pF hub motor assembly with pneumatic wheel

For picoFahrrad I really wanted to keep using a pneumatic wheel like this one:

typical front wheel for a scooter, pneumatic

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”).

93mm diameter stator, 18poles (sitting on top of a 103mm 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.

exploded view of hub motor design

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:

motor can layers. Not the grooves that hold the magnets for easy gluing.

partly assembled motor can with magnets (1/2"x1/2"x1/4")

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.

2 thoughts on “pF hub motor assembly with pneumatic wheel

  1. This is really neat. Two questions:
    1) When all is said and done, the wheel will be cantilevered?
    2) When pF is moving straight ahead, will the forward axis of the drive wheel intersect the front wheel? If not, it seems like you’ll be getting some scrub and/or you’ll have to turn the front wheel off-center for it to track straight, no?

    • Hey Omari!
      1. By cantilevered, are you referring to how the axle of the motor will be supported? It will be supported from both sides.
      2. There is definitely going to be some misalignment between the planes that both wheels rotate in because the motor is on one side of the drive wheel, and I didn’t leave enough room in the fork. I’m pretty confident that by keeping the front wheel pointed straight, I will also go straight, but we’ll just have to see!

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