Topic: Gyroscopic Precession

[GroovieGhoulie]

I tend to think that Gyroscopic Precession is a real phenomenon, but I was reading an article about the guy who designed the front brakes of a bike to spin backwards to offset the gyro effect of the wheels.  He said a "soundbite" that got me thinking.  He said that Gyroscopic Precession was a bunch of bunk and that a bike staying up and stable was purely a matter of balance.  He said that "Ice skates don't have wheels acting as big gyroscopes and they stay upright when moving.  It's all about balance".

Any thoughts on this?  What about his point of ice skates and gyroscopes?  Is he on to something or full of it?

[number13]

He is full of it.
You weren't reading one of those flat eath type websites, were you?

He said that "Ice skates don't have wheels acting as big gyroscopes and they stay upright when moving.

Specious comparison.
Ice skates don't stay upright without a skater wearing them, so that is all the balance of the skater.
If you were to get your bike in motion, without a rider, you would find it will stay upright
as long as it is moving at a high enough speed. That would be your gyroscopic force at work.

[merc2dogs]

 in a way I tend to agree with him.

 I think the gyroscopic forces may contribute, but isn't all of it, not even a great part.

Ken.

 
 

[johnny-from-bel]

 in a way I tend to agree with him.

 I think the gyroscopic forces may contribute, but isn't all of it, not even a great part.

Ken.

 
 

ever tried to tilt a fast sping weel. Its a favourite experiment in any science museum.

The giroscopic effect is very important at high speeds.
2nd is the angle of the ballhead that will stear the frontweel in the direction of the tilt of the bike.

If it is all balance ; ever tried to balance the bike while standing still ?

[merc2dogs]

ever tried to tilt a fast sping weel. Its a favourite experiment in any science museum.

The giroscopic effect is very important at high speeds.
2nd is the angle of the ballhead that will stear the frontweel in the direction of the tilt of the bike.

If it is all balance ; ever tried to balance the bike while standing still ?

 yeah, I have experimented, that's why I say it may contribute, but it's not all of it, or even a large chunk of it.

I weigh 145, my bike weighs 18, that's 163lbs force that the wheels would have to provide to hold the bike upright, roughly 80lbs per. 

it does not take 80lbs of force to change the orientation of a 27 inch bicycle wheel at 250 rpm, which is the speed that it turns at 20mph.
 
  at the equivelent rpm of 10 mph, there is so little effort required that it can have no bearing on the balance.
 consider that a bikcycle is perfectly rideable at less than 5mph, and that at 10mph the rim requires very little more effort than when stationary to turn, and the only conclusion available is that gyroscopic forces can't contribute a great deal to the overall balance issue.
 
 A gyroscope has no effect on forces apllied in line with the axle, example, hold a bicycle rim out in front of you, have someone spin it up to a comfortable speed, then without changing the position of your arms relative to your body, turn around in place, no extra effort is required.  Extra effort IS required if you draw your right arm in and left arme out, ( rim will almmost describe a "S" pivoting on the axle)
 a bicycle applies the forces in a line with the axle, most similarly to turning in place, not like in pivioting the axle, even in turning the axle is away from the actual pivot center point (rake trail)

  consider, if the wheels provide full 'balance' by gyroscopic principles, how much effort should it require to turn the handlebars?
 the forces on steering are applied in the same directions as on maintaining balance, so when turning it -should- require as much effort to turn, as each wheel is providing in balance, on a 500lbs 750 honda with a 200lbs rider, it does not require 350lbs steering effort.

ken.

[333]

Interesting that a ice skating reference was used.  Certainly gyroscopic forces are in play as a skater performs a spin or a rotating jump.  And I used to know a guy that could balance a bicycle standing still, but not for more than 30 seconds or so.

[number13]

it does not take 80lbs of force to change the orientation of a 27 inch bicycle wheel at 250 rpm, which is the speed that it turns at 20mph.

You must consider the mass of the rotating wheel.
More mass = more force.

[Gordon]

Some folk would argue with gravity, too, but it doesn't change anything.

[Raul CB750K1]

Interesting that a ice skating reference was used.  Certainly gyroscopic forces are in play as a skater performs a spin or a rotating jump.  And I used to know a guy that could balance a bicycle standing still, but not for more than 30 seconds or so.

Most of the people that balance a bicycle in an standstill do it with the front wheel slightly turn either to the left or right, and then they compensate by slightly applying pedaling force and the front brake. In such a position, the pedal force tend to tilt the bike in the opposite direction of the weight. Ask any of those people if they would be able to make a standstill with a bike with no chain and the front wheel locked in the straight position.

Regarding the gyroscopic effect, If you have one bicycle wheel at hand do this experiment: attach a piece of rope to only one of the sides of the axle, and tie the other end up so the wheel hangs. Leave the wheel vertical, holding by the free end of the axle while the other end hangs on the rope. Now get your hand off; the wheel will "fall" and stay in horizontal position, therefore the wheel doesn't have any balance by itself. Now, hold the wheel in the same way than before but make it spin before you get your hand off; now the wheel will stay in vertical position while it spins, and will little by little tilt as the spinning speed decreases. If the only difference in both experiments is that the wheel was spinning, it can only mean that the spinning of the wheel opposes to the force of gravity.


Anyone with a physics degree can correct me if I'm wrong (or any pilot as many of the flight instruments are based in gyroscopes), but from my memory, a gyroscope had three properties: inertia, precession and another one I cant remember. Inertia is the basic one: a spinning gyroscope tends to remain in the same plane if no external force is applied. Precession is a property by which, when you apply force to the gyroscope, this turns as is the force has been applied 90º ahead in the direction of spin. That would explain why is is necessary to countersteer to tilt the bike: if you turn the handlebar to the left, it is like if you where applying force to the back of the wheel . According to precession, the force is applied in the top of the wheel (90º ahedad), tilting the wheel (and the bike) to the right.


Raul

[merc2dogs]

it does not take 80lbs of force to change the orientation of a 27 inch bicycle wheel at 250 rpm, which is the speed that it turns at 20mph.

You must consider the mass of the rotating wheel.
More mass = more force.

  if the wheel on my bicycle is keeping it upright, then the same wheel when off the bicycle -HAS- to require the same amount of energy to change it's orientation. if two wheels are capable of of holding 160 lbs upright, then it should take 80lbs to lay on down when turning at the same speed.
 if you extend the reasoning further, it should require a lot more effort to turn the bare wheel, since the frame and forks give a very large lever effect on the wheel.

 if you have a bicycle handy, pick up the front end, or the back end get it cranking as fast as you can and SEE if it requires enough effort to hold you in position.

 in my case, if the wheels are in fact holding me up when riding, it HAS to require 80lbs effort to change the bikes position from vertical with one wheel turning, it doesn't

 I've always been the type to experiment, I do not accept something just because a hundred people say it's so, and when it is easily tested I check it out, and with the bike wheel gyroscope statement so easily put to the test I am amazed at it's continued acceptance.

 no reason to argue with gravity, it's effect is always visible.

Ken.     

   

[Gordon]

Try this test:

Take a single motorcycle wheel, or just the tire, roll it down the street and time how long it takes to fall over.
Now take the same wheel or tire, balance it standing up, let go and time how long it takes to fall over. 

[Raul CB750K1]

The gyroscope effect on a moving bicycle IS NOT ENOUGH to make the vehicle-and-driver keep the balance by itself, but provides enough inertia to let the driver compensate the center of gravity. It's like the people who walk the tightrope. Why do they hold a long rod with their hands? The rod has a lot of inertia, it takes a lot of force and torque to make it turn from its center, so it's like if the walker is indeed holding on to something that likes to stand still. Furthermore, the walker+rod center of gravity is different, and it has to move further to either side to break the balance. If you remember when you were younger and walked over a fence, by instinct you reach your arms out; the idea is the same, to make it harder to move the center of gravity out of balance.


Raul

[merc2dogs]

 

 Before anyone gets called stupid, I am NOT argueing the operation of a gyroscope, I am well aware of it's operation and it's application.

 I am argueing it's effect on the motorcycle or bicycle.

 the average wheel does NOT provide enough force to hold the bike upright.

 in the case of my bicycle, the wheel does not have the weight or the speed to hold the bike upright, and it takes far too little effort to change it's orientation, therefore it can not provide the effort required to keep the bike upright at any 'normal' speed.

ken.

[nickjtc]

I believe that this discussion is going down the wrong road. Gyroscopic precession is a fact of life with any rotating mass, in our case the wheels of the motorcycle, but is mainly a deciding factor in the ability to turn.

The larger the mass (bigger/heavier the front wheel) and the faster it is rotating = the more effort that is required to destablise it and initiate the turn....which is done by pushing on the opposite end of the handlebar to the direction the rider wants to turn. So push left, go left; push right, go right.

Gyroscopic precession of itself helps balance the motorcycle when riding in a straight line, but is not the only factor in balance, since as we all know if you goof around on the bike, or have a passenger who is not acquainted with the right way to ride back there, you can come unstuck pdq.

[Raul CB750K1]

Have you ever seen those "crashes" in races? The rear wheel skids, and as soon as it gets traction it whips the rider out of the bike, but the bike rides without rider until it crashes against the tyres or straw bales. What makes the bike keep the balance if there is no rider aboard?


Raul

[Raul CB750K1]

Why does a R/C motorcycle stay upright?


http://steliosh.net/rc/playing/cars_bike.wmv

[nickjtc]

Have you ever seen those "crashes" in races? The rear wheel skids, and as soon as it gets traction it whips the rider out of the bike, but the bike rides without rider until it crashes against the tyres or straw bales. What makes the bike keep the balance if there is no rider aboard?
Raul

Like a high-side crash. In a straight line, with no de-stabilising influence like a rider or passenger, the bike will stay upright due to the rotation of the wheels and the faster it is going the longer it will stay upright.

Likewise a r/c model.

[Gordon]

  if the wheel on my bicycle is keeping it upright, then the same wheel when off the bicycle -HAS- to require the same amount of energy to change it's orientation. if two wheels are capable of of holding 160 lbs upright, then it should take 80lbs to lay on down when turning at the same speed.
   

I think I see what you're getting at with this, but a rotating wheel does not have to hold up the entire weight of the bike and rider, it only needs to counter the slight tendency of the bike to lean to the left or right. 

Think about when you're sitting still on your bike and trying to keep it balanced.  All it takes to keep it upright is an occasional slight tap of your toe on either side to keep it from tipping over.  Now, of course, if it leans too far over you have to apply a much larger force with your leg to keep it up. 

The same applys with the gyroscopic force the wheels impart.  When they're moving slowly, the bike will fall over easier, but when they're moving fast, the bike will stay upright by itself until it either hits something, or slows down due to drag and then falls over.   

[TwoTired]

I tend to think that Gyroscopic Precession is a real phenomenon, but I was reading an article about the guy who designed the front brakes of a bike to spin backwards to offset the gyro effect of the wheels.  He said a "soundbite" that got me thinking.  He said that Gyroscopic Precession was a bunch of bunk and that a bike staying up and stable was purely a matter of balance.  He said that "Ice skates don't have wheels acting as big gyroscopes and they stay upright when moving.  It's all about balance".

Any thoughts on this?  What about his point of ice skates and gyroscopes?  Is he on to something or full of it?

He's full of it.

http://en.wikipedia.org/wiki/Gyroscope

Cheers,

[HondaMan]

Interesting that a ice skating reference was used.  Certainly gyroscopic forces are in play as a skater performs a spin or a rotating jump.  And I used to know a guy that could balance a bicycle standing still, but not for more than 30 seconds or so.

Most of the people that balance a bicycle in an standstill do it with the front wheel slightly turn either to the left or right, and then they compensate by slightly applying pedaling force and the front brake. In such a position, the pedal force tend to tilt the bike in the opposite direction of the weight. Ask any of those people if they would be able to make a standstill with a bike with no chain and the front wheel locked in the straight position.

Regarding the gyroscopic effect, If you have one bicycle wheel at hand do this experiment: attach a piece of rope to only one of the sides of the axle, and tie the other end up so the wheel hangs. Leave the wheel vertical, holding by the free end of the axle while the other end hangs on the rope. Now get your hand off; the wheel will "fall" and stay in horizontal position, therefore the wheel doesn't have any balance by itself. Now, hold the wheel in the same way than before but make it spin before you get your hand off; now the wheel will stay in vertical position while it spins, and will little by little tilt as the spinning speed decreases. If the only difference in both experiments is that the wheel was spinning, it can only mean that the spinning of the wheel opposes to the force of gravity.


Anyone with a physics degree can correct me if I'm wrong (or any pilot as many of the flight instruments are based in gyroscopes), but from my memory, a gyroscope had three properties: inertia, precession and another one I cant remember. Inertia is the basic one: a spinning gyroscope tends to remain in the same plane if no external force is applied. Precession is a property by which, when you apply force to the gyroscope, this turns as is the force has been applied 90º ahead in the direction of spin. That would explain why is is necessary to countersteer to tilt the bike: if you turn the handlebar to the left, it is like if you where applying force to the back of the wheel . According to precession, the force is applied in the top of the wheel (90º ahedad), tilting the wheel (and the bike) to the right.


Raul

Bingo!

[SD750F]

Procession is a real, and tangable effect. Take this example. The Earth has a great deal of mass rotating fairly slowly, but the gyroscopic procession is easily measurable on the 23-1/3° tilt versus the orbital plane. Now the procession of the Earth is much slower than the rotation and orbital period. This precession cycle is measured just around 23,000 years. We are about half way through one cycle right now. So in 11-12 thousand years the 23-1/3° axial tilt will be pointing the other way...

Consider this. Right now during a winter in the northern hemisphere, the axial tilt is away from the sun. And we are the closest to the sun... Yes we are! But the low angle of the sun's rays hitting the Earth's surface is spread over a larger area and in effect reduces the amount radiation and we have winter. But in 11-12 thousand years, we will be tilted away from the sun and at the greatest distance at the same time. And the opposite will be true for summer... Consider the effects that will make.

So procession exists and is demonstrable on one of the most perfect gyroscopes around, the Earth. A high mass spinning in a perfect vacuum...

Scott

[merc2dogs]

I think I see what you're getting at with this, but a rotating wheel does not have to hold up the entire weight of the bike and rider, it only needs to counter the slight tendency of the bike to lean to the left or right. 
 

  which is what I said in my first post, it contributes, but doesn't hold the entire bike/rider upright.
 at 5mph a 10 speed is perfectly rideable, at that speed a a 27 inch tire is turning  60rpm, at 60 rpm there is so little effort required to change the tires orientation that it can't contribute much at all to the overall balance of the bike.

 At higher speeds I can see a contribution, but at lower speeds there isn't enough 'resistance' to contribute.

 Got bored while waiting for a couple long slow passes to finish on the lathe so played with bike rims.

Ken.

[Bryan Boyle]

Anyone with a physics degree can correct me if I'm wrong (or any pilot as many of the flight instruments are based in gyroscopes), but from my memory, a gyroscope had three properties: inertia, precession and another one I cant remember. Inertia is the basic one: a spinning gyroscope tends to remain in the same plane if no external force is applied. Precession is a property by which, when you apply force to the gyroscope, this turns as is the force has been applied 90º ahead in the direction of spin. That would explain why is is necessary to countersteer to tilt the bike: if you turn the handlebar to the left, it is like if you where applying force to the back of the wheel . According to precession, the force is applied in the top of the wheel (90º ahedad), tilting the wheel (and the bike) to the right.


Raul

inertia, precession, and rigidity in space are the three properties.

(I'm a flight instructor as well as A&P...

[ieism]

There must be some type of gyroscopic miracle happening here, because i've never seen anyone do that on iceskates. 

http://www.youtube.com/watch?v=QrHFeO7khHI

[SD750F]

Wow! That is a fantastic example of professional riding skills!!!