3 ms·

Researchers explain why bicycles balance themselves

18 points by flyingyeti 16y ago

wiredfool 16y ago
I had Ruina as a dynamics prof many years back. Good teacher, Good class. I still remember that he was interested in self walking robots at the time, powered only by gravity and walking down a slight slope.
- kragen 16y ago
  How do those work? With the Jansen linkage?
  - wiredfool 16y ago
    I remember a three legged version, with the inner leg out of phase with the outer two. This is a more refined two legged version, http://www.youtube.com/watch?v=_2pAMe_5VeY http://www.youtube.com/watch?v=_2pAMe_5VeY . Power here is gravity, in the form of a slight slope on the surface it's walking on. The walking form is all from dynamic motion, no electronic control. It looks simpler than a jansen linkage, much more like the physiology of our legs. (and there's a funny story there, Prof Ruina had a limp when he taught the class, because he had implanted studs in the bones of one of his legs so that they could motion capture the bone motion when he walked. Not sure if the limp affected that.)
dmlorenzetti 16y ago
This publicity release mis-advertises what is new here. From the publicity release: Now, a new analysis says the commonly accepted explanations are at least partly wrong. The accepted view: Bicycles are stable because of the gyroscopic effect of the spinning front wheel or because the front wheel "trails" behind the steering axis, or both. From a Wikipedia article (http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics): In 1970, David E. H. Jones published an article in Physics Today showing that gyroscopic effects are not necessary to balance a bicycle. In fact, Jones' article addresses the steering axis question, as well. What appears to be new here is the mathematical analysis. From Jones: I have not yet formalized all these contributions into a mathematical theory of the bicycle...
vlisivka 16y ago
> They built a bicycle with two small wheels, each matched with a counter-rotating disk to eliminate the gyro effects ...to double gyro effects... or I missed something? Two conter-rotating disks will compensate each other, BUT they must be perfectly aligned, is not? In their bicycle, upper disk produces about 2x of gyro effect comparing to lower disk gyro effect, because it moves with about 2x larger amplitude comparing to lower disk at same incline, thus we still have about 2x-1x=1x gyro effect. They should try their system on skates with two tiny blades instead of wheels. PS. Sorry for my English - I am Ukrainian. PPS. System need to spent some energy to restore vertical alignment of inclined body. Thus they need to add small incline to bicycle and then find where motion energy is spent by bicycle to restore vertical alignment. If bicycle will unable to restore vertical alignment then it is not stable.
hoag 15y ago
This is awesome: I have seriously been searching for an explanation on this ever since I was a little kid and my dad bought me my first bike at about 3 years of age and immediately removed the training wheels.

18 points by flyingyeti 16y ago

I had Ruina as a dynamics prof many years back. Good teacher, Good class. I still remember that he was interested in self walking robots at the time, powered only by gravity and walking down a slight slope.

kragen 16y ago
How do those work? With the Jansen linkage?
- wiredfool 16y ago
  I remember a three legged version, with the inner leg out of phase with the outer two. This is a more refined two legged version, http://www.youtube.com/watch?v=_2pAMe_5VeY http://www.youtube.com/watch?v=_2pAMe_5VeY . Power here is gravity, in the form of a slight slope on the surface it's walking on. The walking form is all from dynamic motion, no electronic control. It looks simpler than a jansen linkage, much more like the physiology of our legs. (and there's a funny story there, Prof Ruina had a limp when he taught the class, because he had implanted studs in the bones of one of his legs so that they could motion capture the bone motion when he walked. Not sure if the limp affected that.)

dmlorenzetti 16y ago

This publicity release mis-advertises what is new here. From the publicity release: Now, a new analysis says the commonly accepted explanations are at least partly wrong. The accepted view: Bicycles are stable because of the gyroscopic effect of the spinning front wheel or because the front wheel "trails" behind the steering axis, or both. From a Wikipedia article (http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics): In 1970, David E. H. Jones published an article in Physics Today showing that gyroscopic effects are not necessary to balance a bicycle. In fact, Jones' article addresses the steering axis question, as well. What appears to be new here is the mathematical analysis. From Jones: I have not yet formalized all these contributions into a mathematical theory of the bicycle...

vlisivka 16y ago

> They built a bicycle with two small wheels, each matched with a counter-rotating disk to eliminate the gyro effects ...to double gyro effects... or I missed something? Two conter-rotating disks will compensate each other, BUT they must be perfectly aligned, is not? In their bicycle, upper disk produces about 2x of gyro effect comparing to lower disk gyro effect, because it moves with about 2x larger amplitude comparing to lower disk at same incline, thus we still have about 2x-1x=1x gyro effect. They should try their system on skates with two tiny blades instead of wheels. PS. Sorry for my English - I am Ukrainian. PPS. System need to spent some energy to restore vertical alignment of inclined body. Thus they need to add small incline to bicycle and then find where motion energy is spent by bicycle to restore vertical alignment. If bicycle will unable to restore vertical alignment then it is not stable.

hoag 15y ago

This is awesome: I have seriously been searching for an explanation on this ever since I was a little kid and my dad bought me my first bike at about 3 years of age and immediately removed the training wheels.