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 Motorcycle Safety
 Physics and the theoretical
 Spring loaded training wheels that exactly cancel moment caused by gravity
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Andrew Dressel
Male Standard Member
244 Posts


Milwaukee, WI
USA

Moto Guzzi

California Special

Posted - 11/11/2013 :  12:16 AM                       Like
Researchers at Cornell added spring loaded training wheels to a bike. The springs can be adjusted from no stiffness to infinite stiffness to provide the lateral behavior of anything from a bike to a trike and everything in between. Most interesting is when springs are adjusted to exactly cancel the tipping moment generated by gravity.

How do you think it handles?

greywolf
Male Moderator
1492 Posts
[Mentor]


Evanston, IL
USA

Suzuki

DL650AL2

Posted - 11/11/2013 :  12:28 AM
That's nuts. A single track vehicle handles the opposite of a wide track vehicle. Giving a vehicle mixed characteristics of both is a nightmare. It reminds me of http://www.ar15.com/forums/t_1_5/15...ottom#bottom
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Andrew Dressel
Male Standard Member
244 Posts


Milwaukee, WI
USA

Moto Guzzi

California Special

Posted - 11/11/2013 :  1:35 AM
quote:
Originally posted by greywolf

That's nuts. A single track vehicle handles the opposite of a wide track vehicle. Giving a vehicle mixed characteristics of both is a nightmare. It reminds me of http://www.ar15.com/forums/t_1_5/15...ottom#bottom



Sure, it's nuts. A famous quotation is that "If we knew what it was we were doing, it would not be called research, would it?"

Anyway, by cancelling the roll torque due to gravity, it offers a glimpse at the role it plays.

Can you predict how it behaves?
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James R. Davis
Male Administrator
17282 Posts
[Mentor]


Houston, TX
USA

Honda

GoldWing 1500

Posted - 11/11/2013 :  9:42 PM Follow poster on Twitter  Join poster on Facebook as Friend  
Okay, I'll take the plunge and risk being called naive ...

I think the training wheels will have no effect while riding in a straight line but as soon as a change of direction occurs those wheels will begin to 'judder' and the bike will be tossed from side to side - very like a tank slapper. That's assuming the adjustment of those training wheels is dynamic.

If they are fixed, then I think any change of direction will lift the rear wheel off the ground and all the weight of the rear of the bike will be borne by the inside training wheel.
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Andrew Dressel
Male Standard Member
244 Posts


Milwaukee, WI
USA

Moto Guzzi

California Special

Posted - 11/11/2013 :  10:44 PM
quote:
Originally posted by James R. Davis

Okay, I'll take the plunge and risk being called naive ...

I think the training wheels will have no effect while riding in a straight line but as soon as a change of direction occurs those wheels will begin to 'judder' and the bike will be tossed from side to side - very like a tank slapper. That's assuming the adjustment of those training wheels is dynamic.

If they are fixed, then I think any change of direction will lift the rear wheel off the ground and all the weight of the rear of the bike will be borne by the inside training wheel.



You are right about riding in a straight line, but the implementation they show doesn't have an oscillation problem. The motion is nice and smooth. Yes, when fixed, the rider could get it up on just two wheels, but the rear wheel track is pretty wide, and they don't get it going fast enough to lift the inside wheel.

For a hint, think about the difference in lean angle between corning on earth and on the moon at the the same forward speed and turn radius. Then extrapolate that to zero g, but still with sufficient friction.
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James R. Davis
Male Administrator
17282 Posts
[Mentor]


Houston, TX
USA

Honda

GoldWing 1500

Posted - 11/12/2013 :  5:56 AM Follow poster on Twitter  Join poster on Facebook as Friend  
I cannot envision what you hinted at.

It is possible that the bike always rides in a 'straight line' - as the front wheel is deviated from straight ahead, the 'virtual contact patch' of the rear moves it that direction, but the bike proceeds in a straight ahead direction.
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scottrnelson
Advanced Member
6886 Posts
[Mentor]


Pleasanton, CA
USA

KTM

990 Adv, XR650L

Posted - 11/12/2013 :  9:11 AM
quote:
Originally posted by Andrew Dressel

For a hint, think about the difference in lean angle between corning on earth and on the moon at the the same forward speed and turn radius.
I don't believe there would be any difference at all if you had the gravity of the moon compared to the earth for a give speed and radius.

You seem to imply that there is a difference. I would love to hear your explanation.
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Andrew Dressel
Male Standard Member
244 Posts


Milwaukee, WI
USA

Moto Guzzi

California Special

Posted - 11/12/2013 :  1:25 PM
quote:
Originally posted by scottrnelson

quote:
Originally posted by Andrew Dressel

For a hint, think about the difference in lean angle between corning on earth and on the moon at the the same forward speed and turn radius.
I don't believe there would be any difference at all if you had the gravity of the moon compared to the earth for a give speed and radius.

You seem to imply that there is a difference. I would love to hear your explanation.



Sure. The expression we use to calculate a lean angle for a given speed and turn radius is theta = atan(v^2 / (r*g)), right? Thus, as g decreases, theta increases.
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scottrnelson
Advanced Member
6886 Posts
[Mentor]


Pleasanton, CA
USA

KTM

990 Adv, XR650L

Posted - 11/12/2013 :  5:00 PM
quote:
Originally posted by Andrew Dressel

Sure. The expression we use to calculate a lean angle for a given speed and turn radius is theta = atan(v^2 / (r*g)), right? Thus, as g decreases, theta increases.

Okay, I see your point. I had never thought about it that way.

So on Jupiter you would be able to take turns very quickly without scraping parts, right?
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Andrew Dressel
Male Standard Member
244 Posts


Milwaukee, WI
USA

Moto Guzzi

California Special

Posted - 11/12/2013 :  7:12 PM
quote:
Originally posted by scottrnelson
Okay, I see your point. I had never thought about it that way.

So on Jupiter you would be able to take turns very quickly without scraping parts, right?



I never thought of it that way either, but it was a fun presentation on the first day here at BMD2013.
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Andrew Dressel
Male Standard Member
244 Posts


Milwaukee, WI
USA

Moto Guzzi

California Special

Posted - 11/14/2013 :  3:35 PM
quote:
Originally posted by James R. Davis

Okay, I'll take the plunge and risk being called naive ...

I think the training wheels will have no effect while riding in a straight line but as soon as a change of direction occurs ...

If they are fixed, then I think any change of direction will lift the rear wheel off the ground and all the weight of the rear of the bike will be borne by the inside training wheel.



It turns out, that you are correct about the fixed wheels, depending on speed of course. It rides just like a trike.

And, they do nothing if they are completely slack. It rides just like a bike.

The idea was to find out what happens in the transition between these two extremes. Might a smooth transition help novices learn how to ride a bike? The answer is a resounding "no".

At the critical point, when the springs are tuned to exactly cancel the roll moment of gravity, the bike cannot be steered. The slightest deviation from straight ahead causes an uncontrolled lean in the opposite direction that can only be corrected by steering back to the straight course.

As the equation for lean angle dictates, as g goes to zero, theta must go to 90 degrees for any turn radius and forward speed.

Another take on it is that bikes have two degrees of freedom, heading and lean angle, but only one control, steer angle. The moment generated by gravity makes it possible to control both degrees of freedom with one actuator by that slick trick called countersteering. Take away gravity, however, and you can only control either heading or lean angle, but not both.

There is a video, but it hasn't been posted online anywhere yet. In it, a rider is shown navigating a short slalom course, first in bike mode, then in trike mode, and finally with gravity canceled. The first two work as expected, but the rider appears completely unable to make the third mode deviate from a straight course at all. I believe what is going on is that the slightest deviation causes it to initiate a 90 degree lean on the opposite direction, which the rider finds disconcerting, and so they steer back to the straight line, which cancels the lean.
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gymnast
Moderator
4263 Posts
[Mentor]


Meridian, Idaho
USA

Harley-Davidson

Sportster Sport

Posted - 11/14/2013 :  4:56 PM
quote:
Originally posted by Andrew Dressel

quote:
Originally posted by scottrnelson
Okay, I see your point. I had never thought about it that way.

So on Jupiter you would be able to take turns very quickly without scraping parts, right?



I never thought of it that way either, but it was a fun presentation on the first day here at BMD2013.



I hope you are enjoying the conference and will pass along anything that you believe will be of interest to members of this forum. Great to see you are on the cutting edge and I as well as others here are looking forward to you having a great career and influence on the advancement of motorcycling.
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greywolf
Male Moderator
1492 Posts
[Mentor]


Evanston, IL
USA

Suzuki

DL650AL2

Posted - 11/14/2013 :  5:54 PM
No surprises there. Like the backwards bike, it's practically impossible to steer.
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Andrew Dressel
Male Standard Member
244 Posts


Milwaukee, WI
USA

Moto Guzzi

California Special

Posted - 11/17/2013 :  12:02 PM
quote:
Originally posted by gymnast
I hope you are enjoying the conference and will pass along anything that you believe will be of interest to members of this forum.



Other interesting things include:

  • Steer-by-wire: enables all sorts of fun things like stability enhancement and making one bike feel like another bike.

  • All-wheel-drive: only looking at efficiency so far.

  • Tilting of narrow track vehicles: there are a variety of ways to accomplish it.

  • Rear-wheel-steer: yes it can be quite ridable and even self-stable, if designed properly.

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