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Speed measurement via string

Hi

A non-flexible string is attached to an inertia at one end and the other end is wound on a spool. The inertia accelerates and then decelrates and its instantaneous velocity is required to be measured by watching a tacho meter connected to the spool.

My question is that in "no-slippage" condition if the inertia decelerates after initial acceleration during traversing what will happen to the tension in the wire. The worry is whether the string would get sag thereby failing to turn the spool and not providing the read out of its instantaneous speed during deceleration process.

Thanks

RJ Khan

Reply to
rjkhan
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Dear rjkhan:

Not good for high speeds.

Not believable with a real spool, with multiple layers of "string". Layers will "pack" down into one another.

It will be all over the place. "Pay out" of the wire will have it jumping over lower wraps after just a few cycles. As the OD changes (each layer is at a different diameter, and will result in a different angular speed), the string will "pulse".

Yes. A better term might be "deform" as in deformable solid.

The spool should be powered, either by a constant torque motor, or a spring. Because the string won't wrap all by itself.

That won't happen anyway. You might be close, but not terribly.

There should be a lot of performance history on this design. A similar device is used as cheap feedback in rocketry: "string pot". You might want to do a Google search.

David A. Smith

Reply to
N:dlzc D:aol T:com (dlzc)

snip

goes up by F=ma ( + friction if the mass sliding on a surface)

a non-flexible string does not sag -

they do not exist, either.

Reply to
Hobdbcgv

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