In-wheel suspension

  • #1
jack action
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This suspension within a wheel looks really nice (source):
 
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  • #2
berkeman
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There was a thread recently where another poster was trying to figure something like this out. I'll see if I can find it.

Obvious issue with this design is the penalty in unsprung weight, it would seem...?
 
  • #3
berkeman
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Oops, that thread was about putting the whole motor inside the wheels...
Summary: a central motor, inside the wheel, fixed to the frame. the wheel goes around the outside, but can also move up and down for suspension purposes. how best to transfer the drive?

I'm brainstorming how to make an electric motorbike, making as much use of the available space as possible to allow for as many batteries to be fitted as possible.

Batteries aren't relevant right now; my focus is on the final drive at the back of the bike.

To maximise space, I want to fit the motor inside the rear wheel - this seemed the sensible place for it, it's already round and it's where the drive needs to go. it also means one less chain / transmission to worry about, and can help make the overall look of the bike a lot cleaner.
 
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berkeman
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Obvious issue with this design is the penalty in unsprung weight, it would seem...?
And maybe the main issue would be the increased wheel weight and MOI, as opposed to unsprung weight. Accelerating that puppy is going to take some extra work!
 
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anorlunda
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I agree that it looks nice. But it is hard to believe that it hasn't been tried before. Maybe you could find earlier attempts or even patent applications.
 
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anorlunda
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And maybe the main issue would be the increased wheel weight and MOI, as opposed to unsprung weight. Accelerating that puppy is going to take some extra work!
That may not be a big deal for all users. Lots of us like to ride slowly. In developed areas, the bumps at curb cuts and sidewalk seams are an annoyance.
 
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jack action
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Obvious issue with this design is the penalty in unsprung weight, it would seem...?
And maybe the main issue would be the increased wheel weight and MOI, as opposed to unsprung weight. Accelerating that puppy is going to take some extra work!
As for the unsprung weight it's quite the opposite, it's at its minimal value (the rim and tire).

But I didn't think about the MOI and that is certainly a negative factor.

What I find also interesting is that the suspension geometry affects only the vertical motion, which is what it is supposed to do (no toe, camber, caster change or tire scrub as it moves up & down). But it might also become problematic to handle lateral forces in extreme cases.
 
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Also, the suspension components are cycling constantly due to vehicle weight, even when rolling on a flat surface. Sounds like a lot of extra wear and tear.
 
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anorlunda
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Also, the suspension components are cycling constantly due to vehicle weight, even when rolling on a flat surface. Sounds like a lot of extra wear and tear.
Now that's an interesting point. If they cycle and dissipate heat constantly, then it becomes more like an exercise bike.

Nevertheless, I still think that a class of users including wheelchair users and old folks who ride slow but who worry about curb cuts and broken sidewalks, that might value shock absorption more than bicycle efficiency or acceleration. For example, the wheel moving to absorb a 4cm bump with little or no vertical motion in the bike's frame.

It is a niche market, so the value of the idea should be judged in that context.
 
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Typical, it looks like there's a solution to my problem and I can't view it because it links through faceache! I'll have to have a look when I get home from work...
 
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As for the unsprung weight it's quite the opposite, it's at its minimal value (the rim and tire).

But I didn't think about the MOI and that is certainly a negative factor.

What I find also interesting is that the suspension geometry affects only the vertical motion, which is what it is supposed to do (no toe, camber, caster change or tire scrub as it moves up & down). But it might also become problematic to handle lateral forces in extreme cases.
I think that it does change caster. When the suspension compresses, the effective radius of the wheel is reduced (assuming compression due to a bump at 6:00). The center of rotation (hub) and the center of curvature (wheel) aren't the same (until the suspension recovers).
 
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