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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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(Still waiting for my KS18XL to arrive)

There is a somewhat popular you tube guy named Hsaing. He hit a diagonal rut in the road and went down (https://www.youtube.com/watch?v=tPaMRVRW7u8). Crash happens at 9:30 in the video.The thing I noticed watching his videos during his rides is that his leg is not pressed up against the side of the EUC and at times the it looks a bit wobbly. I'm thinking that part of the reason he crashed is that his connection to the EUC is not solid, and so when he hit the bump it had an outsized effect. 

What do you guys think?

Watching another video, it seems like when you start to lose you balance, inexperienced people try to tilt the wheel to get it back under themselves--but this is too slow. Basically when you are losing your balance to the side, your center of gravity is not directly over the wheel. If you twist, you CG is still not over the wheel, but now the wheel notices that you are tilted forward and it accelerates to get back under you. That's why twisting works better to regain balance that tilting. (Tilting is fine for turns.)

I mean, for this to really work, you have to get it into your muscle memory. But at least if you *try* to do the right thing to regain balance, that process will move forward.

 

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Posted (edited)
15 hours ago, erk1024 said:

The thing I noticed watching his videos during his rides is that his leg is not pressed up against the side of the EUC and at times the it looks a bit wobbly. I'm thinking that part of the reason he crashed is that his connection to the EUC is not solid, and so when he hit the bump it had an outsized effect. 

What do you guys think?

I would say most experienced riders make little contact with the wheel above the feet.  A death like grip on the wheel is mostly a rookie crutch to try and control severe wobble caused by lack of muscle memory.  Once you know how to ride, I for one, try to have as little calf contact as possible.  I even adjust my feet outwards if I feel excessive contact in that area, after mounting, etc.  Clamping is also used to grain more control of the wheel over rough ground or hills, but this is "Power" control, not directional control. In my experience you cannot clamp your way out of a wobble fall.  He is obviously an experienced and confident rider (Manhattan traffic, former inline skater w/tricks).  Yeah, his left foot has a particularly funky placement, but he rides well.  Once that wobble started, almost no one could have prevented the fall.  Maybe if he wasn't holding a camera/selfie stick he might have had more use of his arms to "flap" his way out of it.  Hard to say.

One thing I did note; This supposed rock solid stability of the Z10, is just a myth.  It may not want to lean over in fast corners, but it will wobble crash as well as the next wheel.

Edited by Smoother
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2 hours ago, Smoother said:

One thing I did note; This supposed rock solid stability of the Z10, is just a myth.  It may not want to lean over in fast corners, but it will wobble crash as well as the next wheel.

To add to this. The Z10 is very different than other wheels. It has a very wide tire. You usually ride on the center or the tire. When the fat edge of the tire catches something it can cause unexpected strong movements. The tire also tends to bounce. Hitting something at an angle can also cause problems. This said, he had just got the wheel and was still getting used to it.

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13 hours ago, erk1024 said:

I'm thinking that part of the reason he crashed is that his connection to the EUC is not solid, and so when he hit the bump it had an outsized effect. 

What do you guys think?

It's a somewhat weird crash and it looks more like coming from an overcorrection than from a lack of control. The street configuration doesn't look at all problematic to me, but I also don't ride the Ninebot Z10.

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Posted (edited)
5 hours ago, RockyTop said:

To add to this. The Z10 is very different than other wheels. It has a very wide tire. You usually ride on the center or the tire. When the fat edge of the tire catches something it can cause unexpected strong movements. The tire also tends to bounce. Hitting something at an angle can also cause problems. This said, he had just got the wheel and was still getting used to it.

I commented on this phenomenon when I did the 2.5" mod to my KS16. The desire of a wide tire to follow a raised, or lowered ridge is quite dramatic.  And yes, the wider the tire the more severe the effect when riding over an uneven surface that more or less parallels one course.  The solution; just like on a bike or motorcycle, is either to avoid the area, or to cross at an oblique angle (as close to 90 deg as possible).

Edited by Smoother
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3 hours ago, Smoother said:

The desire of a wide tire to follow a raised, or lowered ridge is quite dramatic.

Yes, but in this case the initial movement of the wheel was rather to the right, hence to the opposite than following the groove.

 

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Posted (edited)
10 minutes ago, Mono said:

Yes, but in this case the initial movement of the wheel was rather to the right, hence to the opposite than following the groove.

Well spotted.  I have no idea what forces actually too place.  My original statement about the fall was:

10 hours ago, Smoother said:

One thing I did note; This supposed rock solid stability of the Z10, is just a myth.  It may not want to lean over in fast corners, but it will wobble crash as well as the next wheel.

The line following this was a response to @RockyTop s post.  But you're right.  In theory it should have tipped left  Maybe he was at a suitably oblique angle and it was the bump it self that did him in.  He wasn't exactly following the line, it was more like 45 deg., but the bottom line is a Z10 can tump the rider off despite its' "stability"

Edited by Smoother

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I don't know about the stability, but the hopping I have seen in several vids doesn't fuel wheel control. There are also a few AFAIR similar Z10 wobble crashes on vid.

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Thanks for the replies!

It's hard to tell what unbalanced him. The groove he hit wasn't very deep at all. I wonder with a wide tire, if you hit a lip at a 45 degree angle and it hits the wheel on the right, if the wheel in this case wants to get rotated towards the right--unbalanced force. I don't know. But the moral is probably try to hit a groove perpendicular if possible. On a bike you always want to cross railroad tracks perpendicular. Those things are slippery!

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On 3/5/2019 at 9:33 PM, travsformation said:

Hard to say, depends on a ton of factors (rider, wheel, etc.). I never got speed wobbles on the V8, the only wobbles were when going down very steep hills (feet positioning solved that). 

On the 18XL, I do get them. For now I push the envelope from time to time to force them upon myself and learn to deal with them. Sometimes I try to relax, sometimes I carve, sometimes I grip the wheel and sometimes I chicken out and slow down. I'm guessing time and miles will sort that out. 

So upgrading to a new, bigger and heavier wheel can cause speed wobbles (for some people). All the same, I just see it as part of the process. As long as one is cautious, doesn't push it beyond his skill level / comfort zone / running speed (and gears up properly!),  it shouldn't be too much of an issue. Or at least, that's my experience.

And when I'm doubt, ask the community :) (preferably after having slowed down and stepped off your wheel) :efee612b4b:

Hi, could it be contributed to by the wheel actually wobbling like mine?

 

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Posted (edited)

I'm trying to find the link to a blog I found here that had lots of articles with tips, even graphical drawings, showing the correct "monkey position", carving in a straight line while breathing, and things like that. Can't find it for now. 

EDIT

Found it, I recommend it: https://eucriding.blogspot.com/

Edited by Jean Dublin

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[I posted this question in another thread, but thought it made more sense here]

Could you tell me more about "overleaning". Obviously you can lean forward too dramatically and no wheel in the world would be able to catch up. But what happens in this situation? I'm imagining the wheel trying to surge forward, which re-levels the pedals, but as the rider you fall off the front edge of the pedals because your CG is over-extended. Or does the wheel sense the situation and the motor cuts out?

I think I understand the fast-speed overlean. I've seen a video where someone was going past the max speed of the wheel, the alarms were beeping like crazy. The rider had disabled tilt-back, and couldn't hear the alarms because of wind noise. Eventually the wheel couldn't keep up and the guy faceplanted off the front. 

But I imagine it's possible to overlean at low speeds, in which the wheel is trying to correct the out of balance, but the rider's CG is just too far out over the front. 

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Overlean = Faceplant

 

You ask for more power than it has to give, boom hit face. This applies at any speed. If you're heavy enough and try to accelerate fast enough, it will just drop you. This can happen at 0 mph and whatever the max speed is if you give it the right conditions. 

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10 minutes ago, erk1024 said:

Could you tell me more about "overleaning". Obviously you can lean forward too dramatically and no wheel in the world would be able to catch up. But what happens in this situation? 

One has a max torque over speed limit with BLDC motors. A straight line between (maximum stall torque, 0km/h) and (0 Nm, maximum no load speed).

This limit line is proportionally "moving" with battery voltage.

Whenever one hits this limits (asking more than this max torque at a given speed) the motor cannot supply this torque and one overleans. The lower the speed the more "asking" torque/acceleration/forward leaning is needed...

More details can be found here:

 

 

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4 hours ago, erk1024 said:

I'm imagining the wheel trying to surge forward, which re-levels the pedals, but as the rider you fall off the front edge of the pedals because your CG is over-extended. Or does the wheel sense the situation and the motor cuts out?

both may happen (though the latter should not, in particular with modern wheels), or the motor just runs out of torque. Which one happens depends on the motor power (i.e. available torque), possible current limitations, the pedal length, and the speed, because the available torque (and current) decreases linearly with increasing speed which makes riding at the speed limit particularly delicate and dangerous.

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7 hours ago, erk1024 said:

you fall off the front edge of the pedals because your CG is over-extended.

If you are wondering about wether the pedals stays level and the rider just tips over because of a lost footing, no, that can’t quite happen on level ground.

You might’ve seen extreme accelerations in videos. While the rider’s CoG is well past the front of the pedals, if the rider would start to fall off the front of the pedals, all his weight would be at the very front edge of the pedals. The only way for the wheel to stay level in general is to fight the tilt with acceleration. It wouldn’t stay upright if it would accelerate any less than what is required to catch the rider’s lean.

If the wheel doesn’t have the power to accelerate fast enough, it will tilt forwards, pedals and all. This is when and how the crash by an overlean happens. Once the tilt reaches ~45 degrees, the wheel is programmed to turn off the motor. Although, by that time the rider has already fallen or bailed.

Sudden obstacles are another matter though. If the wheel hits a pothole, sinks in sand etc, the speed of the wheel is reduced even if the wheel is succesful in staying upright. But there is nothing to slow down the forward leaning rider. The rider is not prepared and the ankles are loose, so the rider doesn’t get his weight on the front edge of the pedals in time. No weight = not enough acceleration, so the rider falls on his face while the wheel stays upright.

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