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Mechanics of turning (how does it actually work?)


kolmog

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I'm new and still figuring things out, and one of the things that I'm struggling with is turning.

I know there are plenty of topics and videos about turning, but I haven't seen one that explains it in terms of it's actual mechanics so I thought it might be interesting, and I would also like to understand whats happening when I'm on the wheel.

The problem is the following: when turning, where does the rotational torque actually come from?

In the case of a body twist turn, it seems to be the following: the wheel on the ground provides enough friction (reverse torque) that you can slowly twist your body in the direction that you want to go. The wheel can stay totally upright. Once the majority of your body weight is facing where you want to go, and with the additional rotational momentum you have gained, you can rotate the wheel despite the friction with the ground.

With a continuous turn this is not the case; you are not twisting your body in order to turn. And from what I have seen, the wheel has to be at an angle. So there are 2 possible things that could contribute to the rotational torque, that I know of:

1. The difference in circumference between the middle of the wheel and the inside of the wheel. Essentially like rolling a bucket on the floor. If this was where the turning force came from, then it would be easier to turn on a wheel with less air pressure (maybe someone experienced can comment?).

0Mp7R.jpg

2. The thing that happens when a coin is rolling at an angle; it rolls in circles. But why does this happen? This page seems to have the answer, but I am not sure I understand it; it seems to be a difference between the forces acting on the front side (going down with gravity) and the back side (going up against gravity) of the wheel. So it depends on rotational momentum; in this case, turning would be easier on an euc with a heavier wheel (again maybe someone can comment). And if the wheel weighed nothing, it would be impossible.

So do these effects in 1 and 2 adequately explain turning on an euc? Is it possible to do a continuous turn while keeping the wheel totally upright? Usually it seems like people are exaggerating the angle of the wheel when turning. Thanks!

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5 hours ago, kolmog said:

So do these effects in 1 and 2 adequately explain turning on an euc?

They do! Basically you do have it all figured out already.

 This was discussed in detail about a month ago, I wish I’d remember the topic title!

 The force that turns a round tire when tilted is called the camber effect. Essentially the tire acts like a rolling cone.

And if I remember the English term correctly, the force that turns a spinning disc is called a gyroscopic precession. This was demonstrated to us in school with a detached bicycle wheel. Pushing the top of a spinning wheel caused it to turn because the precession makes the force act 90• later at the wheel’s circumference.

 Together these two forces keep a long turn alive on an EUC.

 The rider needs to compensate for one’s forward going mass by leaning into the turn depending on the turn’s circumference and speed. Wide tires have a stronger camber effect, so they are held more upright for the same turn.

 There are also forces related to the flexing tire, but I hope someone with a better understanding on them can shed light on how they effect the whole thing.

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The coin example is different than what happens on an EUC. There's no rider on the coin, and the coin is never in a coordinated turn, the inwards torque due to gravity pulling down at the center of mass of the coin and the floor pushing up at the contact point, is not completely countered by the outwards torque from the outwards centrifugal reaction force at the center of mass and the inwards centripetal force at the contact point, so there is always a net inwards torque. The coin responds to this net inwards torque with a 90 degree delay into a steering reaction due to precession, steering it so that it continues rolling in a circle in the idealized case where there's no rolling resistance and the speed is constant.

An EUC has a rider on it, and the angular inertia of the rider opposes any precession related reaction by the wheel. Generally a rider performs a coordinated turn, where the inwards and outwards torques nearly cancel, which also reduces any precession related effects. Instead, camber effect (truncated cone), as explained in the thread linked to by mrelwood explains how tilting an EUC causes it to steer. As also noted in that other thread, a rider can use use yaw impulses to steer an EUC without leaning it, or use a combination of both yaw and tilt inputs. 

 

Edited by rcgldr
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I'm new as well and I really love to learn / talk about the physics behind the technology we are using. Are you posting to get more into the science or trying to improve your ride?  I find that when I stop overthinking about the turns coming up and just look ahead at the path ahead it pulls you automatically.

As a beginner I find it helps when I stay on the paths I already memorized all the turns, bumps, crosswalks and any possible dangers etc. So basically don't force or overthink stuff just go with the flow :)

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16 hours ago, rcgldr said:

An EUC has a rider on it, and the angular inertia of the rider opposes any precession related reaction by the wheel. Generally a rider performs a coordinated turn, where the inwards and outwards torques nearly cancel, which also reduces any precession related effects. Instead, camber effect (truncated cone), as explained in the thread linked to by mrelwood explains how tilting an EUC causes it to steer. As also noted in that other thread, a rider can use use yaw impulses to steer an EUC without leaning it, or use a combination of both yaw and tilt inputs. 

Hm... I would like if there were some easy way to test this, might be interesting.

 

2 hours ago, AeonDrone said:

I'm new as well and I really love to learn / talk about the physics behind the technology we are using. Are you posting to get more into the science or trying to improve your ride?

Having an intuition for the mechanics is a way to learn for me. I think if you know how something is supposed to work that may give you the confidence to execute it correctly. Small turning circles became much easier after learning how it works. Kind of like a learning shortcut.

Another example, not related to turning: if you hit a bump, that is not too big for the wheel to get over, how fast does the wheel react? The resistance from the bump will convert some of the wheel's forward motion into upward motion causing it to slow down from the bottom. It will then tilt forward, and if it is unable to increase the torque quickly to balance itself then the rider will come off the front. My experiences so far tell me that the wheel is reacting very fast, since there doesn't seem to be any compensation required in order to go over small bumps. However, if I knew exactly what was going on then I might try some larger ones.

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4 hours ago, kolmog said:

Hm... I would like if there were some easy way to test this, might be interesting.

This is explained in the thread that mrelwood linked to, but here is a summary.

For normal speeds, tilt steering is the most common. You tilt the EUC with your feet and legs, and it will steer in the direction of tilt due to camber effect. The rider in this video is almost motionless (no body twisting or arm flailing) other than leaning and tilting the EUC. Due to the light rider, speed, turning radius, ... ,  the rider is leaning more than the EUC is tilted most of the time:

https://www.youtube.com/watch?v=-hWMwK3Cfs0

For very low speeds yaw steering is used (the EUC doesn't have to be tilted). You twist upper body and|or arms in the opposite direction you want to steer the EUC. Extreme example of this while nearly stopped.

https://www.youtube.com/watch?v=ro3o8U9uZeU&t=57s

You can use a combination of tilt steering and mild yaw steering (using lower legs to steer without much upper body movement) at moderate speeds. Tilt and|or yaw steering can be used to regain balance if a rider starts to fall to either side. Steer into the direction of fall.

The third method is body twisting. The rider twists the upper body inwards then uses the momentum for some yaw steer effect, and is normally combined with tilt steering. This is done when balanced to setup a turn, and would not be good for fall recovery, because it delays the steering response and|or increases the lean of the fall before actual inwards steering occurs. This is the first type of turn shown in this video, but you can clearly see he tilts the EUC in addition to body twisting.

https://www.youtube.com/watch?v=xARhopySrtk

In my case, I first used yaw steering at low speed in a tennis court. After moving to a location with a long straight section, I increased speed to around 6 to 8 mph, where my V8F became more stable, focused on leaning forwards | backwards for speed control, and tried tilting the EUC left and right by small amounts and slowly to see how it would respond, since I didn't know how it was going to respond. Once I realized how it would respond, my tilt steering quickly evolved into a left and right weave pattern. I then worked on using tilt steering for turns and balance. Currently, I consciously use tilt steering for balance, but this should eventually evolve into a reflexive reaction. If needed, I still use some yaw steering for balance at lower speeds.

 

Edited by rcgldr
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45 minutes ago, kolmog said:

Having an intuition for the mechanics is a way to learn for me.

For me as well, which is one of the reasons I like to participate in discussions like this.

45 minutes ago, kolmog said:

Small turning circles became much easier after learning how it works.

For small continuous circles, camber effect is the main contributor. Allow the wheel to tilt between your legs and you can be in for a very small circle.

Turn your shoulders to the direction of the turn at the right time and it will tighten even further. The way I do this probably introduces continuity of mass, as I’m taking speed for a spin from the friction of the straight going tire before the turn. It isn’t the only part though, since upper body pointing to the outside turn makes the turn harder, even when stationary. I don’t know what that’s about.

45 minutes ago, kolmog said:

if you hit a bump, that is not too big for the wheel to get over, how fast does the wheel react?

I think “extremely” might be the most precise answer you can get for this…

I think someone once mentioned that the processor in the EUC runs at 800Hz. So depending on the programming and the riding mode being used, it could “react” up to 800 times per second. But one would have to know much more about self-balancing programming in general to answer this any better.

 In practice, the harder the riding mode being used is, the less the wheel allows the pedals to tilt before compensating for the tilt. That makes it respond faster, and it doesn’t feel as if the wheel got stuck behind the obstacle.

 But speed is not everything here. If you don’t lighten your load at all, the burden to the wheel is multiplied by about three (a wild guess), and the wheel must ramp up the power much much more. If you preload for a slight jump and keep your knees soft, the wheel can climb with much less resistance.

 There are many off-roading EUC videos in YT, mine included. They will give you some idea about the size of the obstacles you can overcome using a suitable technique. 

 

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Follow up on tilt steering | camber effect. Unlike a motorcycle or aircraft where bank angle and speed determine the turning radius, tilt steering | camber effect is a bit more complicated, because lateral load due to a high g turn will reduce camber effect. For example, a low speed, low g turn with the rider nearly vertical and the pedals nearly scraping will result in a fairly tight turn, but a high speed, high g turn with the rider leaning quite a bit (like EUC racing), may also have the pedals nearly scraping while the turn radius is large. Another example is a lighter rider making a moderate turn at moderate speed, the rider is leaning more than the EUC is tilted.

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