Bicycle Wheel; Gyroscopic Action

[LareeRudi]

Homework Statement

Bicycle traveling 20 ft/sec. Moment of Inertia of the front wheel is 0.25 slug*ft^2. Wheel radius is 15 inches. With what angular velocity must the front wheel be turned about a vertical axis to counteract the capsizing torque due to a 120 pound person being 1 inch horizontally off center [to left or right] of the line of contact of wheels and ground?

Bike riders; does it make sense? [asked in the problem, not by ME].

Homework Equations

I'm not really sure, but...

L=I*omega
for the person, Torque = Weight x distance
T=120*(1/12) = 10 ft*lbs This is what the gyro action needs to overcome
I can't "see" beyond this.

The Attempt at a Solution

I'm trying to use gyroscopic equations, rotational momentum, but I admit (college in 1955) that I never learned about these gyroscopes and the required vectors; you can see I'm not cheating on any homework; me, 72 plus years old, just don't know how to get started.

What blows MY mind, is why do they state the forward velocity, and then ask [indirectly] what the velocity needs to be to offset the person being off center by one inch. It'll be DIFFERENT than the forward velocity they give. Is it extraneous info? by accident? to trip you up? or is it essential?

Am I in the right place? They say to use "Homework" section even if it's only "Homework" style? A lot of the stated questions in this forum seem to be pretty far above what I'm asking.

[edit for spellig]

thx,

LarryR : )

 

[LareeRudi]

OK, no takers; so then perhaps you can help me get STARTED; how about this question. On a gyroscope, we have the weight of the spinning wheel aiming downwards, P force UPWARDS happening by the bicycle fork? then you have L which I believe is Angular Momentum, but it appears to be a vector aiming OUT of the axle.

So WHAT or WHERE is the force from the gyroscope that is conteracting the person that is leaning over [that 1 inch beyond the centerline of the bicycle]?

I'm COMPLETELY LOST.

thx,

LarryR : )

 

[Quinzio]

Hello Larry,
this place is quite crowded as you can see, so you don't have to worry if your questions don't receive any answer.
Well let's talk about bicycles.
A gyroscope is a quite interesting object which is not so easy to understand, but as long as you become acquainted with it, it is less mysterious but as well fascinating.
As a bicycle wheel is spinning it experiences the so called gyroscopic effect.
Before continuing you have to notice that this is just a "theoretical" experiment. A bicycle wheel is spinning slowly and the gyroscopic effect is little. No one riding a bicycle ever notice it.

Imagine you are on a bicycle. The front wheel is spinning. Using the handle bar, if you steer the front wheel let's say toward left, the wheel as a gyroscope reacts with a force (a torque) which is trying to make you fall on the right side.
This torque is originated in the wheel itself. Through the fork, this fork affects all the bicycle which is push to the right.
Notice the axis of the various forces: the wheel spinning axis is horizontal (left-right), you are moving the handle bar vertically (up-down), the reaction torque is horizontal (front-back). This is basically the gyroscope. If you apply a movement (a precession) which is right angled to the spinning axis, you get back a force which is perpendicular to both (the spin axis and your torque).

Now you can check the youtube videos about "gyroscope" and "bicycle stability" which are quite interesting.
Such as this one:
Why the bicycle doesn't fall ?

 

[LareeRudi]

Hello Larry,
this place is quite crowded as you can see, so you don't have to worry if your questions don't receive any answer.
Well let's talk about bicycles.
A gyroscope is a quite interesting object which is not so easy to understand, but as long as you become acquainted with it, it is less mysterious but as well fascinating.
As a bicycle wheel is spinning it experiences the so called gyroscopic effect.
Before continuing you have to notice that this is just a "theoretical" experiment. A bicycle wheel is spinning slowly and the gyroscopic effect is little. No one riding a bicycle ever notice it.

Imagine you are on a bicycle. The front wheel is spinning. Using the handle bar, if you steer the front wheel let's say toward left, the wheel as a gyroscope reacts with a force (a torque) which is trying to make you fall on the right side.
This torque is originated in the wheel itself. Through the fork, this fork affects all the bicycle which is push to the right.
Notice the axis of the various forces: the wheel spinning axis is horizontal (left-right), you are moving the handle bar vertically (up-down), the reaction torque is horizontal (front-back). This is basically the gyroscope. If you apply a movement (a precession) which is right angled to the spinning axis, you get back a force which is perpendicular to both (the spin axis and your torque).

Now you can check the youtube videos about "gyroscope" and "bicycle stability" which are quite interesting.
Such as this one:
Why the bicycle doesn't fall ?

Please realize, everybody, that I have not reached "amateur" status, I'm probably less than a "beginner", but I'm not CONVINCED [who am I, LOTS of people are far more intelligent than me, but...] that it IS gyroscopic effect that keeps the bicycle upright, I think that because of the "rake" and "trail" of the Head and Fork design, the handlebars are "self correcting" for any moment that the bike want's to go "off course".

What would happen if the handlebars were rigidly attached [glued, welded, clamped] so that they could not rotate at all? I'm THINKING that the bike will fall [but I don't KNOW that]. So then I would ask, what happened to the gyroscopic effect of the wheels in THAT scenario?

I value your opinion, or your stated belief/knowledge.

I MUST SAY, that video was VERY interesting; I've never seen anything like that in my past 72 plus years. Thanks for showing me.

Just trying to learn.

[edit; spellig]

thx

LarryR : )

 

[Cleonis]

[...]I think that because of the "rake" and "trail" of the Head and Fork design, the handlebars are "self correcting" for any moment that the bike want's to go "off course".

To my knowledge that is what the experts indeed say: the front wheel is a trailing wheel.

Also, when the geometry is well designed the bike has the following property: the sheer weight of the bike keeps the front wheel aligned.
That is: if you keep the bike as a whole upright, and you turn the front wheel, the center of gravity rises slightly. Because of that a bike's front wheel has no tendency to flop left or right, as long as it's carrying weight.
However, when you lean the bike the balence comes out in such a way that the center of gravity is lowest when the front wheel is slightly turned in.

It's those properties that give a rolling bicycle its tendency to stay upright automatically.

What would happen if the handlebars were rigidly attached [glued, welded, clamped] so that they could not rotate at all? I'm THINKING that the bike will fall [but I don't KNOW that]. So then I would ask, what happened to the gyroscopic effect of the wheels in THAT scenario?

Yeah, with the front wheel prevented from turning sideways the bicycle will keel over right away.As I understand it for bicycles gyroscopic effect is pretty much irrelevant. One early researcher tried that out as follows. He constructed a bicycle with a counterrotating secondary front wheel. The "secondary front wheel" didn't touch the ground, it was just there to cancel the angular momentum of the actual front wheel. With some gearing the secondary front wheel was rotating with the same velocity as the actual front wheel, but in the opposite direction.
That researcher wrote that the bicycle handled like a normal bicycle. He could feel the extra weight, but other than that the steering felt the same.Now, when a fixed-handlebars-bicycle keels over there is a gyroscopic effect, but that doesn't affect the keeling over.
When the rolling bicycle is keeling over there are two motions: the rolling of the bicycle and the keeling over. Those two motions combined give rise to a torque that tends to turn the wheel, but since the wheel is prevented from turning the wheel doesn't turn. So there is no opportunity for the gyroscopic effect to have any effect.