Servos Servo failure?

flysolo

flysolo

Member
I think it's been like this for the last 10 flights. Would you still use it?


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It's the tail servo of an Align 550dfc. Seems good at high speed but not at low and always sounds like it's binding.
 
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I would not read too much into that Turnigy servo tester. I can assure you, the signal coming from that is not as clean as it is coming from the Rx. Plug it into the Rx in the rudder port and test again and post back. I will bed that sound goes away. That 655 is a bitchin servo, I use the same one on my 600N and it's SOLID! Let me know.
 
I agree, plug it into an Rx and see how it behaves. I usually grab the servo horn or the link to give it some back and forward pressure while moving the servo through range of control to see if it is binding up or any teeth are missing on a gear. If that's the tail servo, unless you planted it hard -- torque tube tied into a pretzel hard -- chances are it is fine. I've stripped gears on cyclic servos, but never a tail servo (including plastic gear ones) despite some pretty aggressive hits. They just don't see much back force on them, including in most crashes.
 
Don't bash my tester, it's great. I use it ALL the time :)

When plugged in to the rx it's not really noticable because it moves the servo fast and I've been flying with it like this for some time and to me it seems pretty precise.

I only noticed it because when moving it by hand it feels very different from when it was new. Almost like it's stuck(but not in one special place) and when you move it you get momentum and it moves to much, it's not possible to move it just a little bit.

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If i just connect it to the Rx it still sounds like it's binding but it seems to move ok. ONly when moved really slow is it starting to jitter.
 
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If the feel has changed moving it by hand then you might have a gear stripped or warped. Could happen if your push rod is at an angle which is creating a mechanical stress on the servo and warping gears as it tries to work.

If you are worried about the noise, this digital servo is a high speed servo and under no load it will make wierd noises as and even oscillate a bit if you put a longer arm on it .. As its trying to find the true position and oscillating and the finest touch will make it calm down. In flight all servos are under load so they don't cause issues .

If you are worried about the gear, and notchiness, open it, inspect it, grease it and put it back together. Even sometimes an angles mount (not 90) will cause the case to warp and Gears not align properly. Unlikely on such a big servo, and unlikely till you are just smacking the crap out of this bird. But it can happen.

So check that for peace of your own mind :)
 
Yup, I was also going to say to check your gears just to make sure. And when you put it on the Rx, set your gain to 0 (no rate, no HH) and move it that way. YOu should be able to move it very slowly that way. But I would be checking the gears if it were mine.
 
Thanks, I can definitely feel the difference when moving it by hand but it doesn't feel like the gears are stripped, not sure what warped means :) Think I'm going to put a new one on there for now and check the inside later.
 
warped means when you spin the gears, one of the gears goes up and down. Basically meaning the gear is not "true". Hope this makes sense. It would take a pretty hard hit to warp the gears in a full size servo though.

I think the issue with this servo is exactly what gaba said above. This thing is so fast and so precise, that it has to jump to keep up with the signals that the servo tester is sending out. The servo tester may be telling it to go from degree1 to degree2 and the servo is expecting a response to go from degree1 to degree1.1, then 1.2, 1.3 and so on. The servo wants those very precise signals, and I'm thinking that tester is more broad in it's signal. Hope this makes sense.
 
Ok, thanks for explaining. Could be warped maybe.. I'm doing a complete rebuild of the heli, moving all the telemetry stuff and re-wiring to get everything perfect so I'm not gonna risk it I think. The tester has worked well on other servos, I always use it to center them, but it could be that this servo is too fast/demanding (needs better resolution? don't know if that sounds right in english, it's what i would say in swedish)
 
Resolution! That is the word I was looking for! I know the 655 is one of the newest servos on the market, so it has the newest motor, pots and so on in it. Either way, no matter what you decide to do, let us know how it goes.
 
Yeah, worth opening it up, wiping down the gears and seeing if there are any metal filings in the gear meshes. Doesn't sound to me like something it stripped. It would be grinding really bad, getting stuck and stalling, etc. at least that's what happened when I stripped a gear in a DS615 cyclic servo.
 
pvolcko said:
Yeah, worth opening it up, wiping down the gears and seeing if there are any metal filings in the gear meshes. Doesn't sound to me like something it stripped. It would be grinding really bad, getting stuck and stalling, etc. at least that's what happened when I stripped a gear in a DS615 cyclic servo.
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I stripped the gears on the 450 (ds415) many times and it is like you are saying, they grind or get stuck and so on. So I can tell by feeling this servo that the gears are not stripped, at least not the same way as the others. I got a replacement for it now, gonna make another video to show the difference between the 2
 
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