Author Topic: Servo jitter, removed by buffer  (Read 4130 times)

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Offline octagonxTopic starter

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Servo jitter, removed by buffer
« on: September 05, 2007, 11:39:44 AM »
I just want to share how we solved servo jitters

We were having problems controlling 12 servos for our quadruped robot using one microcontroller and 6V battery.  Everytime a leg moves, the servos jitter.  We tried the solutions posted here, like twisting wires etc, but none seem to remove the problem.  We then tried using 74LS245 buffer from the microcontroller to the servo.  Until now, the vibrations has not yet returned.  I think, adding buffers to the signal greatly removes unwanted signals from coming in...

Offline HDL_CinC_Dragon

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Re: Servo jitter, removed by buffer
« Reply #1 on: September 05, 2007, 03:10:27 PM »
From what it sounds like, if you had just placed a 1uF capacitor between GND and VCC(I think, I could be mistaken on location there...) it should have filtered out the unwanted signals... I MIGHT be wrong about this though...

You should post more too just for reference. For instance, what setup did you use and what other methods had you tried and such... just a thought :)

Thanks for posting a work solution!
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Offline Admin

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Re: Servo jitter, removed by buffer
« Reply #2 on: September 06, 2007, 01:11:11 PM »
did you try this? (it was one of the suggestions on this site, and the one I use :P)
http://www.servocity.com/html/boosted_servo_extensions.html

HDL_CinC_Dragon, your suggestion wouldnt work :P
The problem is in the signal line, not power lines.

Offline octagonxTopic starter

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Re: Servo jitter, removed by buffer
« Reply #3 on: September 08, 2007, 12:44:09 AM »
I think the idea is the same.  But we tried displaying the input signal using oscilloscope, and the 3.3V output of the microcontroller doesn't seem to be degraded.  What really happens is that, each time another servo moves, the ground (0V) level of the input signal becomes too noisy.  That's what I think causes jitters, because the servo seems to interpret that noise as a control signal.  Also, what we do is that we placed the buffer just after the microcontroller, unlike the buffer-booster placed midway at the servo wires.  Isn't it that buffer only reduces loading effect?  Does it also blocks noises from coming in?

Anyway, the buffer works.  We hope the jitters won't come back, because the presentation will be 2weeks from now.

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Re: Servo jitter, removed by buffer
« Reply #4 on: September 08, 2007, 07:14:15 AM »
Hmmmm well if ground shifts, then technically the signal line does too - the real signal voltage is signal minus ground.

In this case, I think HDL_CinC_Dragon's suggestion of adding a cap would have worked.

Offline HDL_CinC_Dragon

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Re: Servo jitter, removed by buffer
« Reply #5 on: September 08, 2007, 08:02:33 AM »
Hmmmm well if ground shifts, then technically the signal line does too - the real signal voltage is signal minus ground.

In this case, I think HDL_CinC_Dragon's suggestion of adding a cap would have worked.

Score one for teh Dragon!

Ill take my leave now :)
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