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Extracting energy from gyroscope precession

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Precision99

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I chanced upon an earlier thread entitled Gyroscopic Precession. In the discussion, someone proposed attaching a generator to the axis of precession rotation. If a load is connected to the generator, then it will create an opposing torque drag on the precession rotation. Work has thus been done by the generator, and energy has moved from the gyroscope, to the generator. One poster, think it was c_mitra, stated that this energy must come from the rotation of the spinning gyrospcope wheel, which as a consequence would slow down.

I disagree. The gyroscope rotor is supported by bearings. For the purpose of this discussion these bearings are assumed frictionless. By definition of what a bearing is and what a bearing does, there can be no torque transmitted from the shaft to the rotor, and as nothing else is in physical contact with the rotor, there can be no torque imparted to the rotor, period, and thus the proposition that braking the precession rotation will cause the gyro rotor to slow down (angular deceleration) must also be wrong.

Anyone care to comment on this? What exactly will happen if you oppose the precession rotation, and where will any energy thus extracted come from?
 
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Kajunbee

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I chanced upon an earlier thread entitled Gyroscopic Precession. In the discussion, someone proposed attaching a generator to the axis of precession rotation. If a load is connected to the generator, then it will create an opposing torque drag on the precession rotation. Work has thus been done by the generator, and energy has moved from the gyroscope, to the generator. One poster, think it was c_mitra, stated that this energy must come from the rotation of the spinning gyrospcope wheel, which as a consequence would slow down.

I disagree. The gyroscope rotor is supported by bearings. For the purpose of this discussion these bearings are assumed frictionless. By definition of what a bearing is and what a bearing does, there can be no torque transmitted from the shaft to the rotor, and as nothing else is in physical contact with the rotor, there can be no torque imparted to the rotor, period, and thus the proposition that braking the precession rotation will cause the gyro rotor to slow down (angular deceleration) must also be wrong.

Anyone care to comment on this? What exactly will happen if you oppose the precession rotation, and where will any energy thus extracted come from?

Are you speaking of @cmitra reply of post #6. If so I don't think he realized there would be a motor maintaining rpm of wheel when he replied. I made a device like the one in YouTube video, but attached to a permanent magnet generator. I was not able to achieve constant precession with generator loaded or unloaded. Something I did notice was that wheel seemed to slow down when I forced the precession rate with my hand. As I forced the precession the device would move in and upwards arc. At one point I forced the precession rate to such a degree that the gyro motor almost came to a complete stop. I didn't think much of it at the time. Thought maybe it was because of my flimsy construction. But your post has me wondering if the forced precession was causing a force that opposed the rotation. I wouldn't think this was possible but gyros are strange beast.
 

Easy peasy

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any precession will necessarily be slow ... (?) thus the ability to get energy from it is limited. One assumes you are not talking about the normal rotation ....
 

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thus the ability to get energy from it is limited
Sure, but the problem is at least of theoretical interest. Kajunbee's empirical observation that braking the precession slows down the gyro rotation can be substantiated by the theory of gyroscopic motion. The classical treatments are already mentioned in the previous thread, there are particularly Klein/Sommerfeld, Theorie des Kreisels (1897) and Crabtree, Spinning Tops and Gyroscopic Motion (1909), both available at archive.org.

For an engineer or natural scientist, conservation of energy law is usually a sufficient explanation. Phenomena like gyroscopic motion which involve non-trivial physical analysis are continuously attracting "free energy" and over-unity fans who are deaf to general conservation of energy considerations. Thus it's interesting to show the energy transfer also in terms of motion equations.
 

c_mitra

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Are you speaking of @cmitra reply of post #6. If so I don't think he realized there would be a motor maintaining rpm of wheel when he replied.

I am sorry that I am not understood.

Motor is a source of energy. A gyroscope must be free (from external forces)- I am talking about mechanical gyroscopes here.

A spinning object mounted in vacuum (no friction) will maintain its direction.

The angular momentum vector is along the axis of rotation.

Precession of a top is due to gravity; if the angular momentum vector is at an angle with the direction of the gravitational force, precession takes place. If the top is rotating exactly vertical, there will be no precession.

If you average over one precession period, you will see that the original angular momentum vector is still vertical.

What causes the top to tilt in the first place? The top is in an unstable orientation and any small perturbation will cause it to move away from the rotation axis.

If you couple a motor to the rotating wheel, it is no more free and you can supply or remove energy from the gyroscope and change its orientation. But then it will no more be a gyroscope.

The small errors are cumulative.

It is interesting to study laser gyroscopes and how do they determine the rotation axis of the earth.
 

dick_freebird

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There are certainly gyroscopes which are motorized to keep
them spinning (look in any inertial measurement unit prior to
2000-ish fielding; optical and MEMs "gyros" are late to the
party).
 

Easy peasy

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Gyro scopes can be magnetically coupled to coils that can speed up or receive energy from the gyroscope - this approach is now widely used in industry - up to 100kW - a lot of effort is used to ensure any precession that occurs is very small - indeed even a child's top will settle to vertical motion if there is enough energy in the system - the idea of extracting energy from the precession alone is not a good one.
 

Kajunbee

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Gyro scopes can be magnetically coupled to coils that can speed up or receive energy from the gyroscope - this approach is now widely used in industry - up to 100kW - a lot of effort is used to ensure any precession that occurs is very small - indeed even a child's top will settle to vertical motion if there is enough energy in the system - the idea of extracting energy from the precession alone is not a good one.

Can you provide a link or more exact search description.
 

std_match

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The force that drives the precession rotation comes from the downward movement of the "free" end of the gyro.
This means that any energy that is extracted comes from the loss of potential energy for the mass of the gyro.
The rotational energy of the gyro is not involved, and it will not slow down due to stopping the precession rotation or not.
Any forces applied will affect the bearings, so the friction in normal bearings will make the gyro slow down faster when forces are applied.

If you have an extremely large gyro supported at both ends, it should be possible to extract some energy from the earth rotation, but that isn't precession.
 

Precision99

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The force that drives the precession rotation comes from the downward movement of the "free" end of the gyro.
This means that any energy that is extracted (from the precession rotation) comes from the loss of potential energy for the mass of the gyro.
The rotational energy of the gyro is not involved, and it will not slow down due to stopping the precession rotation or not.
Any forces applied will affect the bearings, so the friction in normal bearings will make the gyro slow down faster when forces are applied.

If you have an extremely large gyro supported at both ends, it should be possible to extract some energy from the earth rotation, but that isn't precession.

I agree with all you say. Assuming frictionless bearings, you cannot speed up or slow down the gyro rotor by way of ANY motion that you force upon the axle, including slowing down or speeding up the precession speed.

And I also agree that the precession rotation is driven by gravity, by the fall in the centre of gravity of the gyro, a nice example of mgh. With frictionless bearings, no energy is ever transferred from the rotational speed of the rotor to or from the precession motion.

Note that the total kinetic energy of the gyro is the sum of the rotational energy of the rotor (0.5Iw^2) AND the rotational energy of the precession rotation. So if you forcibly slow down the precession speed, then you can and will extract energy from the kinetic energy stored in the precession rotation, as well as mgh energy from the drop in height of the free end of the axle, if it is permitted to drop.

So then we need to ask, where did the kinetic energy stored in the precession rotation come from in the first place? For example, hold a spinning bicycle wheel with a hand supporting and holding both ends of the axle - precession speed equals zero. Then, release one hand so that the axle is now supported at one end only. The wheel will now start to precess, so the total kinetic energy has increased. And that increase in total kinetic energy will and must be accompanied by a drop in the level of the unsupported end of the axle. So the increase in total kinetic energy has come from a decrease in gravitation potential energy, NOT from a slowing down of the rotor speed.

My original point appears sound. With frictionless bearings, there is never any transfer of energy from the spinning gyro rotor (or bicycle wheel) to anything at all, including precession rotation. You don't need to know any physics at all to confidently make that statement. All that is required is an understanding of what a bearing does, which is to ensure that no torque can ever be transmitted from axle to rotor. And with no torque transmittted to rotor, the rotor cannot be made to speed up or slow down.

Or can it? Not with a conventional gyroscope, but I believe that a machine CAN be made, with frictionless bearing, where a torque CAN be transmitted to a rotor, and the rotor be thus made to rotationally speed up. And without cheating like using magnetic forces (electric motor) or wind forces (turbine wheel) or any other cheating nonsense where something mechanically touches the rotor, or where a magnetic or electric or any other sort of field produces a force on the rotor. And no use of gravity, either. Just by appropriate machine design, and appropriate forced motion of the axle. Anyone care to comment on that?
 

Kajunbee

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The force that drives the precession rotation comes from the downward movement of the "free" end of the gyro.
This means that any energy that is extracted comes from the loss of potential energy for the mass of the gyro.
The rotational energy of the gyro is not involved, and it will not slow down due to stopping the precession rotation or not.
Any forces applied will affect the bearings, so the friction in normal bearings will make the gyro slow down faster when forces are applied.

If you have an extremely large gyro supported at both ends, it should be possible to extract some energy from the earth rotation, but that isn't precession.

That is what I thought may have caused motor to slow. The wheel was only supported on one side by motor shaft. Forcing the precession must have put a great deal of stress on bushings/bearings and shaft of motor. Possibly even to the point where rotor started to drag. The motor shaft was 3 mm mounted to a 6" bench grinding stone.
 
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Precision99

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If you have an extremely large gyro supported at both ends, it should be possible to extract some energy from the earth rotation, but that isn't precession.

Can you eleborate? Just say I am standing at one pole, and holding a fast spinning bicycle wheel, by holding both ends of the axle. And the axle is horizontal, that is, at right angles to the axis of the earth's rotation. Is this the arrangement you had in mind?


So far so good, but now you need to explain how you intend to extract energy from the earth's rotation.

Presumably you would argue that the spinning wheel resists the rotation of the earth, and that therefore energy can be extracted. But provided the axle stays horizontal (ie at right angles to the earth's axis) the spinning wheel does NOT resist the rotation of the earth at all. The axis of the torque reaction on the axle is at RIGHT ANGLES to the rotational axis of the earth, and therefore does not resist rotation about the earth's axis, and therefore no energy can be extracted.

But I am only guessing as to how you believe energy can be extracted from the earth's rotation using a gyro, which I take to effectively be a spinning bicycle wheel. It is up to you to elaborate on how you think it can be done, and then we can comment on your proposal.
 

BradtheRad

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For example, hold a spinning bicycle wheel with a hand supporting and holding both ends of the axle

This jogs my memory about a mystifying physics demonstration. Sit on a free-turning chair, feet off the floor. Start a bicycle wheel spinning with your hand. It becomes a gyroscope. By orienting it in various directions, your chair turns as if by magic.

Hold the wheel one way and you go clockwise.
Hold it another way and you go counter-clockwise.


Regardless of what the law of conservation of energy says, we can't help thinking some secret source of power is at work.
 

std_match

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Presumably you would argue that the spinning wheel resists the rotation of the earth, and that therefore energy can be extracted. But provided the axle stays horizontal (ie at right angles to the earth's axis) the spinning wheel does NOT resist the rotation of the earth at all. The axis of the torque reaction on the axle is at RIGHT ANGLES to the rotational axis of the earth, and therefore does not resist rotation about the earth's axis, and therefore no energy can be extracted.

A force is always needed to change the spinning plane of a gyro. During that change a perpendicular force is created (the one that tries to tilt the axis from the horisontal position). If you allow the tilting of the spinning axis or not doesn't affect the fact that a force is needed to change the spinning plane of the gyro.
 

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as you try to turn the axis of the bike wheel you encounter an opposing force against which you push - this is transferred through your body to the chair - allowing the rotation of the chair to be slowed or reversed - when the wheel axis is held vertically the two angular momentums combine to either help the chair around in the direction it was going or (opposing ) to slow and reverse the chair - limited by friction ....
 

Kajunbee

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Or can it? Not with a conventional gyroscope, but I believe that a machine CAN be made, with frictionless bearing, where a torque CAN be transmitted to a rotor, and the rotor be thus made to rotationally speed up. And without cheating like using magnetic forces (electric motor) or wind forces (turbine wheel) or any other cheating nonsense where something mechanically touches the rotor, or where a magnetic or electric or any other sort of field produces a force on the rotor. And no use of gravity, either. Just by appropriate machine design, and appropriate forced motion of the axle. Anyone care to comment on that?

I'm listening.
 

asdf44

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Seems like this poster isn't interested in the law of conservation of energy.


Intuitively I think of examples like a hula-hoop where you can accelerate or decelerate its rotational speed without exerting any direct rotational torque. I have a feeling this example is masking a similar concept.
 

Easy peasy

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Or can it? Not with a conventional gyroscope, but I believe that a machine CAN be made, with frictionless bearing, where a torque CAN be transmitted to a rotor, and the rotor be thus made to rotationally speed up. And without cheating like using magnetic forces (electric motor) or wind forces (turbine wheel) or any other cheating nonsense where something mechanically touches the rotor, or where a magnetic or electric or any other sort of field produces a force on the rotor. And no use of gravity, either. Just by appropriate machine design, and appropriate forced motion of the axle. Anyone care to comment on that?

please point me to the frictionless bearings and the part where anything spinning in air has no frictional losses .... my credit card is ready ...
 

Precision99

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A force is always needed to change the spinning plane of a gyro. During that change a perpendicular force is created (the one that tries to tilt the axis from the horisontal position). If you allow the tilting of the spinning axis or not doesn't affect the fact that a force is needed to change the spinning plane of the gyro.

Quite so. We are completely in agreement, but noting that the "opposing force" is at right angles to your movement of the axle, so no work is done. Indeed, strictly speaking, the gyroscopic effect does not "oppose" your motion of the axle at all, because there is no component of opposing torque in the direction of your angular movement of the axle.

OK. So getting back to your suggestion that a sufficiently large gyro (a spinning bicycle wheel) could be used to harness energy from the earth's rotation. Can you elaborate on how you intend to do that?
 

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