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Centered servo current drain

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Old 07-28-2004, 09:29 PM
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Keefer
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Default Centered servo current drain

I've followed some really great posts on current draw with servos under load, but I found only one that discussed servo drain while centered.

I'm trying to track down a problem, so I'm measuring current draw on a 4.8v NiCd 1600 mah and pulling one servo lead from the Rx at a time. Most only show about a 10 ma draw (if that), but one shows nearly 130 mah draw under no load. It's not jittering, but if I jog it in one direction, it seems to find it's center and drops down to about 10. Jog it in the other and I'm up to 130 ma - centered - no jitters.

I think this is why my 1600 mah pack is only lasting about 10 minutes!

This servo's set up on a pull-pull - would a little bit of drag or too-tight wires cause this?

Thanks, all

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Old 07-28-2004, 09:52 PM
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Geistware
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Default RE: Centered servo current drain

I don't think this is it.
10 minutes on a 1600maH pack is about 6 amps of current.
Do you use this on an electric motor?
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Old 07-28-2004, 10:06 PM
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Default RE: Centered servo current drain

Sounds like to me you have some drag or friction in the linkage for the subject servo.

If it cannot center, or nullify at the center, then it's going to draw some current attempting to get there.

If the drag on the control surface is too much for it to overcome then it's just going to stop(stall) someplace short of center and draw a finite amount of current trying to get there depending on the drag, or friction. It will never get there of course because there's too much friction.

The above is true only observing the airplane statically. The subject control surface will seek nullification in flight due to the fact that the airflow over the control surface will overcome the static resistance in the linkage/hinge mechanics.

One should always apply common sense when observing these things. You should always try to interpret the response as the airplane flies rather than while at rest on the ground. You'll save yourself a lot of unnecessary anxiety.....

That's generally what happens in this situation.
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Old 07-29-2004, 09:53 AM
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Keefer
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Default RE: Centered servo current drain

Yup, drag was the problem - one of the two pull-pull cables was not clearing a wing spar properly (the servo's buried in the wing of a profile plane), and was cutting into the balsa. I cleared the interference which helped significantly.

I discovered that the LED battery voltage indicator covers 4.5 to about 5.3v, so within 10 minutes I was down to 4.9v, which is actually fine. My other voltage indicators stay up near the top of the scale longer.
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