Why does an unmanned bicycle stay upright (for a while) when you give it a shove? Researchers from the United States and the Netherlands designed a riderless bicycle that shows that the various mechanisms scientists have long believed to be responsible for keeping bikes upright are actually not necessary.
On a typical bicycle, the front wheel touches ground slightly behind the steering axis (imagine a line extending down from the front forks). This construction is responsible for the "caster effect," in which the bike centers itself not unlike a wheel on a shopping cart. The other effect that was thought to be crucial to bicycle balance is called gyroscopic precession: if a moving bike tilts one way or the other, it will just steer in that direction, thanks to the forward-spinning wheel.
Andy Ruina of Cornell University and his team built a scooter-esque bicycle whose front wheel is in front of the steering axis and whose front and back wheels connect to duplicate wheels that spin in the opposite direction. This construction cancels out both the caster effect and gyroscopic precession. But when they gave it a push, it behaved like any other bike, staying upright almost until all forward motion stopped. Here's a video via Wired showing the bike:
This study shows that what really keeps a bike upright is odd mass distribution: lower in front and higher in the back. If a fall is imminent, the front tries to fall faster than the back. But, since they're connected, this just causes the bicycle to steer into the fall, effectively pulling it out of danger.
This discovery could open up many new possibilities for bicycle design, as engineers would no longer have to design around the caster effect and gyroscopic precession.
so now we can put this into robotic motorcycles
aka the driverless motorcycle soon to be developed by google :D
or skynet...whatever >.>
Not sure I'm buying what they're selling.
The old fashioned high wheel bikes certainly didn't have a lower front.
Then there's this video
I'm not sure that there counter rotating wheels are doing everything that they are postulating.
Agreed Ford.. 2 spinning wheels both oriented vertically are still going to provide vertical gryoscopic action. Since the gyroscopic force of one object is not relative to the gyroscopic force of another object, even if these objects are touching and linked via the same support. The force is cumulative. Take off those extra wheels and lets see how long it lasts.
And as far as the front wheel needing to be behind the steering axis is bogus, motorcyclists have been putting wheels in front of this axis for years and years, just check out any springer front end or those bikes with a heavy rake. The tire is mounted so that the tire touches in front of the steering axis and yet no problems exist there. It's an interesting experiment none the less, but I think more research needs to be put into this before they can just toss out results left and right.
Yeah, I'm not sure this dictates news worthiness. I had an RC Motorcycle that could do the same thing, 30 years ago.
And I'm sure that all you old timers out there remember the old Evel Knievel motorcycles with the hand crank launchers that also did the exact same thing.
If they really wanted to eliminate the gyroscopic forces, they should've removed the wheels entirely and put the thing on ice skates, then see how the weight distribution plays out. You'd think researchers from the Netherlands would have thought of that.
"odd mass distribution"
Well now. Whoda thunkit?
Another of "these" experiments. Ones where supposed scientists think that a counter-rotating wheel somehow cancels out the centrifugal force of the forward rotating wheel instead of simply adding to it as it does in reality.
HBillyRufus, that was the smartest idea I've seen yet to test this. And in all likelyhood, a skate bike without any form of centrifugal force would just fall down. It would be a great way to get rid of these time waster experiments at least.
If you are interested in details about the TMS (two mass skate) bicycle
and what it is about, all you could want to know, and more, is here:
google ruina bicycle
take the top hit and then look for the paper about stability and gyroscopes.
As best I know, no-one who has looked in any detail has any criticism of
You can look at videos and pics on that www site.
Aside: counter-spinning gyros DO cancel. It's perhaps counter-intuititive,
but its part of the strange way that gyroscopes work.
Incorrect. Counter-rotating gyros do not cancel each other out in any way but torque. Take a plane with counter-rotating engines for example. That eliminates gyro drift which is simply due to the gyro torque. While it eliminates that, the resistance to movement of the axis of the whole system is increased and it becomes even more stable than if it only had a single engine spinning one way. In essence, their effects stack because there is no means of getting rid of their rotational forces. Total cancellation is fiction and nonscience.