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> Bicycle Balancing, gyroscope explanation
boit
Posted: Jan 31 2010, 07:16 AM


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QUOTE (Enthalpy @ Jan 30 2010, 11:32 PM)
One easy experiment is to turn the front wheel when holding the bicycle at its frame, and incline the frame: observe the wheel's reaction.

I just did that and observed that if I lean the frame towards me the front part of the wheel turns towards me. It turn to the opposite direction when I leaned the bike to the opposite direction (away from my body).

Then I repeated the experiment without the wheel turning and guess what? The same thing happened albeit rapidly. To convince the skeptic who may think the curve of the folk forward (made that way to reduce trail) is the explanation to both experiment, I rotated the wheel in the reverse direction. The result was impressive Leaning the bike towards me made the front of the wheel turn away from me (that is the handle bars turned clockwise).

Now what will happen if an acrobats tries to coast downhill in reverse and wants to turn say to his left. Which direction will he lean the bike?


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Boit was last taught physics in class way back in 1994. Whatever he's learnt thereafter is purely by personal effort through this forum and searching the net. He is not an authority in any matter science. Unless with clear referrence, what he puts forward is his own understanding of what he has read and may not always be correct. Peace.
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iseason
Posted: Jan 31 2010, 08:30 AM


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QUOTE (flyingbuttressman @ Dec 17 2009, 07:52 AM)
One thing you could do is add "spinners" to the tires. These would be equal to or greater than the mass of the tires, and would look like disks with almost the same radius as the tire. They would have a ratchet mechanism that would let them spin independently of the tires, but would allow them to gain angular momentum when the bicycle is in motion. With 4 of such devices (1 on each side of each tire), you might be able to stay upright when stopped until the spinners slow down.

Edit:
http://www.engadget.com/2006/04/28/gyrobik...es-self-steady/

hi all



This question and answers ignores other examples where motion equals being upright or an easier sense of balance...Namely , skating ,snow boarding. water sports. All of these have no action , such as the wheels to keep the person upright,yet in each example,you will fall over or sink without motion.

A bike will not stay upright without CONSTANT adjustment by the rider as to it's orientation.So too for the other examples. Try riding a bike with stiff steering.Motion gives you a longer responses window to make the adjustments. It also increases the traction of the wheels when the angles are increased, such as taking a sharp corner.

Since change in angular motion leaves residual energy in the direction of original travel,it transfers to the portion of the wheel which is still in contact with the ground.However,There is no reason to assume that the contact with the ground negates the momentum in the rest of the mass of the bicycle and rider.(try hitting the brakes).
The greater the speed,The stronger the angle required to remain upright in a bend...

All of this is controlled by the rider.....Nothing in any of this allows that the turning wheels "gyroscope or not' will hold a bike on it's own without a constant impute from an outside source which checks and rechecks orientation.

One thing that will is Newton's law of equal and opposite forces.A deviation from upright needs an equal correction opposite the deviation. For a bike to stay upright, the rider "over corrects",and then "over corrects" again and again. If this were not so ,then we could find the exact center and leave our bikes upright all the time.

A sideways metronome would work.

What you need to do is be able to change the effect to mimic the 'over correcting' that we do as we ride. The lenght of the rod would bias towards the top or bottom , depending where the over correction were needed.Thinking as I type, A vertical or horizontal metronome would act similarly.either one would "kick" the bike sideways in small increments.. The speed of the adjustments must be geared to the speed of the bike ,requiring a much faster cycle when going slow than when moving rapidly.

In fact , any speed within reason will do the same thing , but will be much more noticeable if slow adjustments are used and would create a smooth ride if the adjustments are equal to the speed of the wheels.Such adjustments could be handles by the spinners suggested in the post I am answering.(however the spinners are used to create sideways/up and down motion as a result of their momentum

Cheers
Iseason

This post has been edited by iseason on Jan 31 2010, 08:37 AM
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MikeO
Posted: Feb 3 2010, 06:40 PM


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Over 20 years ago I saw a thumbnail article in Scientific American on this issue. The author made a special bicycle that had parallel wheels mounted in front and back next to the normal wheels, but they were slightly smaller and didnít reach the ground.

These auxiliary wheels were geared to turn at the same velocity as the regular wheels, BUT IN THE OPPOSITE DIRECTION. They were weighted to compensate for their smaller size, and thus achieved the exact same angular momentum as their partner wheels.

So these auxiliary wheels exactly cancelled out all the angular momentum the regular wheels generated. The results were profoundly unexpected. There was NO DIFFICULTY in riding and balancing on this zero angular momentum bike, a quadricycle.


***


Next, the author started experimenting with the caster or camber (I forget which) of a normal bicycle. He discovered that when the turning fork of the front wheel was pointed straight down he couldnít balance the bike one bit at all.

The balance of a bicycle is due NOT TO ANGULAR MOMENTUM, but to the slight angle the fork is pitched at. When a rider leans too far to one side, the fork pitch self-corrects it.

I saved the article somewhere, but canít find it. If I do Iíll return with it.
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flyingbuttressman
Posted: Feb 3 2010, 07:16 PM


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QUOTE (MikeO @ Feb 3 2010, 01:40 PM)
These auxiliary wheels were geared to turn at the same velocity as the regular wheels, BUT IN THE OPPOSITE DIRECTION. They were weighted to compensate for their smaller size, and thus achieved the exact same angular momentum as their partner wheels.

So these auxiliary wheels exactly cancelled out all the angular momentum the regular wheels generated. The results were profoundly unexpected. There was NO DIFFICULTY in riding and balancing on this zero angular momentum bike, a quadricycle.

Umm, no. Rotating the auxiliary wheels will actually add to the gyroscope effect. If you want to cancel out the effect, try to balance on the bike when it's not moving.


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MikeO
Posted: Feb 3 2010, 07:19 PM


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The auxillary wheels spin in the direction opposite to the normal wheels.

The angular momentum vectors are pointed in opposite directions and cancel.

The guy designed a zero angular momentum bike.

This post has been edited by MikeO on Feb 3 2010, 07:22 PM
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flyingbuttressman
Posted: Feb 3 2010, 07:51 PM


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QUOTE (MikeO @ Feb 3 2010, 02:19 PM)
The auxillary wheels spin in the direction opposite to the normal wheels.

The angular momentum vectors are pointed in opposite directions and cancel.

The guy designed a zero angular momentum bike.

That's not how a bike works. Bicycles rely on the gyroscopic effect to remain upright. Running wheels in opposite directions does not cancel it out.


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MikeO
Posted: Feb 3 2010, 08:11 PM


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The author of the Scientific American article I cited was challanging the common belief that bicycle balance relies on the gyrosacopic effect, as you posted. Nearly every textbook says this as well. He proved that this belief is wrong.

He proved that when angular momemtum is removed with a 4 wheel bike, it still balances due to the angle of the turning fork.

He proved that there's not enough angular momentum in the wheels of a regular bicycle to balance a rider with his vertically mounted turning fork.

Do you know about angular momentum being a vector, a directed quantity? Two oppositely spinning gyroscopes can cancel each other's angular momentum out if they are mounted pointing in the same direction.

I'll have to search for that article. If there are any machinsts out there who can duplicate his experiment that would also help.
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flyingbuttressman
Posted: Feb 3 2010, 08:30 PM


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QUOTE (MikeO @ Feb 3 2010, 03:11 PM)
The author of the Scientific American article I cited was challanging the common belief that bicycle balance relies on the gyrosacopic effect, as you posted. Nearly every textbook says this as well. He proved that this belief is wrong.

You didn't cite any article.
QUOTE
He proved that when angular momemtum is removed with a 4 wheel bike, it still balances due to the angle of the turning fork.

Then why can't you balance on a stationary bike?
QUOTE
Do you know about angular momentum being a vector, a directed quantity? Two oppositely spinning gyroscopes can cancel each other's angular momentum out if they are mounted pointing in the same direction.

On second thought, there may be some truth to this, but I still haven't seen any evidence.


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MikeO
Posted: Feb 3 2010, 08:42 PM


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I admit my citation was poor. I do know it was in Scientific American, it was a long time ago, and it was not a regular size article. It was a small news item type article.

If anyone here can search through old SciAm issues, it may have even been 40 years ago.

The reason you can't balance on motionless bike is because the self correcting action of the turning fork pitch is out of commission. It works by auto steering into a fall.
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rpenner
Posted: Feb 3 2010, 09:16 PM


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David E. H. Jones "The Stability of the Bicycle" Physics Today 23 (April,1970) p34-40.
Or fancy reprint:
http://www.phys.lsu.edu/faculty/gonzalez/T...59no9p51_56.pdf

Also:
http://www2.eng.cam.ac.uk/~hemh/gyrobike.htm


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flyingbuttressman
Posted: Feb 3 2010, 09:20 PM


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QUOTE (rpenner @ Feb 3 2010, 04:16 PM)
David E. H. Jones "The Stability of the Bicycle" Physics Today 23 (April,1970) p34-40.
Or fancy reprint:
http://www.phys.lsu.edu/faculty/gonzalez/T...59no9p51_56.pdf

Also:
http://www2.eng.cam.ac.uk/~hemh/gyrobike.htm

I stand corrected.

Thanks!


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MikeO
Posted: Feb 3 2010, 10:05 PM


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Thanks rpenner!

I wonder if that's the same guy I saw in SciAm.

I'm going to still search for my article.
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iseason
Posted: Feb 4 2010, 04:30 AM


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QUOTE (MikeO @ Feb 4 2010, 11:05 AM)
Thanks rpenner!

I wonder if that's the same guy I saw in SciAm.

I'm going to still search for my article.

Hi all

something neglected in most arguments is variation. There are three distinctly different variations (not counting outside conditions). Speeding up,Slowing down and Cruising.
Speeding up (peddling) requires much more correction than the other two because the forces are non directional except along the rigid frame. They act upon the front wheel to cause friction ,which will turn it towards whichever side has the least.

The frame will still continue to move in a straight line regardless of the front wheels turn. The art of riding a bike is keeping "the front wheel" traveling in the same direction as the back ".....Although this seems strange, the bike always has you the rider, and the frame , in total harmony..all you ever do is prevent friction from turning the front of the bike away from the direction you want to travel. This is why you can ride without your hands on the steering.

think about this. You change the bikes direction With pressure via your knees.The trick has more to do with getting the front to follow the new direction that you choose for the frame of the bike.

As well as that slowing down (not peddling) means that the bike is more. The rear of the bike is pulling back on the front wheel (in conventional design)...Which will hold it straighter.....The more rear pressure (braking) the straighter the line of the front wheels orientation....Of course the reverse is also true..The more forwards the friction(braking) , the less the control.

Cheers
Iseason
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Makings
Posted: Feb 4 2010, 05:46 AM


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Has anyone ever seen a unicycler balance? If your skilled enough im sure you could keep a bike balanced when its stoped moving but it would probably take so much effort it wouldnt be worth doing.
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light in the tunnel
Posted: Feb 4 2010, 03:47 PM


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QUOTE (Makings @ Feb 4 2010, 05:46 AM)
Has anyone ever seen a unicycler balance? If your skilled enough im sure you could keep a bike balanced when its stoped moving but it would probably take so much effort it wouldnt be worth doing.

This is just a guess but I have the idea that balancing on a unicycle is facilitated by being able to pedal in both directions to "catch" falls in any direction. Since a bicycle usually only pedals in one direction, I believe some amount of forward motion would be needed to catch such falls.
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