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#1
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Gyroscopic forces revisited
Hi All,
A while ago there was a thread discussing no-handed riding and the role gyroscopic forces play in bike turning. I hypothesized that gyroscopic forces were not that important, and several things were pointed out to me that almost convinced me. A good dose of insomnia allowed me to think about this for several hours and I am now convinced that gyroscopic forces are virtually irrelevant for riding bikes, hands or no-hands. It was postulated that a clown-bike with tiny wheel would be difficult to ride no hands due to the small gyroscopic forces. Since I don't have a clown-bike to play with, this remains a mystery. But I have observed little kids riding small wheel (10") bikes at below walking pace. I have also spun some 12" wheels in my hand a various speeds to feel what sort of gyroscopic forces are there. Not much. A little kid with a sense of balance not as developed as an adult can ride one of these bikes. I do not believe a kid could keep one of these bikes upright by manual correction alone. These small bikes are stable by themselves, and since the gyroscopic forces are so low, there must be something else at work here. This isn't proof or anything, this is just what got me thinking. I finally pulled out a big plywood board (much to the chagrin of my wife who imagines there are myriad things I could be better spending my time on) and propped it up at an angle and put a bike on it to simulate what happens when a bike is in a turn. It was suggested that in a turn a pendulm hung from the top-tube would hang parallel to the seat tube. When riding no hands in a constant radius turn, this cannot be the case, and I suspect that it is not the case with hands on the bars either. Experiments with my plywood board show that when force is applied straight down through the bike the steering remains straight no matter what the angle of the board (simulated angle of lean). In a turn, the steering cannot be straight, otherwise it wouldn't be called a turn, it would be called a crash. So in a turn (a no-handed one in particular) something has to be holding the steering at a non-straight angle. The only thing it can be is that the center of mass is moved to the side of the plane that is the centerline of the bike. This makes the steering flop into the turn. The combined force of gravity and the acceleration of the turn act from the center of mass through the contact patches of the tires. Since the center of mass is not in the plane of the bike's centerline, this means that the combined force is not parallel to the seat tube and thus a pendulum hanging from the top- tube could not be parallel with the seat tube. Riding with hands on the bars I suspect is the same. But a rider could force the bike to be in the same plane, but then they would need to hold the steering at the proper angle manually. This would no doubt require quite a bit of skill, and I believe in practice to be virtually impossible. But perhaps it is just this skill which separates the good from the great. So what does all that mean? It means that "flop" from an off-center center of mass is what makes a bike turn, and thus while gyroscopic forces make help the initial turn of the steering due to induced lean, it is an unnecessary component that is ultimately irrelevant to turing a bike. The whole COM argument was brought about by thinking about how a radio- controlled motorcycle I used to have woked. Joseph |
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#2
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Gyroscopic forces revisited
Joseph Santaniello writes:
A while ago there was a thread discussing no-handed riding and the role gyroscopic forces play in bike turning. I hypothesized that gyroscopic forces were not that important, and several things were pointed out to me that almost convinced me. A good dose of insomnia allowed me to think about this for several hours and I am now convinced that gyroscopic forces are virtually irrelevant for riding bikes, hands or no-hands. It was postulated that a clown-bike with tiny wheel would be difficult to ride no hands due to the small gyroscopic forces. Since I don't have a clown-bike to play with, this remains a mystery. But I have observed little kids riding small wheel (10") bikes at below walking pace. I have also spun some 12" wheels in my hand a various speeds to feel what sort of gyroscopic forces are there. Not much. A little kid with a sense of balance not as developed as an adult can ride one of these bikes. I do not believe a kid could keep one of these bikes upright by manual correction alone. These small bikes are stable by themselves, and since the gyroscopic forces are so low, there must be something else at work here. This isn't proof or anything, this is just what got me thinking. You should have seen the demo at InterBike where an engineer built a front wheel with a forward rotating flywheel (brass disk) between the spokes driven by a small motor at about the speed you expect from a 27" wheel at 10-15mph. He rode this bicycle no-hands at below 2mph, steady as a rock, up and down the isles. Without the flywheel turning independently, the bicycle was as difficult to ride no-hands as any other bicycle with wheels that size. I finally pulled out a big plywood board (much to the chagrin of my wife who imagines there are myriad things I could be better spending my time on) and propped it up at an angle and put a bike on it to simulate what happens when a bike is in a turn. It was suggested that in a turn a pendulum hung from the top-tube would hang parallel to the seat tube. When riding no hands in a constant radius turn, this cannot be the case, and I suspect that it is not the case with hands on the bars either. Experiments with my plywood board show that when force is applied straight down through the bike the steering remains straight no matter what the angle of the board (simulated angle of lean). In a turn, the steering cannot be straight, otherwise it wouldn't be called a turn, it would be called a crash. So in a turn (a no-handed one in particular) something has to be holding the steering at a non-straight angle. The only thing it can be is that the center of mass is moved to the side of the plane that is the centerline of the bike. This makes the steering flop into the turn. The combined force of gravity and the acceleration of the turn act from the center of mass through the contact patches of the tires. Since the center of mass is not in the plane of the bike's centerline, this means that the combined force is not parallel to the seat tube and thus a pendulum hanging from the top- tube could not be parallel with the seat tube. Riding with hands on the bars I suspect is the same. But a rider could force the bike to be in the same plane, but then they would need to hold the steering at the proper angle manually. This would no doubt require quite a bit of skill, and I believe in practice to be virtually impossible. But perhaps it is just this skill which separates the good from the great. Please discover why one should use paragraphs. You must have come across this in school. So what does all that mean? It means that "flop" from an off-center center of mass is what makes a bike turn, and thus while gyroscopic forces make help the initial turn of the steering due to induced lean, it is an unnecessary component that is ultimately irrelevant to turning a bike. The whole COM argument was brought about by thinking about how a radio controlled motorcycle I used to have worked. I think your research came up with the wrong result. An easily repeatable exercise of coasting down a smooth road at more than 20mph riding no-hands, is to shake one knee from side to side while resting the other one against the top tube for stability. I think there is where you will see the effect the best. In addition, shimmy on a bicycle cannot occur without gyroscopic forces of the front wheel. Jobst Brandt |
#3
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Gyroscopic forces revisited
How about a wheel on it's own? If you roll a wheel and it leans over
it turns in that direction. The reason is that the contact patch of a leaning tyre is parallel to the ground and so at an angle to the wheel's axle so the wheel acts as a rolling cone and turns into the corner (which maintains it's balance). I'm pretty sure that's the main steering force involved in no-handed riding. (I seem to remember reading about someone testing this on a motorbike and finding that on a prolonged corners the handlebars are actually turned slightly outward instead of inward as you;d expect. I think that was due to rake/trail but I don;t have time to think about that right now |
#4
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Gyroscopic forces revisited
On Oct 23, 8:54 pm, wrote:
Joseph Santaniello writes: A while ago there was a thread discussing no-handed riding and the role gyroscopic forces play in bike turning. I hypothesized that gyroscopic forces were not that important, and several things were pointed out to me that almost convinced me. A good dose of insomnia allowed me to think about this for several hours and I am now convinced that gyroscopic forces are virtually irrelevant for riding bikes, hands or no-hands. It was postulated that a clown-bike with tiny wheel would be difficult to ride no hands due to the small gyroscopic forces. Since I don't have a clown-bike to play with, this remains a mystery. But I have observed little kids riding small wheel (10") bikes at below walking pace. I have also spun some 12" wheels in my hand a various speeds to feel what sort of gyroscopic forces are there. Not much. A little kid with a sense of balance not as developed as an adult can ride one of these bikes. I do not believe a kid could keep one of these bikes upright by manual correction alone. These small bikes are stable by themselves, and since the gyroscopic forces are so low, there must be something else at work here. This isn't proof or anything, this is just what got me thinking. You should have seen the demo at InterBike where an engineer built a front wheel with a forward rotating flywheel (brass disk) between the spokes driven by a small motor at about the speed you expect from a 27" wheel at 10-15mph. He rode this bicycle no-hands at below 2mph, steady as a rock, up and down the isles. Without the flywheel turning independently, the bicycle was as difficult to ride no-hands as any other bicycle with wheels that size. That sounds like fun! That seems to indicate that the gyroscopic forces counter the "flop" tendency and keep a bike from turing too much. I wonder if his gizmo would make a chopper bike rideable no hands... I finally pulled out a big plywood board (much to the chagrin of my wife who imagines there are myriad things I could be better spending my time on) and propped it up at an angle and put a bike on it to simulate what happens when a bike is in a turn. It was suggested that in a turn a pendulum hung from the top-tube would hang parallel to the seat tube. When riding no hands in a constant radius turn, this cannot be the case, and I suspect that it is not the case with hands on the bars either. Experiments with my plywood board show that when force is applied straight down through the bike the steering remains straight no matter what the angle of the board (simulated angle of lean). In a turn, the steering cannot be straight, otherwise it wouldn't be called a turn, it would be called a crash. So in a turn (a no-handed one in particular) something has to be holding the steering at a non-straight angle. The only thing it can be is that the center of mass is moved to the side of the plane that is the centerline of the bike. This makes the steering flop into the turn. The combined force of gravity and the acceleration of the turn act from the center of mass through the contact patches of the tires. Since the center of mass is not in the plane of the bike's centerline, this means that the combined force is not parallel to the seat tube and thus a pendulum hanging from the top- tube could not be parallel with the seat tube. Riding with hands on the bars I suspect is the same. But a rider could force the bike to be in the same plane, but then they would need to hold the steering at the proper angle manually. This would no doubt require quite a bit of skill, and I believe in practice to be virtually impossible. But perhaps it is just this skill which separates the good from the great. Please discover why one should use paragraphs. You must have come across this in school. Who says I went to school? Ok, I'll try. ;-) So what does all that mean? It means that "flop" from an off-center center of mass is what makes a bike turn, and thus while gyroscopic forces make help the initial turn of the steering due to induced lean, it is an unnecessary component that is ultimately irrelevant to turning a bike. The whole COM argument was brought about by thinking about how a radio controlled motorcycle I used to have worked. I think your research came up with the wrong result. An easily repeatable exercise of coasting down a smooth road at more than 20mph riding no-hands, is to shake one knee from side to side while resting the other one against the top tube for stability. I think there is where you will see the effect the best. In addition, shimmy on a bicycle cannot occur without gyroscopic forces of the front wheel. I did that very same exercise today on my ride while I was polishing my theory. I don't argue that gyroscopic forces do not turn the steering from leaning the bike. I argue that the steering would turn anyway even if the gyroscopic forces were not there, and that the same force that would do this turning is the force that holds a bike with no hands in a constant arc turn. Joseph |
#5
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Gyroscopic forces revisited
wrote in message ps.com... It was postulated that a clown-bike with tiny wheel would be difficult to ride no hands due to the small gyroscopic forces. Joseph http://www.youtube.com/watch?v=uRvwRgs_ZXE -tom |
#6
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Gyroscopic forces revisited
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#7
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Gyroscopic forces revisited
Jon_C wrote:
How about a wheel on it's own? If you roll a wheel and it leans over it turns in that direction. The reason is that the contact patch of a leaning tyre is parallel to the ground and so at an angle to the wheel's axle so the wheel acts as a rolling cone and turns into the corner (which maintains it's balance). I'm pretty sure that's the main steering force involved in no-handed riding. (I seem to remember reading about someone testing this on a motorbike and finding that on a prolonged corners the handlebars are actually turned slightly outward instead of inward as you;d expect. I think that was due to rake/trail but I don;t have time to think about that right now David Jones' paper titled 'unrideable bicycle' discusses all that. I could not find a link (mine's paper) but a search shows 15+ sites with identical phrasing, entertaining for plagiarism buffs. -- Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971 |
#8
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Gyroscopic forces revisited
On Oct 23, 11:25 am, "
wrote: Hi All, A while ago there was a thread discussing no-handed riding and the role gyroscopic forces play in bike turning. I hypothesized that gyroscopic forces were not that important, and several things were pointed out to me that almost convinced me. A good dose of insomnia allowed me to think about this for several hours and I am now convinced that gyroscopic forces are virtually irrelevant for riding bikes, hands or no-hands. .... So what does all that mean? It means that "flop" from an off-center center of mass is what makes a bike turn, and thus while gyroscopic forces make help the initial turn of the steering due to induced lean, it is an unnecessary component that is ultimately irrelevant to turing a bike. I don't think your experiment tested what you think it tested. First, gyro inertia experiments were done in a controlled way by David Jones many years ago. Andrew Muzi alluded to this. You must read the article at http://www.phys.lsu.edu/faculty/gonz...9no9p51_56.pdf He found that the zero-gyro-inertia front wheel (URB 1) was very difficult to ride no-hands. Leaning the bike is how you turn at high speed. Go through a turn at high speed and you'll see that the front wheel is nearly straight. A bit of countersteer initiates the lean and the turn. I'm not sure I'd call this a gyroscopic force, because the flop comes from the steering geometry (fork trail), not from the gyro force on the wheel. As evidence, I don't think you lean the bike at a different angle with a heavy tire on the front wheel, even though that increases the moment of inertia a lot. Of course, you still lean the bike at low speed, but the allowable turn of the front wheel is much greater. When riding no hands, I believe the gyro inertia of the front wheel helps stabilize the front against excessive flop, and this is why it is more difficult to ride no-hands at low speed. So the gyro inertia doesn't help you turn. It helps you not turn. Ben |
#9
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Gyroscopic forces revisited
On Oct 23, 9:41 pm, "Tom Nakashima" wrote:
wrote in message ps.com... It was postulated that a clown-bike with tiny wheel would be difficult to ride no hands due to the small gyroscopic forces. Joseph http://www.youtube.com/watch?v=uRvwRgs_ZXE -tom Do you think this robot being able to ride a bike at super slow speeds with obviously entirely manual steering correction is evidence that a clown bike is difficult to ride no hands, or not so difficult? Joseph |
#10
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Gyroscopic forces revisited
wrote in message ups.com... On Oct 23, 9:41 pm, "Tom Nakashima" wrote: wrote in message ps.com... It was postulated that a clown-bike with tiny wheel would be difficult to ride no hands due to the small gyroscopic forces. Joseph http://www.youtube.com/watch?v=uRvwRgs_ZXE -tom Do you think this robot being able to ride a bike at super slow speeds with obviously entirely manual steering correction is evidence that a clown bike is difficult to ride no hands, or not so difficult? Joseph The hardest part the designers had to deal with robot riding the bike is balance. The engineers installed a gyro sensor that detects angular velocity and inclination, then transmit the data to a computer that adjust the robot's balance. Someone tried to ride a clown's bike with mini wheels and published an article in one of the bicycle magazines. Said they had a hard time keeping their balance. I believe it was a contest to see if anyone could ride it a 100 ft. without putting their foot down. Nobody was able to do it. -tom |
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