Subject:
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Re: Using the Motor as a Tachometer
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Newsgroups:
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lugnet.robotics
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Date:
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Mon, 9 Aug 1999 21:48:15 GMT
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Viewed:
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930 times
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In lugnet.robotics, dbaum@spambgoneenteract.com (Dave Baum) writes:
> I'm not a EE, but here's my take on the situation...
>
> Turning the motor increases the electrical potential (voltage) between its
> two contacts. If the motor isn't connected to anything, then its easy to
> turn - relatively little energy is required to make one of the motor
> contacts sit at a higher potential than the other. If you short the motor
> contacts together, however, then you have a different situation. In order
> to maintain a difference in potential, you need a sizeable current moving
> through the wires. This requires a lot of work, thus its hard to turn the
> motor. Thus how "hard" it is to turn the first motor has to due with how
> much current needs to be moved in order to maintain a certain voltage.
>
> At 9V, the incadescent lights will draw more current than the motor. My
> rough measurements are about 30ma for the light, and less than 5ma for the
> motor (free running). This doesn't directly relate to efficiency. Just
> becasue one device draws more power than another, that doesn't necessarily
> mean it is any less efficient. For example, a large switching power
> supply will draw much more power than a small linear regulator, but the
> switcher is almost certainly more efficient.
>
> One reason the motor draws so little energy when running without a load is
> that it hardly needs any energy to keep spinning. This doesn't
> necessarily mean it is efficient at converting electrical to mechanical
> energy. Its just efficient at not losing its present mechanical energy
> (angular momentum of the flywheel) due to friction, etc.
A-HA!!! That makes sense!
> To judge efficiency, we would need to quantify how much of the energe
> going into the light is emitted as visible light. And for the motor we
> would need to measure the amount of mechanical energy it produced.
> p.s. Probably a much longer answer than you were looking for, Todd.
No, this is great!!! Thanks!
--Todd
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Message is in Reply To:
 | | Re: Using the Motor as a Tachometer
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| (...) I'm not a EE, but here's my take on the situation... Turning the motor increases the electrical potential (voltage) between its two contacts. If the motor isn't connected to anything, then its easy to turn - relatively little energy is (...) (25 years ago, 9-Aug-99, to lugnet.robotics)
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