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Strange problem with oscillating wing servo

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Old 07-31-2014, 06:42 PM
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sportflyer-RCU
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Default Strange problem with oscillating wing servo

I am trying to figure out what's causing the bottom left wing servo to oscillate by itself or overshoot at neutral .

Here's the scenario:

Its a new Electric Reactor biplane with all new servos . Receiver is Optima 7. Battery is A123 with a regulator set to 5.9V. Also has a 3 axix Gyro installed .

Maiden flight went perfectly , flies like on rails , no trim adjustment . The 3 axis Gyro was bypassed for maiden flight.

When powering up for the 2nd flight , the bottom left aileron went berserk ...ie starts to oscillate by itself. However the top left aileron which is connected in Parallel with the bottom aileron ( Y connection) was perfectly still .

I could not find the problem at the field so I disconnected everything and brought it home for analysis .

Upon powering up again at home, the problem servo did not oscillate by itself anymore rather it behaved like it had a dirty pot ie at center there is a tendency to overshoot neutral position . I reduced regulator output to 5.1V problem was lessened but still there.

I then removed the 3 axix gyro completely and re connected the servos like normal but the overshoot problem still persists.

I left it overnight .

The next day , the problem went away . No matter what I tried , leaving radio on , moving sticks etc . the problem servo behaved perfectly. Now I am really puzzled .

So I assembled all the wings like I was preparing for flight . Turned it on and it was perfect. One last thing , I installed the motor battery and started the motor . With motor running at various power points I moved the TX sticks etc for 5 mins and the left bottom wing servo was behaving perfectly. So I powered down , removed the motor battery. After waiting for a few minutes , I turned on the TX and RX. .......Guess what ....the problem servo started to overshoot again at neutral position !

Now I am beginning to suspect a receiver /servo combo temperature problem. The receiver is running warm to the touch . When its cool , the problem is fine but when the internal temp gets warm after a run , the left bottom servo starts to exhibit overshoot but why not the other parallel servo or the right wing servos?

I think the fuselage internal could get a bit warm because the heat generated by the ESC ( mounted up front with the motor) plus motor battery and the voltage regulator is being channeled through the firewall, through the fuselage and exhausted through a cut out at the fuselage bottom behind the bottom wing . I am wondering whether this could be the cause of the problem because after flying there is no more airflow and the heat builds up in the fuse?

I see 3 possible ways toget to the bottom of this frustrating problem :

a) Cut a large hole at the cowl bottom to reduce heat going thru fuselage ( the original design did not have any opening in the cowl except for intakes)

b) Replace the problem servo

c) Replace the receiver .

Any other suggestion as to the cause of this problem and what to do next to solve?

Thanks
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Old 07-31-2014, 07:44 PM
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JohnBuckner
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Hmm, replace the 'Y' cord and/or any other extensions you may have connected to that 'Y' cord.

John
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Old 07-31-2014, 08:31 PM
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l already replaced the Y cords . No luck there.

I decided to go ahead and replace the Optima 7 receiver with a spare Optima 9 I had lying around. That seemed to fix the problem. I had to do some fiddling around to locate the dual antennas.

I will run the motor tomorrow to generate heat in the fuselage and see what happens . If it fixes the problem , then the Optima 7 is the first receiver I have with a thermal problem .
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Old 08-01-2014, 06:07 AM
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Rodney
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Most probably the cause was (is) a bad connection between the receiver and servo which was corrected when you unplugged and replugged the servo connections. Extension cords are famous for causing such problems.
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Old 08-01-2014, 06:20 AM
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Originally Posted by Rodney View Post
Most probably the cause was (is) a bad connection between the receiver and servo which was corrected when you unplugged and replugged the servo connections. Extension cords are famous for causing such problems.
Does not seem to be so. I disconnected and reconnected Y's several times to no avail. The problem seems to be solved by replacing the receiver. I will confirm after a full dry run today. Ambient temps in the low 90's .
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Old 08-01-2014, 10:33 AM
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I trust you are not wrapping the receiver in a blanket that so many formerly did. That was one of the first things I learned to do was mounting receivers fully exposed on velro when I made the changeover to 2.4.

Was just down to the river a few days ago float flying and it reached 114 but no receiver heat problems. With any of the airplanes.

John
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Old 08-01-2014, 11:17 AM
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Remember on a y harness servos the misbehaving servo may not be the bad servo. It maybe the opposite servo on the Y
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Old 08-01-2014, 12:05 PM
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Originally Posted by jetmech05 View Post
Remember on a y harness servos the misbehaving servo may not be the bad servo. It maybe the opposite servo on the Y
Good point. The only way to check is to connect one servo at a time.


The bad news is that the servo oscillates again even with new receiver .

I got so frustrated , I replaced the A123 battery and the regulator with a good old 4 cell NiMH battery.

Now everything works perfectly even with motor running , waiting for heat build up etc. It just works like its supposed to .

Now I am not sure whether the problem is with the Linear regulator or the A123 cell. I would expect that all servos would be affected if its a battery or regulator problem.

Totally confused .
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Old 08-01-2014, 01:25 PM
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Have you tried changing the servo?

Servo problem change the servo Occam's razor.
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Old 08-01-2014, 02:07 PM
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I had a similar problem last year with a Escapade. When first powered up for the day one servo, for ailerons Y connected, would waive at me and stop. Move the ailerons and one would waive at me and stop. Oddly enough when I started the engine it would go away. It never failed when engine was running. I flew it for months that way.
I ultimately replaced the Y with a better quality one from Taildragger RC and problem was fixed.
Its really best to avoid Y cables whenever possible as todays servos and/or receivers don't seem to like them much. I don't ever recall Y problems back in the 80s and 90s.
Don't know why you are using a regulator with a A123 battery unless your receiver requires it.
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Old 08-01-2014, 09:32 PM
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I used a regulator because I was afraid that the S9202 servo would not accept voltages higher than 6V . I am going to try a LIFE 2100mah battery tomorrow instead of the 4 cell pack .

I can eliminate the two Y connection by using 4 channels for the 4 ail servos. I could not do that when I had the 7 receiver but obviously I can do it now that I have a 9 ch receiver installed.
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Old 08-02-2014, 10:21 AM
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I had what seemed to be the very same problem with one of the elevator servos on a 100cc Extra 260. Every time I would exercise the servos, one side would overshoot and oscillate for about two or three times and then dampen to the proper position. I was using two channels. I tried a Y and everything that you have. Nothing seemed to fix the problem. But - the problem went away. And never came back. I never did figure it out.
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Old 08-03-2014, 09:50 AM
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Also try and replace the switch to the aircraft system
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Old 08-03-2014, 07:58 PM
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I switched to a LIFE battery and bypassed the RX switch but to no avail. However I started to notice that with the bottom wing not attached to the fuselage ( ie just lying on the table below the fuselage the servo did not oscillate ) . However when the bottom wing was attached to the fuselage , the servo sometimes would oscillate . This was quite perplexing. I decided to replace the short but rather thin servo extension lead from the receiver to the wing with a thicker, twisted servo extension lead. The problem seems to have gone away . I will test it several times during the day tomorrow to verify. Can a thin short servo extension lead cause all this headache? Poor contact , rf interference ?? Strange.
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Old 08-03-2014, 08:15 PM
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I thought you were using a "Y" cable for your ailerons. Are you also using an extension cable in addition to the Y cable?

FYI: A123 is a Life battery, A123 is a brand name though sold from different companys, so you had already tried a Life battery.
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Old 08-04-2014, 03:43 AM
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[QUOTE=sportflyer-RCU;11854191 Can a thin short servo extension lead cause all this headache? Poor contact , rf interference ?? Strange.[/QUOTE]

Yes to all the above and so can an excessive number of plugs from stacked short extensions and 'Y' cords. By the way the twisted heavy gauge servo wire is what I keep in bulk for all my extension needs but do not use stock extensions instead solder into the new servos cut lead with a custom length as necessary.


John
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Old 08-04-2014, 04:25 AM
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Originally Posted by sportflyer-RCU View Post
I switched to a LIFE battery and bypassed the RX switch but to no avail. However I started to notice that with the bottom wing not attached to the fuselage ( ie just lying on the table below the fuselage the servo did not oscillate ) . However when the bottom wing was attached to the fuselage , the servo sometimes would oscillate . This was quite perplexing. I decided to replace the short but rather thin servo extension lead from the receiver to the wing with a thicker, twisted servo extension lead. The problem seems to have gone away . I will test it several times during the day tomorrow to verify. Can a thin short servo extension lead cause all this headache? Poor contact , rf interference ?? Strange.
Like I said in post #4 above, most probable cause a bad connection or dirty/poor connector contacts.
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Old 08-04-2014, 08:08 PM
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Classic illustration of a bad pots on the servo. Nothing else. Get a new servo. Most pattern pilots from the 1980-90's experienced this many times.

Kurt
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Old 08-05-2014, 03:40 PM
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Originally Posted by Bozarth View Post
Classic illustration of a bad pots on the servo. Nothing else. Get a new servo. Most pattern pilots from the 1980-90's experienced this many times.

Kurt
I can't count how many times I have seen this problem and every time the anwer was exactly what Rodney's #4 post explained. I spent many an hour cleaning pots back "in the day" but dirty or poor connections are more than likely the problem. There is a wide variety of aftermarket extensions and Y harnesses. Yes they will plug into each other but the actual metal parts that transfer electricity may not be good fit electrically. . Next time it happens with the radio still on grab the surface and try to move it, you will be able to with very little effort cause of the low power making it to the servo..
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Old 08-05-2014, 04:25 PM
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Hey pkoury,

I have never once had an issue with dirty or poor connections. Not once. I guess I have been lucky.

Kurt
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Old 08-05-2014, 06:24 PM
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Guys,

The original Aileron configuration : 7 Channel receiver.

Both Wings have one servo extension lead from servo to center of wing , nothing unusual here.

Top and Bottom Left Wing aileron servos are then Y to receiver channel 1

Top and Bottom Right Wing aileron servos are then Y to the receiver channel 2

For easier handling of the top wing servo connections , there are two more extension servo leads( left and right ) from the upper wing center support pylon through the fuselage to one arm of the Y for each channel .

Thus the upper wings have one more servo extension than the lower wings.

New Aileron configuration: Use 9 Ch receiver .

Eliminated Y connections, I now use one receiver channel for each aileron servo .

The overshoot / oscillation problem is with the bottom left aileron servo not the upper nor right wing servos .

I have replaced that "problem" servo already . The overshoot problem occurred until I finally replaced the 6 inch servo extension lead from the receiver to the left bottom aileron .

I have been "exercising " the servos at various times of the day, stirred the TX sticks and the "problem: servo seems solid to me . No more overshoots or oscillations . Sometimes there is a very small quiver at neutral position when the receiver is first turned on but it goes way after I move the ailerons . I am not sure what this very tiny quiver means . Do I still have a problem

I am using the 2100mah LIFE battery without regulators .

I was about the replace the receiver switch harness as well but decided not to because if it were a switch problem all servos would have been affected.
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Old 08-06-2014, 06:23 AM
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All servos are not the same, even the same model will have differences. Now you hook up Y harness and extensions and you have even more differences. Can a switch cause this problem, sure it can. Not likely but possible when troubleshooting don't rule out nothing. Until proven
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Old 08-06-2014, 07:00 AM
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The problem is interference. I just had this problem a few days ago. I ordered a new Graupner Y-harness and the problem went away. I even hooked up two older S3004 servos to the old harness and one of those servos had the same problem. I'm sure bad posts could also cause that, but for me, it happened when any servo was connected to the lead with the issue.

With the Graupner Y-harness in my plane, both servos are strong and have no issue with speed or power.
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Old 08-07-2014, 03:54 AM
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Originally Posted by Pete1burn View Post
The problem is interference. I just had this problem a few days ago. I ordered a new Graupner Y-harness and the problem went away. I even hooked up two older S3004 servos to the old harness and one of those servos had the same problem. I'm sure bad posts could also cause that, but for me, it happened when any servo was connected to the lead with the issue.

With the Graupner Y-harness in my plane, both servos are strong and have no issue with speed or power.
This is not interference, it is a bad connection in your old harness.
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Old 08-07-2014, 07:54 AM
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I agree that it's probably a bad servo connection. This is the first time I have come across this issue in all my 40 years in this hobby and I am having a horrid time nailing down the problem. I believe it's a combo of a marginal servo and poor performing servo extensions.
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