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#31
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"The Stability of the Bicycle"
Its all a mater of momentum. The linear momentum of the bike and rider
is far greater than that of the wheel, at any speed. here is an experiment. try pushing someone who is pushing a bike. notice how hard it is. You turn the bike by changing your momentum by leaning. The front wheel is only following your path. John Docherty |
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#32
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"The Stability of the Bicycle"
wow. you've just completely rewritten the world of physics. absolutely
extroardinary. look, take a bike wheel, suspend one end of the axle from a piece of string, then spin it in the normal vertical position. the wheel will appear to "defy gravity" by remaining near vertical with its axis perpendicular to the string. then you will notice that the wheel axis is itself rotating around the string. this is because the reolved resoulution of simple newtonian physics resolves at 90 degrees to the applied force, i.e. the string pulls up against the wheel's center of gravity axis, so the wheel moves at 90, thus rotating. when you tilt a fork of a bike with a rotating wheel in it, there's no reason for the physical world to suddenly distort and suddenly run counter to normal. as has been described by a previous poster, a vehicle ith no rotating components still banks & steers satisfactorily. gyro forces DO NOT make the bike bank. if you don't want to believe me [sic], just dig out that old high school physics footage of a bike being ridden with a counter gyroscopic wheelset. works just fine. jb. |
#33
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"The Stability of the Bicycle"
Their presence is
demonstrable without delving into jargon and mathematical proofs. hmmmm. now you're in the same territory as your new metal fatigue hypothesis. come on jobst, you're the engineer. this is a tech forum. get with the science. drop the conjecture. please. jb. |
#34
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"The Stability of the Bicycle"
jim beam wrote:
wow. you've just completely rewritten the world of physics. absolutely extroardinary. look, take a bike wheel, suspend one end of the axle from a piece of string, then spin it in the normal vertical position. the wheel will appear to "defy gravity" by remaining near vertical with its axis perpendicular to the string. then you will notice that the wheel axis is itself rotating around the string. this is because the reolved resoulution of simple newtonian physics resolves at 90 degrees to the applied force, i.e. the string pulls up against the wheel's center of gravity axis, so the wheel moves at 90, thus rotating. when you tilt a fork of a bike with a rotating wheel in it, there's no reason for the physical world to suddenly distort and suddenly run counter to normal. as has been described by a previous poster, a vehicle ith no rotating components still banks & steers satisfactorily. gyro forces DO NOT make the bike bank. Umm. I really think you need to re-read what he wrote. if you don't want to believe me [sic], just dig out that old high school physics footage of a bike being ridden with a counter gyroscopic wheelset. works just fine. And is reportedly "almost impossible" to ride no-hands, as Jobst has claimed. -- Benjamin Lewis Seeing is deceiving. It's eating that's believing. -- James Thurber |
#35
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"The Stability of the Bicycle"
as Jobst has
claimed. that's proof? |
#36
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"The Stability of the Bicycle"
Simon Brooke 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). 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? There are no "maths", math is an aggregate concept and has no plural... except in GB maybe. I guess you don't have a bicycle with a QR front wheel so you can't perform the simple experiment of turning the wheel at "walking speed" to fell the strong gyroscopic effect caused by tilting the wheel manually to the left and right. Jobst Brandt |
#37
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"The Stability of the Bicycle"
Simon Brooke writes:
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. OK, I have just been out to the bike shed and carried out an empirical experiment; and this is just false. My observations are, when stationary: (i) On rougher surface (grass), greater lean angles are required before a steering effect is noticed as compared to smoother surfaces (tiled floor). (ii) On tyres with a larger contact patch (mountain bike), greater lean angles are required before a steering effect is noticed as compared to smaller contact patch (road bike). (iii) All bikes on all surfaces showed steering effect on lean. (iv) Road bike on tiled floor showed to within the limits of observational measurement as much steering effect on the same amount of lean when stationary as when moving. (v) By contrast, a mountain bike on grass had to be leant to a considerable angle to show any steering effect when stationary, and when the steering effect did occur it occured in jerky movements through considerable angles. From this I conclude that the resistance to steering when stationary is as much due to friction at the contact patch as anything else (and, lets face it, tyres are designed to generate the maximum possible friction at the contact patch). I'm quite prepared to repeat the experiment on camera an post a quicktime movie. But it's a very simple experiment and I'm sure everyone else can repeat it too. No need to belabor what is self evident. We have all parked a bicycle either leaning against a wall or on a kick-stand and seen that the front wheel turns to the side to which the bicycle leans. This is not what steers the bicycle in this exercise. When walking a bicycle, holding it by the saddle, lean angles are trivially small and cause steering by gyroscopic action, the test for which you have apparently not done. Take the wheel out of the bicycle, turn it at "walking speed" and tilt it to the left and right in your hands. You will notice a quick and relatively forceful steering response. It is this force that allows the bicycle to be steered by slight lean angles, the method of riding no-hands and the forces that cause shimmy. If you cannot ride no-hands you'll have to leave it at wheeling the bicycle by the saddle. Jobst Brandt |
#38
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"The Stability of the Bicycle"
Simon Brooke 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. Oh! Tell me how far you rode it riding no-hands and how you wheeled it while walking and holding it by the saddle. 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. Well don't just sit there and fret about it, try it. Take the wheel out and turn it. Jobst Brandt |
#39
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"The Stability of the Bicycle"
Jim Beam writes:
wow. you've just completely rewritten the world of physics. absolutely extroardinary. You'll have to be more explicit. What is it that you find extraordinary and contrary to "the world of physics"? Look, take a bike wheel, suspend one end of the axle from a piece of string, then spin it in the normal vertical position. The wheel will appear to "defy gravity" by remaining near vertical with its axis perpendicular to the string. Then you will notice that the wheel axis is itself rotating around the string. This is because the reolved resoulution of simple newtonian physics resolves at 90 degrees to the applied force, i.e. the string pulls up against the wheel's center of gravity axis, so the wheel moves at 90, thus rotating. In spite of the garbled text, I don't see in what way this contradicts steering a bicycle using these forces, if I deciphered it correctly. By the way, have you performed this experiment or did you only read about it? If you have done this, you'll note that the axle of the wheel remains in a horizontal plane down rotation speed of the wheel below one revolution per second. When you tilt a fork of a bike with a rotating wheel in it, there's no reason for the physical world to suddenly distort and suddenly run counter to normal. What do you mean by this. Can you translate that to plain English? As has been described by a previous poster, a vehicle ith no rotating components still banks & steers satisfactorily. Gyro forces DO NOT make the bike bank. I think you have that backwards, banking (or leaning) the bicycle to one side or the other causes the wheel to turn, not the converse. If you don't want to believe me [sic], just dig out that old high school physics footage of a bike being ridden with a counter gyroscopic wheelset. Works just fine. I'm not familiar with your "footage". Jobst Brandt |
#40
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"The Stability of the Bicycle"
"jim beam" wrote:
Benjamin Lewis: "jim beam" as Jobst has claimed. that's proof? There's a neat piece of selective quoting. What this should read is; old high school physics footage of a bike being ridden with a counter gyroscopic wheelset. works just fine. And is reportedly "almost impossible" to ride no-hands, as Jobst has claimed. I.e., the behaviour of this bike substantiates Jobst's claim. -- David Damerell Kill the tomato! |
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