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#21
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"The Stability of the Bicycle"
Peter Rathman writes:
Take the wheel out, spin it in you hands and try to tilt it to the left or right and note the force of the steering action. This should convince you of its effect. please explain. gyro reaction is _90 degrees to the applied force_. i.e. my front wheel, spinning "forwards" tries to tilt top rightwards when turned to the left. you seem to be implying that gyro recation is responsible for banking the bike to the left when steered left. No, when you wheel the bike along holding onto the seat you steer by banking the bike and the turn is a reaction to the bank. Banking the bike to the left will tend to initiate a turn to the left. But the gyroscopic force is quite small when the wheel is spun at only walking speed and the geometry of the bike also results in the wheel turning left in response to a left bank (even when the wheel isn't rotating). I'd have to try this with a counter-rotating second front wheel (like on URB I) before concluding which is the dominant effect. That is why I suggest the spinning wheel in hand experiment. The steering forces are not small and are sufficient at casual walking speed to steer the bicycle. That the bicycle does not steer when stationary shows that effect as well. TO make the bicycle steer merely from rake and trail takes a large lean angle and does not accomplish the same effect. You don't need any esoteric URB's to test this with your own mount although this may not sound as scientifically complex, it demonstrates the effects strikingly. Jobst Brandt |
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#22
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"The Stability of the Bicycle"
anonymous writes:
Take the wheel out, spin it in you hands and try to tilt it to the left or right and note the force of the steering action. This should convince you of its effect. You don't need to solve differential equations. OK, but envision a system without any rotating elements. Substitute a runner or blade shaped essentially the same as the bottom of a wheel and substitute sliding for rolling. Such a device would still have a turning capability without the existence of any gyroscopic effect. You don't have to go to other devices to see that when the wheel is not rotating the self steering does not work. For it to work on a non rotating wheel, the bicycle must be leaned significantly for front wheel trail to have any effect. Don't! There is more to be gained by intelligent observation of natural phenomena. You mean it's OK to be able to "feel" something even if you can't prove it exists mathematically? You don't have to call it "feel". We are talking about physical effects that either do or do not occur. Their presence is demonstrable without delving into jargon and mathematical proofs. Jobst Brandt |
#23
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"The Stability of the Bicycle"
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#24
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"The Stability of the Bicycle"
Peter wrote:
wrote: TO make the bicycle steer merely from rake and trail takes a large lean angle and does not accomplish the same effect. You don't need any esoteric URB's to test this with your own mount although this may not sound as scientifically complex, it demonstrates the effects strikingly. My observations are that either effect could explain the ability to steer a bike by making it lean by small amounts while walking so distinguishing between them would require either constructing a frame/fork with a different rake/trail geometry to eliminate one effect or canceling the gyroscopic force to eliminate the other. May I suggest an experiment? The second gyro wheel is a bit difficult to set up, although it could probably be done with a long solid axle, a BMX axle peg, and a small second wheel. However changing the steering geometry should be easier for the pushing-the-bike experiment. For extra trail, one can reverse the forks. For the negative trail setup (extra rake), one does not need a setup robust enough to ride, just to push. An extra front hub clamped in the forks and a couple of pieces of sheet metal to extend the rake forward could do it. For god's sake don't try to ride it though. |
#25
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"The Stability of the Bicycle"
Peter writes:
jim beam wrote: Take the wheel out, spin it in you hands and try to tilt it to the left or right and note the force of the steering action. This should convince you of its effect. please explain. gyro reaction is _90 degrees to the applied force_. i.e. my front wheel, spinning "forwards" tries to tilt top rightwards when turned to the left. you seem to be implying that gyro recation is responsible for banking the bike to the left when steered left. No, when you wheel the bike along holding onto the seat you steer by banking the bike and the turn is a reaction to the bank. Banking the bike to the left will tend to initiate a turn to the left. But the gyroscopic force is quite small when the wheel is spun at only walking speed and the geometry of the bike also results in the wheel turning left in response to a left bank (even when the wheel isn't rotating). Well, just so. I agree that you can get strong gyroscopic effects with a fast rotating wheel, but I'm completely unpersuaded that they are significant at walking speed. So, again, has anyone done the maths? -- (Simon Brooke) http://www.jasmine.org.uk/~simon/ [ This .sig intentionally left blank ] |
#27
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"The Stability of the Bicycle"
"Benjamin Weiner" wrote in message news:3f8267c7$1@darkstar... Peter wrote: wrote: TO make the bicycle steer merely from rake and trail takes a large lean angle and does not accomplish the same effect. You don't need any esoteric URB's to test this with your own mount although this may not sound as scientifically complex, it demonstrates the effects strikingly. My observations are that either effect could explain the ability to steer a bike by making it lean by small amounts while walking so distinguishing between them would require either constructing a frame/fork with a different rake/trail geometry to eliminate one effect or canceling the gyroscopic force to eliminate the other. May I suggest an experiment? The second gyro wheel is a bit difficult to set up, Also, you could get yourself a 1Kg heavier wheel with some lead weights and some duct tape. |
#28
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"The Stability of the Bicycle"
wrote in message ... Jim Beam writes: Take the wheel out, spin it in you hands and try to tilt it to the left or right and note the force of the steering action. This should convince you of its effect. please explain. gyro reaction is _90 degrees to the applied force_. i.e. my front wheel, spinning "forwards" tries to tilt top rightwards when turned to the left. you seem to be implying that gyro recation is responsible for banking the bike to the left when steered left. Not at all. I suggest that the wheel spinning forward steers to the left when tilted to the left and to the right when tilted to the right. I wouldn't disagree with the above. This is the means by which the bicycle steers when walking the bike while held by the saddle and also what enables it to be ridden no-hands. What is the relative contribution of the different effects - ie to what degree is the above more important than the effects of rake and trail - at different speeds and with the addition of the rider to the whole system. |
#29
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"The Stability of the Bicycle"
"W K" writes:
What is the relative contribution of the different effects - ie to what degree is the above more important than the effects of rake and trail - at different speeds and with the addition of the rider to the whole system. As a child I rode one winter a bicycle which had a normal rear wheel but had part of an old ski bolted onto the front forks in place of the front wheel. It was good fun to use and I don't remember it handling noticably differently from a normal bike. This is a long time ago and I could be wrong, but again it's easy enough to verify. This isn't to deny that gyroscopic effects play some part, nor that the influence of gyroscopic effects increases with speed; but without some maths I'm skeptical about their being significant as compared to lean. -- (Simon Brooke) http://www.jasmine.org.uk/~simon/ ;; how did we conclude that a ****ing cartoon mouse is deserving ;; of 90+ years of protection, but a cure for cancer, only 14? -- user 'Tackhead', in /. discussion of copyright law, 22/05/02 |
#30
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"The Stability of the Bicycle"
"W K" wrote in message ...
wrote in message ... Jim Beam writes: Take the wheel out, spin it in you hands and try to tilt it to the left or right and note the force of the steering action. This should convince you of its effect. please explain. gyro reaction is _90 degrees to the applied force_. i.e. my front wheel, spinning "forwards" tries to tilt top rightwards when turned to the left. you seem to be implying that gyro recation is responsible for banking the bike to the left when steered left. Not at all. I suggest that the wheel spinning forward steers to the left when tilted to the left and to the right when tilted to the right. I wouldn't disagree with the above. This is the means by which the bicycle steers when walking the bike while held by the saddle and also what enables it to be ridden no-hands. What is the relative contribution of the different effects - ie to what degree is the above more important than the effects of rake and trail - at different speeds and with the addition of the rider to the whole system. The mass imbalance is a constant for a given bicycle and the speed at which it will impart steering action is dependent on the lean angle and is easily observable with a stationary bicycle. Gyroscopic precession is dependent on rotation rate of the wheel, the faster the wheel rotates the higher the torque required to lean the wheel for a give rate of precession. At walking speed (1/2 rev/sec) the difference in torque between leaning this and a stationary wheel will be the amount of torque that causes the wheel to turn (precess). It will be small and likely doesn't even overcome the trail effect of keeping the wheel pointed straight ahead. Rider weight adds more tire scrub effects which are small but riding no hands at low speeds is almost impossible due to insufficient gyroscopic forces. It's not until the bicycle is going ~15mph does no hands riding become feasible for the ordinary rider. Gyroscopic forces being large enough to impart adequate self steering. Phil Holman |
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