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Thread: Gyroscope question

  1. #1 Gyroscope question 
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    I've always thought of bicycling as riding two gyroscopes. Here's my question: Can there be a speed difference by moving weights from hub to rim? And back again? I pictured weights on each spoke, and by some means, as the wheels stablize, they move up to the hub. Any ideas? Thanks.


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  3. #2  
    exchemist
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    Quote Originally Posted by william craig View Post
    I've always thought of bicycling as riding two gyroscopes. Here's my question: Can there be a speed difference by moving weights from hub to rim? And back again? I pictured weights on each spoke, and by some means, as the wheels stablize, they move up to the hub. Any ideas? Thanks.
    Balancing a bicycle has nothing to do with gyroscopes. What you do is to steer the bike back underneath you, as soon as it starts to tip. That is why you need to be moving, and why you cannot ride a bicycle if the steering is locked in position. In fact if you watch somebody balancing a bike at very low speed, you will notice they have to make quite vigorous steering motions to keep the bike vertically underneath them all the time. It is the same process as balancing a pencil on your finger.

    I am not sure exactly what you mean by a "speed difference" if you move weights from hub to rim and back. If you move weights from hub to rim you will increase the moment of inertia of the wheel, which means it will rotate more slowly for a given amount of angular momentum, in other words it will require an input of rotational kinetic energy to maintain its speed. This will therefore tend to slow the bike down. Conversely moving the weights from rim to hub will reduce the moment of inertia which will tend to speed it up.

    P.S. If gyroscopic effects were important then every time you tried to turn left the wheel would tip to the right and you would fall off.


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  4. #3  
    Forum Cosmic Wizard
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    Quote Originally Posted by william craig View Post
    I've always thought of bicycling as riding two gyroscopes.
    The gyroscopic effect has very little to do with bicycle stability, especially at low speed. It's mostly gravity and human input.

    Many bikes are inherently stable; that's why you can ride them "hands-off." This has a lot to do with a design parameter known as "trail." As the bike starts to tip to one side, the force on the front wheel becomes a little off-center and tends to turn the wheel towards the "low" side. This rebalances the bike.

    Here's a bizarre little factoid: On a bike you can steer by weight shift. But if you don't use weight shift at all, to turn left, you first have to turn the handlebars to the right.
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  5. #4  
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    Quote Originally Posted by william craig View Post
    I've always thought of bicycling as riding two gyroscopes. Here's my question: Can there be a speed difference by moving weights from hub to rim? And back again? I pictured weights on each spoke, and by some means, as the wheels stablize, they move up to the hub. Any ideas? Thanks.
    moving weights away from hub would absorb energy from the system, the bike would slow down and vice versa
    gyroscopic effect remains constant, because of constant amount of energy supplied (assumed)
    stability is not from gyroscopic effect
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