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Clarification on gyroscopes

  1. Aug 7, 2015 #1
    Hi,

    I saw a video online of a self balancing 2 wheeled car. Basically a motorcycle with a body though has a steering wheel rather than handle bars. It uses two gyroscopes spinning in opposite directions to keep it's balance and was wondering if a similar thing could be adapted for regular motorcycles out of curiosity.

    I have researched on how gyroscopes work but I was wondering does the mass of the spinning disc/wheel effect how much force is being created? So assuming it is, would you need a heavy spinning mass to keep a motorcycle upright?

    Also a motorcycle or a even just a wheel can keep it's self upright if spinning fast enough same with a coin if you roll it then it remains upright. I then thought would the same effect happen if the wheel it's self was stationary but a inner cylindrical mass was spinning inside of it would it keep the wheel upright? If that's the case then would making a motorcycle wheel with a spinning inner mass in the wheel keep the bike upright?
     
    Last edited: Aug 7, 2015
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  3. Aug 7, 2015 #2

    jbriggs444

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    The video sounds like hokum. Two gyroscopes spinning in opposite directions cancel each other out. They put stress on their axle and accomplish nothing.

    Edit: That's if the gyroscope wheels are on a common axle. The mechanism in the video might not do something quite that stupid.

    The larger the mass, the more torque (or the more duration for a fixed torque) you can get out of a given amount of precession. If you are trying to keep a motorcycle upright, making the gyroscope heavy hurts as well as helps. Now you not only have to keep the motorcycle upright. You have to keep the gyroscope upright as well.

    The added value seems questionable. Motorcycles work fine without gyroscopes. And gyroscopes are not magic. Exert a constant torque on them in a fixed direction and they eventually run out of ability to resist -- they precess until their axis is lined up with the applied torque.
     
  4. Aug 8, 2015 #3

    rcgldr

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    If the coin is angled sideways enough when released it will not straighten up, but roll in a spiral like pattern as it slows down, assuming there's enough friction on the floor to keep it from sliding out.

    The steering geometry on a bike tends to keep a bike vertically oriented within a range of speeds. The common type of steering geometry is called trail, where the contact patch is behind where the steering pivot axis intercepts the pavement. If the bike is leaning, then without any rider input, the trail causes the front tire to steer inwards in reaction to the lean, enough to correct the bike back to vertical (within a range of speed). Another method used for an experiment uses a weight above and ahead of the front wheel, which doesn't have any caster or trail, and when this bike leans, a yaw torque due to the weight causes the front tire to steer inwards.

    Gyroscopic reaction causes the front wheel to steer in the direction of roll torque, but once the turn is coordinated, the roll torque goes to zero, so the gyroscopic effect tends to hold a coordinated turn instead of correcting the bike back a vertical orientation. At most speeds, the rate of precession while a bike leans over is slow enough that the net effect is that it slows down the geometry related steering reaction. When the geometry related steering is inwards enough to produce an outwards roll torque needed to correct the lean back to vertical, the geometry related steering reaction is trying to steer outwards of the current steering angle. The net effect is that gyroscopic reaction opposes the geometry based reaction, but within a speed range, the geometry based reaction dominates and the gryoscopic reaction acts as a damper, just slowing down the correction as opposed to preventing it.

    At high speeds, gyroscopic reaction dominates, and self stability is lost (called capsize mode). The bike falls inwards at a very slow rate, and the rate may be so slow that's it's imperceptible to the rider, and the bike appears to hold the current lean angle until the rider uses counter steering to return to vertical orientation. Body leaning which indirectly countersteers a bike, ceases to work at high speeds, and only direct counter steering by the rider works.
     
    Last edited: Aug 8, 2015
  5. Aug 8, 2015 #4

    A.T.

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  6. Aug 8, 2015 #5

    A.T.

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    Or a smaller mass spinning faster.
     
  7. Aug 8, 2015 #6

    Nidum

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  8. Aug 8, 2015 #7

    rcgldr

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    The gyroscopes are not self-stable devices. Instead they are mounted in powered gimbal assemblies (and a motor within the gimbal assemblies to keep the gryo's spinning). Looking at the image, the gyro's have a near vertical (yaw) axis. The gimbal assembly motors exert a torque (as needed) about a left right (pitch) axis, resulting in a reaction torque (as needed) about the roll axis, which is used to stabilize the bike.
     
    Last edited: Aug 8, 2015
  9. Aug 8, 2015 #8

    sophiecentaur

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    The title of this thread strikes me as a real oxymoron.
    "Clarification"? That's something I would love to see.:wink::wink:
     
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