For picoFahrrad I really wanted to keep using a pneumatic wheel like this one:
It is a larger wheel than what you might normally want to put a hub motor in because the gear reduction on the motor would be so large. So I went with a larger 93mm stator (103mm is also available for purchase on ebay, search “atv stator” or “quad stator”).
So the idea is to have the motor hanging off the side of the wheel since there is not enough room in the middle because the inflated tube takes up so much space.
The 6 layers are made from flat stock that are waterjet. Only the 2 layers with magnets are made from steel, the rest are aluminum because its easier to work with. An adapter fixes the stator to the axle. Two bearings, one on the front (visible) and one on the other side of the wheel (not visible) support the wheel and the motor can as it spins about the axle.
Here are some of the actual waterjet parts:
The steel layers are cut with grooves that hold the magnets, which will make gluing magnets in with even spacing much easier. This design was inspired (actually, pretty much just taken) from Kitmotter.
I think I might turn the entire outside of diameter of this assembly when I am done, just to make it extra shiny. Also, I cut the steel layers out of cold-rolled steel bar stock, and when they came out, they were slightly bowed. I guess there was quite a bit of internal stress. When I tighten the screws down, this shouldn’t be an issue, but I guess just be aware that may happen if you are using cold-rolled stock.