Quote:
Originally posted by rust710
I have a servo that will not go to it's full range. ie 0 should be all the way to the left but it will only go to a forth of the way there from center but it goes all the way on the other side. Is there a way to calibrate a servo?
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You can't calibrate the old fashioned PWM style RC servo. The very expensive "DIGITAL" servos you can calibrate, but they're still fairly new devices.
To work, standard PWM RC servos require a 5V positive going pulse, with a pulse width of roughly 1.0ms - 2.0ms, repeated at about 50 Hz. The pulsewidth encodes the "target" position. 1.0ms = full one way, 1.5ms = the "center" position, and 2.0ms = full the other way. The circuit board inside the servo compares the incoming pulse against one it generates itself based on its feedback pot. If they're different, the difference is stretched out and drives the motor the right way, creating a little "jerk" toward the target position. That's why you need to keep refreshing the servo with pulses, to "walk it" to where you wish it to be, and KEEP it in position against any backdrive forces.
There's nothing to calibrate in this system. Electrical parts COULD go bad, but that's rare. Most of the time either your mechanics fail, the driver transistors burn out, or the pot gets munged up, but I've yet to see the timing circuit screw up from a bad capacitor. The timer is a single IC.
The pot inside the servo CAN go bad, which COULD cause your symptoms, but it is MORE likely a problem with your transmitter CONTROL'S calibration, and not the servo itself.
Try this: Disconnect anything attached to your servo (to eliminate any "mechanical stops" from the thing you're driving). Now if your servo doesn't run the full travel, check your transmitter. They often have trim pots either beside the sticks, or under a cover somewhere (often on the back, or under a label plate) for setting a servo's "travel range" and "offset".
If you wish to test beyond that, here's Ahmet Onat's page on how servos work, including a cute little 555 based tester box you can build to check out servos:
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http://www.geocities.com/BourbonStre...rvobasics.html
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BTW... BE CAREFUL with Onat's wiring of the servo! The RED is the +5v, the BLACK is the Ground, and the OTHER COLOR (typically white or orange) is the PWM Signal lead that connects to the transistor, as is shown in the schematic.
However, in OUR servos, the white is on one EDGE, and is NOT the middle conductor! The wire ORDER for OUR servos is normally Orange/White(Signal), THEN Red(+5v), THEN Black(Ground), which is DIFFERENT than that schematic!
For more information, see this thread, called "Pwm":
http://www.chiefdelphi.com/forums/sh...ighlight=servo
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Good luck, and Happy Holidays!
- Keith