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John Eucist

How to ride an electric unicycle - understanding the dynamics

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Posted (edited)
1 hour ago, meepmeepmayer said:

I don't think it (directly) has anything to do with your weight in front of or behind the wheel. Otherwise, according to this logic, speeding up would get rid of wobbling. Not sure that that would work (has anybody tried accelerating like a madman to get out of a wobble?:D).

Wobbling is roll (sideways/left-right oscillation), not yaw (the wheel trying to do a curve). People don't lose control of direction in wobbles, do they? They just have trouble keeping the wheel upright in the left/right direction.

Wobbles while braking can be better explained by the fact that you're simply less relaxed and more tense on the wheel while you brake (because your leg muscles are strained because they need to push harder against the wheel than when simply standing on it at constant speed).

Its a complex issue, granted. But answer this: if wobbles are simply a matter of a strict side to side wobble then how come no one can eliminate it simply by clamping the wheel tightly between the calves?  Try it.  see if you can kill a wobble by changing nothing other than clamping the wheel tightly.  I would bet you can't. Why? because the wheel is a spinning device and there are various laws of physics at play, gyroscopic precession for one.  Tip a spinning wheel side to side and it WILL turn.  It has to. The laws of gyroscopic precession spell it out clearly.  I put a video up here once showing that, but you tube is loaded with scientific explanations.  How all these forces interact with each other is difficult to determine. I don't know why clamping doesn't eliminate wobble.  I get wobbles climbing hills at speed, I believe this is also because the contact patch of the tyre (far in front this time) is a long way from the rider's center of force.  The further apart these two point get, the less stable the ride.

"People don't lose control of direction in wobbles, " precisely because it IS a wobble, every change of direction of the wobble cancels out any direction change of the previous cycle of the wobble. 

"speeding up" does not get rid of wobble because you have separated tyre contact patch and rider's center of effort, only this time the other way around.

 

EDIT: try this experiment:  place your feet several cm behind your usual position, then ride around, make some turns, etc.  Does it feel stable of does it feel twitchy?  No?.  Move them further back and try again.  At some point the behavior of the wheel will be very strange and dangerous.  I'm not sure anyone without extra long pedals could repeat the experiment by placing the feet unusually forward.  I have such pedals.  Maybe I'll try it.  But not this week, the weathers, fixing to go to shet.

Moving the riders centre of effort away from the centre of resistance (contact patch) causes instability.  This is exactly how to steer a sailboard; move the center of effort (the sail) behind or in front of the centre of resistance (the centerboard) causes a change of direction.

Edited by Smoother

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Posted (edited)

A fatter wheel so that your legs are further apart would reduce wobble. Maybe even a half-moon shaped inset where your legs clamp onto the sides of the wheel would help as you could dampen out the tendency to spin around the contact patch. A fatter tyre would also help.

Edited by Nic

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10 hours ago, Smoother said:

But answer this: if wobbles are simply a matter of a strict side to side wobble then how come no one can eliminate it simply by clamping the wheel tightly between the calves?

10 hours ago, Smoother said:

I don't know why clamping doesn't eliminate wobble.

I'd say: Because you're already wobbling. The wheel is already going sideways (literally and figuratively:P). In order to stay balanced riding a EUC, you constantly and actively have to balance with your feet to negate all the tiny (or big) influences trying to make the wheel fall over sideways. So clamping does not remove wobble for the same reason simply clamping the wheel while it is falling over sideways does not keep it upright. It's too late for that.

Otherwise new riders could just stay on a still wheel by grabbing it hard. Doesn't work (but who hasn't tried);) You can't pull yourself up by your own bootstraps.

-

Not sure about your center of effort theory. I'd rather hold an "unnatural" and tense stance responsible for the appearance of wobbles then. Fo example, according to your theory, you should no longer have wobbles going uphill if you put your feet further forward (closer to your contact patch). Does that work?

But who knows. And since this is not a wobble thread...:)

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I've had wobbles in different scenarios going fast i just reposition, this is my brake wobble i knew it was wobbling but never thouht it will throw me off  i just don't let them bother me to much just ride them out one way or another

 

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Posted (edited)
1 hour ago, meepmeepmayer said:

Not sure about your center of effort theory. I'd rather hold an "unnatural" and tense stance responsible for the appearance of wobbles then. Fo example, according to your theory, you should no longer have wobbles going uphill if you put your feet further forward (closer to your contact patch). Does that work?

No it doesn't help and here's why.  To climb a steep hill ones feet have to be unusually far forward in order to transmit the desired amount of power into the pedals to raise your weight up the hill, or one just stops or slows to a crawl.  It is because the centre of effort is so far form the contact patch (even though the contact patch has moved slightly forward) only this time its in front not behind.  I'm not sure what physical law is at work here because it clearly isn't reverse castor, but it's also not a wobble it's a weave (I should have made that clear a few posts ago) but the weave is uncomfortable and gets worse the faster I go (the further forward of the contact patch I put the centre of effort.

As for clamping, I have no trouble keeping the wheel upright AND clamping the hell out of it.  I don't need to be dancing on the pedals all the time, to maintain balance. But no amount of clamping (and not dancing on the pedals) will stop a wobble.

52 minutes ago, stephen said:

I've had wobbles in different scenarios going fast i just reposition, this is my brake wobble i knew it was wobbling but never thouht it will throw me off  i just don't let them bother me to much just ride them out one way or another

That is quite a severe wobble, but you only braked for less than 2 seconds. That would bother me, because I know the wheel is trying to throw me off.  If you were slowing from a higher speed and having to slow to a dead stop, it probably would have got worse, or at least caused you to reduce the amount of braking force, in order to keep the wobble from amplifying, therefore increasing the braking distance over what you had intended..  I'd suggest you try it, but I don't want to be the reason you (might)  come off at speed. 

Ps I've seen that before, even played it back a few times. That was when that person and dog walked straight out into your path.  A bit of a high pucker factor moment, I'm sure.

Edited by Smoother

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Phew that was a scary wobble. I got a similar wobble yesterday when cruising down a light incline and then hit a few bumps and slowed down.
I have 2 different ways of slowing down.

1. Squeezing the pads between my legs and sitting back or leaning back.
2. Opening my legs and letting the wheel come out in front of me.

Option 1 works best for quick braking and option 2 works best for very slowly going down steep hills. Option 2 is the wobbly one for me.

However... as we ride more and more we will push the threshold for wobbling further.

I have tried different wobble situations as well and can minimise and reduce wobble by bending my legs a bit and carving it out.

Regarding the whole speed thing. If I am in a clear area I will speed up carefully and play with the speed. I can hit 30km/h for short bursts and sometimes touch on 35km/h.
For now this is enough for me.

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Well done, and welcome.

You have picked a path that almost no one would have recommend, but you did it, and you're here (an EUC rider) so the result is the same.

If you don't have any yet, get your protective gear sorted out before you break something, and wear it. You never know when you're going to fall. I fell on my ass today, crossing a simple step up from one level to another at no speed, after riding miles of rutted farm land in vicious cross winds with no issues.  Nothing broken but my ass was sore for a few minutes.  It might still be sore tomorrow.

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Don't worry, i've got the full monty, from top to toe, even ankle protection ...

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