EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: schembri_andrew on September 15, 2014, 04:33:00 am
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Hi!
I have an rc receiver, and would like to use it to switch a dc motor (either on and off without the proportional speed contro.. Maybe extent to reverse with an h bridge later on). How could i go about converting the high and low pulse width from the reveiver to an on and off state? I read about controlling a servo and use it to push a microswitch at its extremity which in turn switches a relay but i would prefer a solid state switching method.
I found rc switches for sale but where is the fun in that? :clap:
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Average the pulse into DC with an RC filter, feed into a comparator and have it drive a switching element e.g. an NPN for turn on or off your motor, you exceed the threshold and its on, fall beneath it and its off,
only consideration may be using a resistor to add some hysteresis so you have to decrease a bit before it turns back off to prevent any risk of oscillation
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One of the complications is that the classic R/C control system uses pulse width to specify the servo/throttle position, but says nothing of pulse rate. So you might be able to use a simple R-C filter to get a DC value and feed this to a comparator and tweak it until it works, but the moment that the pulse rate changes, it will stop working. You need a circuit where the pulse width is measured and the pulse rate won't matter. Pulse width of 1 ms is full one left, and 2 ms is full right, with 1.5 ms being centered. (left/right are relative). Did you Google? (http://lmgtfy.com/?q=R%2FC+on%2Foff+motor+control+diy). Lots of information there.
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The old PWM radio control systems I have played with had constant off time with variable pulse widths so the on time for the other channels would affect the off time for any one channel.
I would integrate the pulse width and reset the integrator during the off time. Then if the output from the integrator is high enough, trigger a retriggerable monostable multivibrator which activates the motor driver.