What is causing this servo problem?

[J-S-Q]

I have a problem with the DS510 cyclic servos on my TRex 500. On the bench, if I move the collective/cyclic controls for a while, one of the servos will occasionally lock up and stop responding to any stick inputs. If I give it a gentle tap it will immediately come back to life and start moving again. This can happen to any of the three servos at random.

Here's a short video showing the problem:

[ame=http://www.vimeo.com/14990043]Beast X Servo Problem (Align DS510) on Vimeo[/ame]

I've been using these servos for a while and they've never done this so at first I thought it was to do with the BeastX that I just installed. I removed it and plugged them straight into the Rx (Spektrum AR7000, powered by stock Align ESC). but this didn't fix the problem.

I have actually flown the heli about (8 flights) with this issue and everything was fine -I guess the pressure from the blades was constantly pushing on the servos and stopping them from 'going to sleep'.

Are there any servo experts here who could suggest what might make a servo behave like this? I doubt if all 3 of my servos have suddenly developed this fault overnight (I have had them a while and never seen them do this until now). My guess is some kind of power issue but it seams strange that I was able to fly the heli without any hint of a problem. It also seems strange that while one of the servos will lock up, the other two will continue to move.

I will probably try taking the rX out of another heli and see if that cures the issue.

Any thoughts?

[J-S-Q]

By the way, it still happens even if I disconnect the servo linkages going up to the swash so it is not to do with binding in the head. It even happens if I remove the servo, rx and ESC from the heli and test on the bench.

I suppose I should try powering the rX from a nicad battery and see what happens.

[Rotorhead]

Did you plug them into the RX individually?

If all three are doing it that suggests that either the RX is faulty, and the fault is temperature related (the time delay) or that one servo is drawing a lot of power and starving the other servos so they stop too, again this could be temperature (doesnt have to me much) related as a time delay indicates that it needs to heat up first before it happens, which could mean a bad solder joint somewhere is opening up.

I'd plug them in individually to try and narrow it down, and also try them with another RX if the problem persists after that.

[Ade_Law]

99% sure there is something wrong with the servo rather than it being the rx/tx

my suggestion would be to take the lid off the servo inspect the gears for damage. If theres nothing wrong there then its going to be a motor/pot problem which means replacing it or sending the servo off to be looked at.

Dont fly this servo until its fixed, its just not worth the risk.

Ade

[darrens]

How can it possibly be a servo fault if it can happen with any of the 3 servos at random, surely this has to be a faulty RX?.......OR..........JSQ doesn't mention whether he is using a BEC, but if so, this could be an issue if it can not supply enough power. many of the ESC's offer a BEC but have a range of cell counts available and if you go higher on voltage (higher cell count) naturally the amps supplied by the BEC reduce. Check the small print on the ESC manual if you are using a BEC.

[Ade_Law]

ooops how did i miss "This can happen to any of the three servos at random"

if you can get it to reliably do this on the bench try standard rx battery plugged straight into the rx. If it keeps doing it then you know its the rx if it doesnt then it has to be bec/esc related.

but still... dont fly it until you have tracked the problem down.

Ade

[J-S-Q]

I was also convinced it couldn't be a servo problem but now I'm not so sure. I have been using the stock Align ESC for power so far but I just tried plugging in the 2-in-1 regulator from my 700 and the problem was still there. I also tried a different receiver and the problem was still there.

So really that only seems to leave the possibility that ALL 3 servos are damaged. While I was setting up the BeastX, I did bind the servos a bit, but only very briefly and to damage all three is extremely unlucky. The annoying thing is that as I said above, I have flown these servos and they performed flawlessly and they must have been locking/unlocking occasionally (and instantaneously) during the flight.

Can anyone think of an explanation other than all 3 servos being knackered?

To Rotorhead... interesting theory about the overheating but I'm not convinced as there doesn't seem to be any pattern to the fault. i.e. it might not happen at all if you continuously move the collective/cyclic rapidly for 5+ minutes, but on the other hand, it might happen from the very first second when the servos are powered up from being completely cold.