Timeline for Dynamics of counter-rotating flywheels
Current License: CC BY-SA 3.0
9 events
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| Oct 8, 2013 at 7:08 | comment | added | gregsan | that's why you use a second, counter rotating flywheel so the both precession forces cancel each other on the system level. this precession force doesnt oppose your applied torque (because it is orthogonal). it changes its direction--that gives it the illusion that it is harder to torque, a phenomenon that disappears when there are two flywheels. any perceived increased difficulty to torque the system would simply be due to there being twice as much mass and therefore moment of inertia. | |
| Oct 7, 2013 at 20:59 | comment | added | user1055643 | If you constrain a (single wheel) gyroscope to resist the precessional force, you still need to apply many times more torque to rotate it (orthogonally to its primary axis) than you would do if it were at rest. I don't see how adding a second flywheel rotating in the opposite direction would reduce that required torque -- I think it would double it. | |
| Oct 7, 2013 at 9:06 | comment | added | gregsan | you are mistaken...the force that makes it feel "much more massive" is precisely the precession force which is no longer perceived from outside a system containing two counterrotating flywheels. | |
| Oct 7, 2013 at 9:02 | comment | added | user1055643 | Not looking for X2 because 2 flywheels, or anything close to relativistic. I'm talking about how, when you have a single gyroscope, and you attempt to rotate it around an axis 90 degrees from its rotational axis, and you resist the precession force that occurs, you STILL find that it is as if you were trying to rotate something much more massive than the wheel. I am pretty sure that my counter-rotating assembly will show the same effect, without the precession force. But to date, no one has satisfactorily addressed this issue (as far as I have seen) | |
| Oct 7, 2013 at 5:18 | comment | added | Selene Routley | Out of interest: are there any uses of this kind of thing that seek lack of nett torque alone. I think the oppositely spinning propellors on some aeroplanes, the issue is to reduce the torque arising from drag, which is always there and not to reduce the force when making the pair "precess". | |
| Oct 5, 2013 at 17:15 | comment | added | dmckee --- ex-moderator kitten | Well, there is a relativistic correction: the whole assembly is effectively more massive than it was with the wheels at rest, but that enters at the level of $m(\omega r/c)^2$. An effect more likely to be detected is that the frame may flex slightly when you first begin turning the device: be sure to build it strong because otherwise you are constructing a bomb powered by the rotational kinetic energy of the wheels. | |
| Oct 5, 2013 at 16:43 | comment | added | gregsan | hmm doubt it. i forgot to add that since the flywheels are counter rotating, their angular momentum vectors cancel nicely. ie, the system has 0 angular momentum. it will still take more force to torque the whole bit as a system, but only because it has more mass. | |
| Oct 5, 2013 at 16:26 | comment | added | user1055643 | Thanks for the diagram! I agree as in my post that there will be no precessional forces, as they cancel each other out in the two wheels. My question is different -- I suspect that it will still require more force to rotate the entire assembly in orthogonal directions than it would take if the flywheels were at rest. I believe the flywheels' motion increases the angular inertia of the system overall, and I'm looking for some explanation of why that is or is not the case. | |
| Oct 5, 2013 at 9:36 | history | answered | gregsan | CC BY-SA 3.0 |