Loosely held rotating object tendency to stay with CG
Loosely held rotating object tendency to stay with CG
(OP)
I am trying to think about this scenario, but not sure what to think. Let's say you have a loosely held (low friction) disk object held between two clamps and spinning on a hub at a certain RPM. As the disk-shaped object is spinning, it is perfectly balanced on its X-Y CG. Does the rotating disk have a tendency to remain balanced with a rotational inertial force (ignoring friction)? If so, how would I calculate what the "self-balancing" force would be?





RE: Loosely held rotating object tendency to stay with CG
I can't figure out what your question means ... could you paraphrase it?
RE: Loosely held rotating object tendency to stay with CG
RE: Loosely held rotating object tendency to stay with CG
what you describe might be called a "metastable" state in electronics. Any minor perturbation will unbalance the system, and it will get progressively worse, since there is no compensating force.
TTFN

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RE: Loosely held rotating object tendency to stay with CG
The axis of rotation for the disk is fixed by say a rotating motor hub, and the disk is loosely held by a top and bottom clamp. The motor hub rotating axis is parallel with gravity.
Thanks TheTick, I was thinking of gyroscopes, but still not sure how to apply the concept to the scenario I described.
RE: Loosely held rotating object tendency to stay with CG
I shall await erudite answers.
I suspect damping has something to do with it.
Cheers
Greg Locock
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RE: Loosely held rotating object tendency to stay with CG
http://www.youtube.com/watch?v=hW57tLMcqt4
RE: Loosely held rotating object tendency to stay with CG
There is rotational inertia, but no active force.
TTFN

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RE: Loosely held rotating object tendency to stay with CG
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Loosely held rotating object tendency to stay with CG
RE: Loosely held rotating object tendency to stay with CG
RE: Loosely held rotating object tendency to stay with CG
Imagine a uniform disc lying on an ice rink. using a speedo drive, apply a torque about the vertical axis.
The point of application of the torque doesn't matter, the disc will spin up around the cg, as no translational force is applied.
Now clamp it to earth via a vertical axis bearing, again through the cg.
Apply torque, same result.
Now move the axis of the bearing to the rim of the disc. The disc rotates around the bearing, a large rotating restraining force vector is generated in the bearing. Now release the bearing, and the disc will shoot off in its last tangential direction, still rotating.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Loosely held rotating object tendency to stay with CG
RE: Loosely held rotating object tendency to stay with CG
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Loosely held rotating object tendency to stay with CG
They do tend to be self balancing but it doesn't take much to unbalance them.
The big ones are tensioned and they lose tension with use so they tend to fold over and are thus sort of self unbalancing.
Maybe how much unbalancing (and recovery) gets done by how much force such s knows in logs, loose collars, bumps in a shaft, machine vibration, etc.
Thomas J. Walz
Carbide Processors, Inc.
www.carbideprocessors.com
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