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Electric unicycle and bicycle dynamics - gyro effects on steering


rcgldr

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3 hours ago, Eucner said:

Yes, I did. Thanks for reminding me to report my findings. At the first I decided to do it slowly. It turned out to be a large yaw angle movement and a strong moment. I was surprised. I was waiting for more subtle response. This assured me that I'm on right track with autocorrection.

Interesting that your findings are so different from mine. Could you shoot a video where a slow tilt causes a strong yaw?

Which wheel did you do the test with? And at which speeds?

 

Either way, while it seems that @Eucner is alone in believing the precession theory, none of us seem to have the tools to explain or prove our stances in a way that couldn't be explained by the other theory as well. We'd need for example a very light tire vs a heavy tire with a similar profile, or something else. Without more  controlled tests this discussion is going nowhere.

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9 minutes ago, mrelwood said:

Either way, while it seems that @Eucner is alone in believing the precession theory, none of us seem to have the tools to explain or prove our stances in a way that couldn't be explained by the other theory as well. We'd need for example a very light tire vs a heavy tire with a similar profile, or something else. Without more  controlled tests this discussion is going nowhere.

Perhaps have a look at racers racing on a track. Zen Lee have videos with really good shots of racers cornering hard. What I find interesting is how the wheels stay so vertical, relatively speaking, in the turns.

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1 hour ago, mrelwood said:

Interesting that your findings are so different from mine.

Which wheel did you do the test with? And at which speeds?

I did it little differently. I lifted my V8F with only tree fingers, so it was free to rotate, and raised my knee to tilt the wheel against it. I tried to use my normal turning speed for tilting. I did let it accelerate to full speed, which took about 3-4 seconds. Tilting started as soon as I could raise my knee and stopped about halfway of acceleration.

1 hour ago, mrelwood said:

Could you shoot a video where a slow tilt causes a strong yaw?

I'm sorry, no published videos now with my skills and schedules.

1 hour ago, mrelwood said:

Either way, while it seems that @Eucner is alone in believing the precession theory, none of us seem to have the tools to explain or prove our stances in a way that couldn't be explained by the other theory as well. We'd need for example a very light tire vs a heavy tire with a similar profile, or something else. Without more  controlled tests this discussion is going nowhere.

Sadly true. You felt how strong the gyroscopic precession is and still don't believe in it. I also provided a link to a discussion on scientific forum and youtube test video. In broader concept I'm not alone. 

I went for a ride to observe roll and yaw angles. Rolling the wheel lead to a yaw angle change like it was geared. I didn't feel any tendency from cone effect to make tighter or loser turning radius. Maybe I'm not skilled enough rider. I also tried to test isolated cone effect, but it was so weak that things like wheels front-tail mass distribution and lack of hand coordination easily overruled it.

For a reminder, here is my initial claim.

On 7/31/2022 at 3:05 PM, Eucner said:

Gyroscopic precession has many times been considered to be too weak to be meaningful for EUC riding. This video showed that it might have more meaning than thought before. I'm certain camber effect alone is not enough explain autocorrection of the wheel we have seen on the trick ride videos and experienced ourselves. In combination with gyroscopic precession it could make it.

I do believe in cone effect and gyroscopic precession. Others here seems to believe only in the former one, despite all the evidence and possibility for self test. I understand that many of you have previously neglected gyroscopic forces and it can be too hard to admit it.

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5 hours ago, rcgldr said:

Walk the dog and Davastato demo:

I watched the video few more times. What caught my attention was the almost chaotic nature of the loose wheel. Adam is very skillful rider and I believe he can release the the wheel with a good consistency. Still the wheel seemed to have its own mind. It could go steadily straight, make a large turn, make tight U-turn, make a L-turn, wobble or a combination of these. This kind of restless behavior happens when there is multiple phenomenon's acting simultaneously. Individually a phenomenon can be very predictable, but their combined effect looks random.

Edited by Eucner
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I love this topic!

I have learned: 

This is very complicated and my head just will not fit around it.

I hope:

As the discussion continues, maybe it'll get said in just that one special way that my ah-ha! bulb goes on and just like that I'll really understand how a helicopter really works.

But alas:

It remains as obvious to me as directional radio antenna arrays, and only slightly more mysterious than imaginary numbers (although I do claim to understand those).

Nevertheless... I love this thread!

 

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1 hour ago, Eucner said:

I watched the video few more times. What caught my attention was the almost chaotic nature of the loose wheel.

Take a look at the one with the dog on the EUC again. It changes tilt a few times because dog is moving, then goes straight once the dog stops moving.

https://youtu.be/MBtSQHT3CCo

1 hour ago, Eucner said:

I do believe in cone effect and gyroscopic precession. Others here seems to believe only in the former one, despite all the evidence and possibility for self test.

Wrong Way's video comparing typical EUC with street tire, Z10, and a typical EUC with knobby tire shows tire parameters and the related camber effect are the primary cause of the response to tilt, as the wheels are of similar weight. 

https://www.youtube.com/watch?v=NsXW4OKnmWc&t=314s

As for the amount of yaw torque (resistance) versus yaw movement (no resistance) it appears to be relatively small in the next video. The professor in this video states there's no angular momentum involved with precession. An 8 lb gyro supported at one end is spun up to several thousand rpm, then assisted to precess with the axis somewhat higher than horizontal. A small peg is placed in a hole to stop the other end of the gyro, and the gryo stops precessing and drops down as if there was near zero angular momentum, near zero precession torque, while bouncing back a bit.

https://www.youtube.com/watch?v=0L2YAU-jmcE&t=3104

I still don't know how to quantify precession induced yaw torque (which would require resistance, such as contact patch friction and angular inertia of the non-rotating parts of EUC and rider), versus precession induced yaw movement (no resistance). The relatively large rotors and high power to weight ratios on radio control helicopters are able to generate significant precession roll and yaw torques that roll or yaw the entire model, but it's a huge amount of angular momentum. A TREX 700's aerobatic (idle up) 62 inch | 5 1/6 foot long rotor speed is 2200 rpm, equivalent to rolling at 405.8 mph.

On my motorcycle, a 2001 Suzuki Hayabusa, I don't get much of a sense of resistance (angular momentum) to counter-steering inputs to the handlebars until I'm going 50 to 55 mph. On an EUC with a heavier wheel than my bike's front tire, maybe for an EUC it shows up at around 40 mph (just a guess on this). The Wiki article on counter-steering claims that at 40 mph, the initial reaction to the rider steering outwards results in a precession induced inwards roll torque that is about 12% of the roll torque, with 88% of the roll torque due to lateral friction forces at the ground as the tires track outwards. However, this is based on a single source, with no description of the bike or how much counter-steering torque the rider applied to the handlebars to lean the bike.

https://en.wikipedia.org/wiki/Countersteering#Gyroscopic_effects

 

Edited by rcgldr
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42 minutes ago, rcgldr said:

Slow speed tight turns via tilt steering, camber effect. I doubt there is any significant precession effects when the speed is this slow:

Yes, probably not. The gyroscopic precession is weak at low speed. To be sure we should calculate it. What you try to prove? I'm having nothing against the cone effect. It just isn't the only force in the equation.

Edited by Eucner
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3 hours ago, techyiam said:

Perhaps have a look at racers racing on a track. Zen Lee have videos with really good shots of racers cornering hard. What I find interesting is how the wheels stay so vertical, relatively speaking, in the turns.

In EUC racers on pavement, the EUCs are tilted so much that pedal scrapes are a limiting factor. This is why Chooch Tech chose a V12 with the pedals at the highest setting (more pedal clearance). Due to lateral loads, the contact patch flexes inwards, increasing the radius of turn in response to tilt, so more tilt is needed.

https://www.youtube.com/watch?v=mdI_xCnDzHk&t=212s

 

Edited by rcgldr
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1 hour ago, rcgldr said:

In EUC racers on pavement, the EUCs are tilted so much that pedal scrapes are a limiting factor. This is why Chooch Tech chose a V12 with the pedals at the highest setting (more pedal clearance). Due to lateral loads, the contact patch flexes inwards, increasing the radius of turn in response to tilt, so more tilt is needed.

Notice some of the racers at certain times.

Use slowest playback speed, and in portrait mode. Time-stamped 

 

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Actually, I may have figured a way! This question is especially directed to @Eucner:

Since you believe that precession is a notable yaw force when turning with EUCs, do you feel the EUC turning tighter at the start of the turn, compared to a long mid section of the turn with a steady roll angle? If you do, which wheel would that be with, at what speed, and how tight/long a turn?

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1 hour ago, mrelwood said:

Actually, I may have figured a way! This question is especially directed to @Eucner:

Since you believe that precession is a notable yaw force when turning with EUCs, do you feel the EUC turning tighter at the start of the turn, compared to a long mid section of the turn with a steady roll angle? If you do, which wheel would that be with, at what speed, and how tight/long a turn?

I think with my T3 with stock tires, it should be mostly camber induced turning.

However, with my V12 mounted with a scooter tire, I think I may able to test whether I can invoke roll induced precessional yaw turning. I think I wiil experiment at the start of a turn.

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5 hours ago, Eucner said:

I did it little differently. I lifted my V8F with only tree fingers, so it was free to rotate

Then how did you assess the strength of the yawing force?

When riding, we have our whole weight on and covering most of the pedals. If the precession is strong enough to matter, it has to be strong enough not to be able to counter just by holding the handle tightly.

 

5 hours ago, Eucner said:

You felt how strong the gyroscopic precession is and still don't believe in it.

Believing or not in a scientific fact has no place in technical discussions. Yes I "believe in" gyroscopic precession. I pray to it's might every day.

As you reminded, were talking about whether that force is strong enough to matter when riding EUCs. And whether it makes a difference in auto-correcting an EUC. You are certain that it does, the rest of us seem to think that it doesn't.

5 hours ago, Eucner said:

I went for a ride to observe roll and yaw angles. Rolling the wheel lead to a yaw angle change like it was geared.

That's exactly what the cone effect does. Or did the yaw angle stop changing once the roll angle stopped changing during a longer turn?

Have you ever ridden an EUC with a 3" tire width? The turning behaviour is from a different planet to your V8F. And it applies to 22", 18", 16" and even 10" diameter 3" tires. They turn and stay upright in a similiar fashion to each other despite the weight difference being huge. Precession changes with mass, so shouldn't the difference in yaw behaviour be huge between a Mten and a Monster? Since it isn't, there's reason to believe that precession is too small a force to matter when riding an EUC (at under 50km/h).

Also a knobby tire yaws, rolls, wobbles, and self-corrects very differently to a non-knobby of a similar weight. Why is this? Precession should be identical.

 

5 hours ago, Eucner said:

I didn't feel any tendency from cone effect to make tighter or loser turning radius.

Precession only yaws when the roll angle increases, so during the  initiation of a turn. Once a stable roll angle has been achieved, precession stops yawing. Do you feel the precession stopping when you reach the intended roll angle? Does the wheel yaw more during the beginning of a turn?

5 hours ago, Eucner said:

I also tried to test isolated cone effect, but it was so weak that things like wheels front-tail mass distribution and lack of hand coordination easily overruled it.

So many questions. 1) How did you try to isolate the cone effect? You commented on my turning video that precession is strong enough already at walking speeds. 2) How do you determine the strength of the effects of the wheel's mass distribution compared to cone effect?


Ps. I didn't see any auto-correcting happening in the coin video.

Edited by mrelwood
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5 hours ago, rcgldr said:

I still don't know how to quantify precession induced yaw torque (which would require resistance, such as contact patch friction and angular inertia of the non-rotating parts of EUC and rider), versus precession induced yaw movement (no resistance). The relatively large rotors and high power to weight ratios on radio control helicopters are able to generate significant precession roll and yaw torques that roll or yaw the entire model, but it's a huge amount of angular momentum. A TREX 700's aerobatic (idle up) 62 inch | 5 1/6 foot long rotor speed is 2200 rpm, equivalent to rolling at 405.8 mph.

To clarify the situation, the ratio of total weight to rotor weight on the TREX 700 is about 10:1 (12 lbs : 1.2 lbs), similar to a V8F, total weight EUC and me, 225 lbs, weight of motor, wheel, tire 17.5 lbs, 12.8: 1 ratio, less for a lighter rider. For a Sherman with a light rider (173 lbs with gear) total weight about 250 lbs, weight of motor, wheel, tire, ~38.5 lbs, 6.5:1 ratio. Using the Sherman as an example, to get the same relative amount of yaw torque response of an TREX 700, the Sherman would need to be going 260 mph. At 40 mph, the yaw torque effect on the Sherman would be about 1/6.5 that of the TREX 700, at 30 mph, 1/8.67, at 20 mph, 1/13. 

In addition to the issue of angular inertia about the yaw axis of the non-rotating parts of the EUC, and of the rider, any precession related yaw torque is also opposed by friction at the contact patch, which is mostly responding to camber effect yaw due to tilt and tire parameters.

The riders in the EUC racing videos going 30 to 40 mph in turns don't seem to be having issues tilting their EUCs, easily overcoming any angular momentum in the wheels. There's some amount of precession effect, but as I commented before, I don't know if a rider could distinguish between camber effect yaw torque and the much smaller precession related yaw torque based on the riders inputs.

Edited by rcgldr
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6 hours ago, Tawpie said:

I love this topic!

I have learned

It may be the wrong approach to take to figure out how precession works by just reading.

I actually have a bicycle wheel with pegs installed over the axle, one of each side. Those threaded foot pegs are inexpensive, and are used by BMX riders who place their feet on them to do tricks.

I even have zip tied a steel chain around the rim for more effect. But it is not necessary. 

Hold one hand on a peg. Spin the wheel with the other hand. Tilt the axle with your hand holding the peg. You will feel and see precession at work. You can then test torque-free precession and torque-induced precession.

 

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OK. Below are what my observations.

I rode my V12 first. My V12 has a heavy scooter tire mounted on it. At speeds slightly above 40 km/h, my legs can definitely feel gyro effects. But I cannot say, I was able to observe precession induced steering.

My T3 has the stock tire on. CST-1488 16x2.125. This a very light, relatively small tire. At a bit over 40 km/h speeds, I cannot feel appreciable gyro effects.

 

I also took out my bicycle wheel to observe how precession induced steering would look and feel like. For this case, the chain that was wrapped around the rim was removed. The rim has no tire mounted. When the wheel was not spun fast enough, my hands could not feel any gyro effects. And when my hands could not feel any gyro effects, no precession induced steering can be observed or felt whe I tilt the axle. When the wheel is spun fast enough, my hands can feel gyro effects, and when I tilt the axle, I can clearly see and feel precession induced steering. When the tilting of the axle stops, precession induced steering immediately stops. Note also with precession induced steering, the wheel is not only tilted (leaned), but additionally, the wheel also has a yaw twist.

Based on this observation, at this point in time, I am not convinced my T3 traveling at 40 km/h could facilitate appreciable precession induced steering.

As for my V12 traveling at 40 km/h, it is possible that there is some precession induced steering. But I still need to look into it further.

Edited by techyiam
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49 minutes ago, techyiam said:

I also took out my bicycle wheel to observe how precession induced steering would look and feel like. When the wheel is spun fast enough, my hands can feel gyro effects, and when I tilt the axle, I can clearly see and feel precession induced steering.

An experiment to try, but be careful. Spin the wheel then hold both pegs and tilt the wheel left or right a small amount. The wheel should precess about a vertical axis, and it could end up rubbing against one of your arms, so only tilt the wheel in small increments. Once you have determined a safe amount to tilt the spinning wheel, tilt the wheel and see how much force it takes to keep the wheel from precessing about a vertical axis with forwards | backwards force on the pegs. If you can prevent the precession in this manner, does the force it takes to tilt the wheel increase or decrease?

 

Edited by rcgldr
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3 hours ago, techyiam said:

It may be the wrong approach to take to figure out how precession works by just reading.

Always true for me! (concrete learner).

It still fusses with my pea brain why higher angular momentum makes the wheel resist tilting unless the cone induced yaw (which is a continuously applied change in direction) gets converted by precession into a force vector that wants to tilt me back to vertical. That plus cone effect might combine to return a ghost ridden wheel to vertical? (I think the cone effect is predominant for auto-correction, just because the wheel angular momentum is so low)

 

Edited by Tawpie
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56 minutes ago, rcgldr said:

If you can prevent the precession in this manner, does the force it takes to tilt the wheel increase or decrease?

Obviously, the force it takes increases. And I confirmed it.

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3 hours ago, Eucner said:

For a smooth constant tilt angle turn the centrifugal force and wheels tilt moment are in balance. To get the righting force the turning radius needs to be reduced or speed increased.

Right.

3 hours ago, Eucner said:

The cone effect doesn't do either. It is a constant.

The camber effect decreases the radius when the tilt angle increases (which happens when a roll torque is applied).

3 hours ago, Eucner said:

The gyroscopic precession will reduce the turning radius, so it is quite obvious which is working here.

Gyroscopic precession that reduces the turn radius requires a roll torque. And when there is a roll torque also the tilt angle and hence the camber effect increase. So what is obvious to you is not obvious to me.

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29 minutes ago, Eucner said:

Yes, probably not. The gyroscopic precession is weak at low speed. To be sure we should calculate it. What you try to prove? I'm having nothing against the cone effect. It just isn't the only force in the equation.

I don't know that anyone was considering the camber effect to be the only force. Its appealing aspect is that the camber effect can explained the strange phenomenon of a fixed/forced wheel lean angle in curves (the famous Z10 effect) which precession can not, AFAICS.

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2 hours ago, techyiam said:

I rode my V12 first. My V12 has a heavy scooter tire mounted on it. At speeds slightly above 40 km/h, my legs can definitely feel gyro effects.

What do you feel specifically?

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7 hours ago, rcgldr said:

In addition to the issue of angular inertia about the yaw axis of the non-rotating parts of the EUC, and of the rider, any precession related yaw torque is also opposed by friction at the contact patch, which is mostly responding to camber effect yaw due to tilt and tire parameters.

Due to the tire rotation over ground this friction should be minimal at higher speed, don't you think?

When I apply a yaw torque to the tilted stationary wheel, the torque induces rather a circular forward-backward movement than a rotation of the wheel. That is, precession should tend to (momentarily) speed up the wheel in response to a torque in tilt direction.

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35 minutes ago, Mono said:

What do you feel specifically?

By Gyro effects, I mean resistance force opposing my inner lower leg, as I nudge the side of the wheel with my leg. The wheel wiil not lean easily. If I did the exact same thing under the exact same conditions on my T3, it would have leaned with no resistance. As speed increases, the resistance increases.

Since you ride a V8F, you won't be able to feel gyro effects. If you ever get a chance to ride a Sherman, you would notice it in the first turn you make.

Edited by techyiam
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25 minutes ago, techyiam said:

Gyro effects. That means, if I used by inner lower leg to nudge the side of the wheel, the wheel wiil not lean easily.

Were going straight or in a curve?

Did to try a quick procession of left-right nudges?

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