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4hv.org :: Forums :: General Science and Electronics
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Using R/C servo signal to drive dc motor?
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waffle
Sun Dec 02 2007, 04:39AM Print
waffle Registered Member #642 Joined: Fri Apr 13 2007, 10:19PM
Location:
Posts: 15
 		Does anyone know of a way to take the PWM servo signal from a remote controlled car receiver and somehow turn it into a variable resistance signal? The reason I'm asking is That I'm trying to drive a motor controller that uses a potentiometer input to vary speed. Thanks.
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...
Sun Dec 02 2007, 05:25AM
... Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
 		Well, the easiest thing would be to simply hook a servo into a pot...
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Electroholic
Sun Dec 02 2007, 06:36AM
Electroholic Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720
 		Link2

or you can take apart a servo, replace the internal pot with a resistive divider(2.7k+2.7k iirc), and now you have a motor controller.
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Steve Conner
Sun Dec 02 2007, 12:55PM
Steve Conner Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
 		There's no such thing as a "resistance signal": it will be either a voltage or a current.

The Robot Wars guys make little boards with PICs and optocouplers on them, to convert from RC servo signals to the pot input of a larger controller. I have some Team Delta boards kicking around from my own failed Robot Wars attempt years ago. :P
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Dalus
Sun Dec 02 2007, 01:01PM
Dalus Registered Member #639 Joined: Wed Apr 11 2007, 09:09PM
Location: The Netherlands, Herkenbosch
Posts: 512
 		You just need a pwm to DC convertor
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Avalanche
Sun Dec 02 2007, 01:37PM
Avalanche Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845
 		well, think what the pot could be doing in the motor speed controller - it most likely set up as a potential divider that creates a variable voltage to set your motor speed (assuming some kind of PWM motor controller). So what you really need is voltage signal. You make this by filtering the PWM output, and with the right filter you will get a DC level that is relative to the pulse width, and this is what you would hook to the controller. The simplest filter might be a 10k resistor with a 10n cap to ground, take the signal from the cap side of the resistor.

There are a few unknowns though, so just take this as a possible approach rather than a working solution.


i.e. The pot could be doing something completely different tongue
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ConKbot of Doom
Sun Dec 02 2007, 03:27PM
ConKbot of Doom Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
Location:
Posts: 329
 		you could take the easy way out and buy a speed controller that takes servo style PWM in
Link2
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Electroholic
Sun Dec 02 2007, 07:46PM
Electroholic Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720
 		yes, most pots for motor controllers are set up as voltage divider, and a variable voltage signal will work. Problem is that most servo signals have a ~18ms period, and on time varies from 1ms to 2ms, unless you add opamps, its probably not going to work.
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cjk2
Sun Dec 02 2007, 10:31PM
cjk2 Registered Member #51 Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263
 		I have done this with an ateml tiny2313 before. If you are really interested in this, let me know and i can give you some code and a pcb layout for a 2.4a dual motor controller.
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