Servo, Rx or Tx problem? - RC Groups
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Jun 20, 2007, 12:33 AM
Registered User

Servo, Rx or Tx problem?

My Formosa exhibits the strangest problem and I am not sure what the problem is exactly--hoping that some of you can help.

Three times now, I have completely lost elevator control for only a short period of time (5 seconds)--all other controls responded, except elevator, so I am assuming it is not a glitch.

All linkages are tight. The elevator always works on the ground. Electrical connections seem to be good.

I've been lucky that I've been level when the problem occured, but I'm a bit hestitant to fly again until I know it's solved.

Can a servo fail like this?

Can an Rx fail intermittently on one channel?

Can the problem be in the Tx?

Futaba 4 Channel Skysport.
GWS Naro Rx.
Hitec 55 servos.
3S lipo, Towerpro ESC and BP21 motor, should that matter.

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Jun 20, 2007, 02:00 AM
Deletedfor proving Nauga wrong
yes a servo can fail like that. Its not common, but if the signal lead is intermittant then the servo can just stop responding.

5 seconds of loss of elevator is too long to tollerate. Find the cause before flying the plane again. I would start by replacing the servo and any extension that might be in between it and the RX.

The TX would not be likely to be the problem. A failed potentiometer would drive the affected channel out AND every channel affterwards in sequence would be expected to go wild.

Pretty easy to be demonstrate that.... take an old junk TX and purposefully disconnect the center wire from the elevator or aileron pot at the gimbal. turn the radio on (TX and RX) and touch the wire back... watch how the controls respond. (best to use old servos it can drive them past their design travel range.)

I'd bet on a bad servo or a bad receiver. (bad solder joint at one of the pins to that servo if its the receiver)
Jun 20, 2007, 02:23 AM
Baptised Heathen
batman's Avatar
I had the same thing happen to me with brand new servos on all controls. Turned out the rudder servo was faulty and it was a brand name servo. It has a bad connection to the printed circuit board which I managed to resolder and then no problems.
Jun 20, 2007, 04:33 AM
An itch?. Scratch build.
eflightray's Avatar
Time Pilot

Try swapping the rudder and elevator servos over. If the servo is at fault it's safer to have it on the rudder than elevator.

If the fault still occurs on the elevator, at least you've eliminated the servo as the problem.
Jun 20, 2007, 10:49 AM
Oldie but goodie
Popsflyer's Avatar
I had a Receiver (Hitec Feather) that would cut throttle and apply FULL down elevator when it glitched. Caused alot of crashes before I figured it out.

Could the GWS nano RX be the problem?
Jun 20, 2007, 04:50 PM
Deletedfor proving Nauga wrong
Note... the GWS 4P RX's I bought (years ago...) had an issue with the insulation slipping off the antenna lead. Replacing the antenna with a better grade of wire cured a lot of strange issues that occurred when the original wire (exposed by slipping inslation) shorted the back side of the RX circuit board.

No problems with the little cheap RX's since antenna replacement.
Jun 20, 2007, 05:11 PM
Panda Panda Panda Panda Panda
rdwoebke's Avatar
Another possibility. Open up that elevator servo. I had a situation once where there was a broken gear tooth on a servo and sometimes it would cause the servo to "stick". Normally it would be OK, but after say full down elevator it would stick.

Jun 21, 2007, 01:11 AM
Registered User
What a great community--all the quick replies!

I won't be able to look into the problem until the weekend, but I still want to thank you all for the great ideas, gentlemen. Very much appreciated.

Once all repairs are done, I will post how it went.
Jun 21, 2007, 01:38 AM
Registered User
I would replace the servo and see how it goes. If it still doesnt work then im not sure what the problem is. Sorry!

Jun 21, 2007, 10:05 AM
Oldie but goodie
Popsflyer's Avatar
You should be able to reproduce servo problems on the ground, but a Glitchy RX might not show up unless at range.
Jun 22, 2007, 03:51 AM
Registered User
Originally Posted by Popsracer
You should be able to reproduce servo problems on the ground, but a Glitchy RX might not show up unless at range.
The plane wasn't far away when the elevator locked up, at most 100 feet, and I still had function of the other channels. Plane range checks fine on the ground, so it's either the servo or that one channel that's defective.

I'm not too fond of these kind of problems. I just wish whatever was not working would completely fail so I'd not have to wonder.

Oh, forgot to add that I tested the current draw of the elevator servo and found it normal.

My plan is to test the servo while wiggling the wires going in to the Rx.

If that turns up nothing, I'll replace the servo and hope that was it.
Jun 22, 2007, 09:56 AM
Oldie but goodie
Popsflyer's Avatar
Good luck, hope you find the problem. Glitch troubleshooting can be maddening sometimes.

Let us know if you find anything.
Jun 25, 2007, 02:48 AM
Registered User
I replaced the servo today and flew for about an hour today without any issue. The problem before was intermittent, so I'm hoping that took care of the problem.

Thanks again for all the replies, gentlemen!

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