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Weird servo problem.. Help?

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Old 01-23-2008, 06:52 PM
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av8tor1977
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Default Weird servo problem.. Help?

Hi,

Been building, flying, and crashing models for 35 years. I've never seen a problem like I have encountered with my most recent airplane.

Christen Eagle biplane, Futaba 7C radio and receiver, BP Hobbies high torque servos.

Aileron servos are on a "Y" connector.


When you move the aileron stick side to side normally, everything works fine. When you move the aileron stick full deflection to the right and release it, the servos immediately return to center as they should. However, when you move the aileron stick full deflection to the left and release it suddenly, the servos go past neutral to full deflection in the opposite direction, and then immediately go to neutral.

If you move the stick in a more normal fashion; letting it return to center more slowly, it doesn't do it. But if you release the stick and let it snap back to neutral, that's when the servos get weird and they go full opposite before coming back to center. It only does it with left stick deflection and sudden release. What could be causing this weird problem??

BTW, this transmitter works fine with other airplanes, and range checks fine with this airplane.

Help?
Thanks,
AV8TOR
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Old 01-23-2008, 07:06 PM
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Default RE: Weird servo problem.. Help?

Sure sounds like a bad transmitter stick pot to me.
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Old 01-23-2008, 07:21 PM
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av8tor1977
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Default RE: Weird servo problem.. Help?

Thanks for the response.

Yeah, one would think so, but the transmitter works fine with other airplanes.

Just to be absolutely sure, after reading your post I got out another airplane that is set up with that transmitter and tried it. It works fine. Then, as a further check, I switched modes on the transmitter and tried it on the Christen Eagle again. The problem moved to the rudder stick. So it can't be the transmitter.

As I said, it's a weird problem I've never encountered before!

AV8TOR
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Old 01-23-2008, 07:40 PM
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Default RE: Weird servo problem.. Help?

I had a similar situation where the ailerons would oscillate at the center position when quickly released and then stabilize. Sort of like they were connected by a spring instead of a solid connection to the servo. Thinking it might be a bad aileron servo, I replaced both of the servo extensions and both aileron servos with new ones and the problem went away. Who knows?
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Old 01-23-2008, 07:46 PM
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Default RE: Weird servo problem.. Help?

Here's one other trick.
Eliminate the "Y" cable from the aileron servos, then one at a time test them in the aileron port and see if the problem persists.
Flakey "Y" harnesses can do strange things.
If the "Y" harness is the culprit, have you considered using the dual aileron function on the radio??
Good luck,
Pete
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Old 01-23-2008, 08:11 PM
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av8tor1977
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Default RE: Weird servo problem.. Help?

Ok, thanks guys. I'll try isolating it some more. My workshop is in my office, so tomorrow when I go to work I will see if I have a servo extension I can use to eliminate the "Y" connector and test the servos one at a time.

Since they are on a common circuit with the "Y" connector, could one bad servo somehow send a feedback signal that would cause them both to have a problem? Also, have any of you had problems in general with BP Hobbies servos?

I wasn't going to run flaperons or other mixing functions, so I just used a "Y" connector on this one....

Thanks again,
AV8TOR
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Old 01-24-2008, 09:41 AM
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Rodney
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Default RE: Weird servo problem.. Help?

Most probably due to a poor connection somewhere in the loop. As stated above, try bypassing the Y connection with a second spare extension to each servo, one at a time. Dirty or poor connections will often cause this type of problem.
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Old 01-24-2008, 12:04 PM
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Default RE: Weird servo problem.. Help?

i stopped using y harnesses for that fact. i had two different planes with dual servos on a y harnes have a problem just like that. even had it happen on servo extensions. but after i went to a new extension or new y harness the problem went away.
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Old 01-24-2008, 10:19 PM
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Default RE: Weird servo problem.. Help?

Thanks for all the responses guys. I made up a servo extension today to test things out. It may be a day or two before I can get back to troubleshooting it, but I'll let you know what I find.

AV8TOR
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Old 01-25-2008, 03:50 PM
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Default RE: Weird servo problem.. Help?

Well, it was a bad servo. I tested it "every which way", and it is one of the new Bluebird "TowerPro" servos that is bad. So the answer is yes, if one servo is bad in a "Y" connected circuit, it can make the other servo do weird things. With a replacement servo now in place of the offending one, everything works perfectly.

I'm going to make another post asking everyone about these particular servos. I realize that with any brand servo one could get a bad one, so I just want to see if anyone else has had problems before I buy these servos again for the next project.

Thanks again,
AV8TOR
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Old 01-25-2008, 06:23 PM
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Default RE: Weird servo problem.. Help?


ORIGINAL: airbusdrvr

I had a similar situation where the ailerons would oscillate at the center position when quickly released and then stabilize. Sort of like they were connected by a spring instead of a solid connection to the servo. Thinking it might be a bad aileron servo, I replaced both of the servo extensions and both aileron servos with new ones and the problem went away. Who knows?
This is ironic. In my post above on this subject, it was Tower servos that I replaced with Hitec HS475s that solved the problem.
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Old 01-26-2008, 01:34 AM
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Default RE: Weird servo problem.. Help?

"TowerPro" is different from Tower Hobbies servos. Tower Hobbies servos are produced variously by Futaba and Hitec I believe. The TowerPro or "Bluebird" servos are made in China as I understand.

Ironically, I do have a Hitec 55 mini servo on an electric plane that is doing exactly as you described. I imagine it is a dirty or bad pot in the servo.

AV8TOR
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Old 01-26-2008, 11:15 AM
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Default RE: Weird servo problem.. Help?

Good to hear you have it sorted out[8D]
It's because of situations such as this that make me avoid "Y" harnessing two servos together at all costs, I use the flaperon mix on all my dual aileron setups, even though I'm not using them as flaperons or spoilerons, makes setting up differential throw a breeze
Good luck,
pete
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Old 01-26-2008, 11:27 AM
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Default RE: Weird servo problem.. Help?

Thanks. I spent an hour or so searching and reading other posts about these TowerPro servos. A few people have had luck with them, but the majority, and overall opinion seems to be "Stay away from them!" It was enough to convince me....

It's too bad, as I feel so many things are radically overpriced these days and it was good to find something at a low price! Being as that I have about 12 airplanes flying at the moment, and more projects coming, I use up a lot of servos!!

AV8TOR
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