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 13:31:34 GMT
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Viewed:
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1003 times
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> > One funny thing I noticed: I had to apply about twice as much torque to
> > turn the wheel with the lamp attached to the motor as I did when the motor
> > was hooked instead to a second motor. That is, it "felt" about twice as
> > hard to turn the wheel at the same speed. Is this because the lamp is
> > super-inefficient at converting electomagnetic energy to visible light,
> > while a LEGO motor is super-efficient at converting electromagnetic energy
> > back into kinetic energy?
>
> 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.
In fact, this is how the RCX motor controller internally sets the motor up
for "brake" instead of "off"...
Cheers,
Ralph Hempel - P.Eng
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Outside of a dog, a book is a man's best friend.
Indside of a dog, it's too dark to read...
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Reply to: rhempel at bmts dot com
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Message has 2 Replies:
 | | Re: Using the Motor as a Tachometer
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| In fact, if you hook up two motors using the black cords and turn one of them, the increased voltage will cause the other one to turn without any physical effort applied to it. That's pretty rad. I'm not sure if I understand the brake concept? Could (...) (25 years ago, 9-Aug-99, to lugnet.robotics)
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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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