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Help: brushless motor speed control

Old 04-12-2010, 09:07 AM
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pranav0091
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Default Help: brushless motor speed control

Hi,
I'm working on a project involving brushless dc motor. However unlike in the case of RC airplanes, I do not have/need an RC Tx-Rx module.
My problem is that I don't know the waveform that the Rx module supplies to the BEC. I would like to make the motor run at a constant speed.

I understand that, in general, the signal will be time varying as one has to control the speed of the motor, but my question is-
Is the waveform a slowl time varying voltage, with the motor speed being proportional to the instantaneous voltage?
or
Is the signal a periodic wave, whose frequency/duty cycle controls the motor speed?

I'm stuck at this point in my design, and really don't want to buy a RC module just to check the waveforms.

Any help is appreciated.
Thanks.
Old 04-12-2010, 10:04 AM
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whitecrest
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Default RE: Help: brushless motor speed control

Welcome to the forum!

I believe you are looking for a [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXVK79&P=7]servo tester.[/link] The technical description at the bottom of the page should clarify the issue. You won't need a Tx or Rx to set your motor to a constant speed.

Good luck with your project!
Old 04-12-2010, 11:25 AM
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pranav0091
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Default RE: Help: brushless motor speed control

Looks like it will serve my purpose.

Thanks a lot Tim. I really appreciate your help.
Old 04-12-2010, 11:37 AM
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pranav0091
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Default RE: Help: brushless motor speed control

I had seen a post in this forum by a user who had an issue similar to mine. Here's some data I found on the net-

The signal to a servo motor is a pulse width modulated waveform, with a time period of about 20ms and an ON time varying from 1ms(off) to 2ms (on).
the signal amplitude can be anywhere between 3 to 6 V, though 4.7V is more commonly used.

Remember this is the signal to be fed directly to the servo motor.

This information has not been verified by me.

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