Just added some numbers to the cutting plane in my previous post to facilitate the description.
1: urethane wheel
2: front cover
3: back cover
4: motor can (rotor)
5: anker (stator)
6: stator insert
7: stator endplate
8: axle (cast aluminium)
9: clamping sleeve
10: mounting nut
12: front bearing
13: back bearing
Rotor and Wheel
I wanted to move the complete motor as far as possible inside the wheel (1) to get a minimum protrusion on the back part of the hub motor but also to maintain the trackwidth. Therefore the red anodized rotor cover was completely turned off the motor can. This has to be done quite carefully, in ordern not to damage the magnets.
This opened up the possibility to make a complete redesign of the front cover (2), bearing a bigger (bigger than the usual 8 mm ones) front bearing (12) while giving it a nice looking front too. The fixed bearing (12) is held in place by the circlip (11).
The urethane wheel was completely drilled out with the diameter of the motor can. So the only way to fixate the wheel on the rotor can was using adhesive. This was the price I had to pay in order to move the motor as far as possible inside the wheel, so that there is nothing left from the former inner structure to get the inner motor hooked on the wheel. For bonding I choose uhu endfest 300 which seems to be strong but also elastic (at least until now). I read a lot in the forum about the slipping urethane issues some of you guys had so far. Imho the shiny surface of most outrunners, eventually together with a low number of “bumps” are not the best basis for a good adhesing, very durable connection. So I was lucky, that the older APS rotor cans have numerous groves on their outer surface - this is what adhesive needs. In addition to that I also sanded off the black coating on the can to a certain extend. I also thought of applying heat during the curing process to further strengthen the bonding but I didn’t. I didn’t want to weaken the magnets by applying a too high temperature. To conclude, so far I never had problems with slipping urethane - but I will keep my fingers crossed.
Now for the back cover (3) of the rotor. Normally, having an outrunner where the radial forces act on the rotating axle you have an open end. For the hubmotor you have to support the radial forces acting on the outer rotor not only from the front but also from the back. The back cover (3) which is indeed more like a sleeve, is also glued to the outer surface of the motor can. Last but not least, the back cover bears the large “loose” bearing of the hubmotor.
Back and front cover are having several cooling slots to account for the generated heat inside the motor. By the way, the front cover is also glued to the rotor but to the inner surface of the motor can.
This is how it looks when assembled right before the wheel is fitted:
And finally with wheel: