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I have replaced a damaged planetary gear in my rear hub motor and faced the following issue: when powered, the rotor rotates, but somehow the wheel does not (or rotates very slightly). When I open the casing on the side where the planetary gear sits, I can see that when the wheel is manually rotated, the rotor and the planetary gear rotate accordingly (in the way one would expect for both the forward and the backward directions). However, the rotor, when powered, can't give enough torque onto the wheel (I can hold it by just pressing a finger against it, while the rotor rotates vigorously), so there is some engagement issue, yet I just can't figure what it is. The contact between the new planetary gear, the sun gear and the ring gear is reasonable tight, although there is some wobbling (which is significantly, if not completely, reduced once the covers are mounted onto the shaft). The wiring is correct (again, the rotor rotates smoothly once out of the casing).

It feels like there is some part missing, but I do not see any. The existing weak rotation of the wheel feels like it happens purely because of the friction somewhere in the system.

Other symptoms are: the motor humms rather loudly when powered (I do not remember whether it was as loud before, but it is significantly louder than the other bike), and also once the rotor get up to speed, it makes some clanking sounds more or less regularly (but no debris caught between it and the casing, and rotates smoothly once out of the casing).

What should I look into here and what are the probable cause?

Below are some pictures.

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  • Could it be that your sun gear is slipping on the axle when you put some resistance to the wheel? Also, stating what make and model motor you have might help finding the correct answer.
    – Burki
    Commented Oct 31 at 9:31
  • @Burki The sun gear is bolted to the rotor, so they rotate around the axle together synchronously. As for the manufacturer, I couldn't find any labels that would tell me that apart from the characteristics along with some number: PY48V26"16115608 — does not show up in Google.
    – Andrei Smolensky
    Commented Oct 31 at 18:00

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In the end it turned out that "rotate in the way one would expect" was a bit of an overstatement. The issue turned out to be that the clutch in the new planetary gear carrier is counter-clockwise, while the old one had it clockwise. Nearly impossible to tell in advance since in online stores they (almost?) never write which way their items are and most of the models lack markings (this one does, surprisingly, but it was not featured on the store page).

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