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Servo Controller Help

Harkinsny5

Jan 23, 2010
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Jan 23, 2010
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I'm not able to get this circuit to give me full range of motion of a servo (only about 90 degrees). Maybe someone can take a look at the circuit and let me know what I'm doing wrong. I put it together with pieces I had lying around which is why I'm using so many resistors to get the desired values. (It's not labeled but of course that is a 555 timer in the schematic).
 

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Resqueline

Jul 31, 2009
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Try one of those variable duty-cycle circuits with two diodes, one to each end of the pot to give separate charge/discharge paths. The adjustment should then keep the frequency more or less constant (at 50Hz) while the duty can be varied up to 10-90%.
 

Harkinsny5

Jan 23, 2010
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Jan 23, 2010
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So the variation in frequency (10 hz or so) would prevent the servo from obtaining full rotation?
 

Resqueline

Jul 31, 2009
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Only 10Hz variation might not be the problem but the simplicity of that design might impose some other restrictions. I'm not used to using the 555 so I'm not too aware of its possibilities & limitations.
Since R/C servos are supposed to have 1.5ms +/- 0.5ms (at 50Hz) for 90 +/- 90 degrees of rotation I'd try to replicate that.
Here's one example that seems to be accurate & thorougly designed.
 
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