Can too much gain fry a cyclic servo?

[Nihilistic]

I've recently been tweaking my 450 FBL build's cyclic gains, per Dr. M's tweak guide. I've been flying it for a while with the cyclic gains set to 55 on the main screen, and it flies well, but I wanted to see if I could get maximum hold for the typical windy conditions we've had here lately. I increased the gains to 60, and flew out a pack in 10 MPH winds, and it seemed to hold beautifully, with no sign of disc oscillations. Bumped them up to 65, and it still seemed fine.

I just now jacked the gains up to 80 while on the bench, and moved the helicopter by hand noting how much more quickly the swash reacts to tilting the helicopter. I intended to reduce it back to 70 and try flying another pack, when one of my TGY-211DMH cyclic servos (Channel 1) stopped responding! I got that tell tale twitch of one of the other servos that happens when one of the three are dead. Tried resetting the ZYX-S and checking the servo lead, to no avail.

I had to replace the (Channel 2) servo a while back because it started failing intermittently after a bad crash. I got a few flights out of it after rebuilding, but then it started to stop responding, and became untrustworthy. The crash was bad enough that it broke the servo arm, and sheared off one of the bolts in my Tarot Split Lock DFC head.

I've had dozens of good flights since then, with no incidents, mostly FFF, with a little bit of soft 3D, like loops, flips, and rolls. Definitely no smack 3D.

Can jacking up the gain too high on the bench fry a servo? None of my test flights showed the disc wobble one should expect when you've reached maximum cyclic gain. Or, are these just shitty servos?

They sure seem to perform well when they're working. They center well, and seem to be plenty quick enough, and I suppose have enough torque. The specs are similar to the Hitec 5065MG's that are popular for 450 helicopters. The cases have really nice sturdy mounting tabs, with aluminum heat sink centers. They make the servo push rods line up nice and straight with the swash when mounted from the outside of the frame, which makes installing them a breeze (no need to remove all those frame screws to mount them from the inside). They seem like really good-bang-for-your-buck servos at about $18. I know a lot of other ZYX users like the TGY-306 for their greater torque and faster speeds, though. Are the TGY-211DMH's just not up to the task?

EXI 450 SE V2 clone frame with belt driven tail
EXI Volcano 40A ESC with 3A 5V linear BEC (barely gets warm after a 7 minute flight) Turnigy H2218 3550KV motor with an 11 tooth pinion
Spektrum AR6200 receiver with satellite
Turnigy TGY-211DMH cyclic servos
Hitec 5084MG tail servo
Tarot Split Lock DFC main rotor head
EXI carbon fiber 325mm main rotor blades
Turnigy 3S 2200mAh 20C lipos
Spektrum DX6i TX setup according to the Tarot FBL manual with 40% pitch and roll expo, none for the tail.
ZYX-S firmware 4.02
Settings are the stock Soft 3D preset with a few tweaks listed below
Cyclic Agility's both increased +5 to 40
Cyclic Gains +25 to 65 (last successful flight though for most flights they were at 55)
Advanced Menu:
Cyclic D Gains decreased -15 to 15

[Dr. M]

I don't think it's the gain. The servo probably failed because of internal issues.

But I am a bit surprised you could go that high on the gain and not see oscillations. You're probably running really low head speed. And short servo arms.

[Nihilistic]

I'm running the Turnigy H2218 motor with an 11T pinion. My ESC timing is set on medium. It's a 3550kv rated motor. I might be better off with the 13T pinion. I get 7 minute flights easy out of it as it is.

The arms that come with the TGY-211DMH only have three holes. I originally put the balls in the middle holes, which is close to the recommended servo axis to ball distance. But, my collective pitch setting was -56 to get +/- 12 degrees pitch. According to your guide you recommend to move the ball in a hole to stay within the 60 to 80 range. I moved them in, and my collective pitch setting is now -70. But, the distance is only like 9.5 mm or something I think. We discussed this in another thread a while ago. You said that's how you have yours set up.

I guess I just got some bad servos. I hate that servos seem to be such a hit and miss proposition in this hobby. I haven't had that many flights on this build for servos to be wearing out. The gears weren't stripped at all. And there was no obvious sign of anything burned up when I took them apart to look. I was hoping maybe a servo lead had come unsoldered or something easy to fix. I guess the motors on them burned out, or a chip in them. I'm going to try to get HobbyKing to send me a new one without having to go through the hassle of returning them. If not, I might just buy one more, and if another goes bad, RMA 3 of them. And give up on them and try another type of servo if those go bad.

As annoying that it is to have two of these servos go tits up on me...I've been lucky both times it happened on the bench, and not in the air causing a crash.

[Nihilistic]

According to this online head speed calculator, http://www.readyheli.com/headspeed-calculator.html


I should be getting just over 3,000 RPM with my 11T pinion at the start of a fresh pack. Is that too low? I'd get about 3,600 if I put the 13T pinion on.