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Servo bobble

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Old 08-11-2003, 01:17 PM
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John Wells
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Default Servo bobble

A friend has two standard S148 servos hooked together with a y-harness on the wing of a biplane. When the servos are moved either way, when they return to neutral, they go a bit past center and then return to center. The transmitter stick isn't moving the other way, but the servos both bobble a bit to the opposite direction before settling to neutral. Both do the same thing at the same time. Has anyone seen this and do you have any suggestions?

Thanks,

JW
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Old 08-11-2003, 01:42 PM
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Default Servo bobble

Have you tried 2 other servos with the same Y conection in the same plug on the rec? Do they do the same? Does just one do it without the Y connection? If so, you may have a bad pot in the trans, or something in the rec. See if others do it or if it does without the Y to make sure where the problem is. If they still do it, try a diff rec to see if it is the rec or trans. I would start there anyway.
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Old 08-11-2003, 04:11 PM
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John Wells
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Default Servo bobble

We'll check that out and replace the servos.

Thanks
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Old 08-13-2003, 04:48 PM
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Dave McDonald
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Default Servo bobble

JW,
If the servos are oscillating quickly.....like a buzz......then the servos may be suspect, or the transmitter stick pot may have a problem.

But if the servos are oscillating slower.....like a swinging door......then I'm guessing you're using a Hobbico Y-harness......which is the culprit. The standard Hobbico extensions develop high resistance connections, which causes a severe voltage drop to the servo under load. Another test is to push against the control surface. If it's a bad Y-harness, then it won't take much force at all to overpower the servo and deflect the control surface. Replace it with a higher quality y-harness and the problem will disappear.
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Old 08-14-2003, 04:50 AM
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Lynx
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Default Servo bobble

Always use high gage wire for Y harness's. Or any other wireing for that matter. Unless you're into super micro planes there's no reason not to use wire that's 2-4 gages higher than what you 'need' It makes sure the wire is almost never at fault, and reduces power lost in heating thinner wire.
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Old 08-14-2003, 07:38 PM
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John Wells
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Default Servo bobble

Thanks all, we are going to check the Yharness and wire guage.

JW
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Old 08-14-2003, 07:53 PM
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Default Servo bobble

It it is happening to both servos, check the connector that plugs into the receiver first. I just isolated a similar problem on my 60 sized Ultra Stick (long leads) and in turned out to be the connection between the servo and the servo extension.

You may find by inserting the connector from the Y cable a bit more into the receiver your problem will go away. Those Hobbico connectors sometimes fit a bit tight, and you may not have them plugged in all the way (you know how I know!).
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