping sound coming from the right side wheel.  The sound is pretty loud, happens about once per revolution, and you can actually feel it in your feet when riding.  I dug around and I believe it's the same issue that's mentioned in this thread:  

I never did see a detailed solution posted so I figured I'd document what I did to fix my wheel.  First off, the sound seems to be due to the wheel being slightly loose on the axle.  As shown in the video in the other thread, if you pull/push on the broken wheel it should move slightly.  On the good side the wheel is very tight and does not budge.

I disassembled my wheel by first popping off the 4 tabs on the plastic wheel cover, unscrewing the screws beneath, and then removing the plastic wheel cover.  Underneath is a black metal disk that covers the coils/hub motor secured by 6 screws.  The black metal cover is also what holds the wheel on tightly, and ideally should also be pressing tightly on the bearing beneath.  For some reason my cap wasn't doing that.  I also noticed that my bearing was very tightly stuck on the axle, in fact I wasn't able to dislodge it at all.  I suspect it might have gotten pressed down by half a millimeter.
I don't have pictures but there are a few floating around on the internet in various disassembly threads:  https://forum.electricunicycle.org/topic/5474-ninebot-mini-motor-problems/

Anyways, what I did was unscrew the cap and put a thin ~35mm bushing into the cap so that it presses firmly against the bushing again.  If you're having trouble getting the cap off with the screws unscrewed, try lightly tapping the cap to rotate it.  Once it's rotate a few degrees you can pry it off with a screwdriver under one of the wings. 
For the bushing, I actually just took some measurements with a caliper and just cut a ring out of an aluminum can.  Kind of ghetto but it solved my problem.  I suspect dislodging the bushing from the axle and reseating everything might have worked too, but I wasn't able to do that.  With the bushing in place, I screwed the cap back on with some loctite.  If you're having trouble seating the cap properly, loosely seat all 6 screws and slowly tighten them in 1 turn at a time.

Hopefully this helps someone, my Minipro was practically unrideable before but now it's perfectly good again.


Edited by mythe00
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3 hours ago, mythe00 said:

I actually just took some measurements with a caliper and just cut a ring out of an aluminum can.  Kind of ghetto but it solved my problem. 


Good to hear that you figured it out and found a solution. :cheers:

You can buy shim stock, however  aluminum cans are used quite often in the professional world too. When asked how thick would you like your shim stock a common answer is, “ I don’t know. How thick is an aluminum can?” :rolleyes:

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