I keep stripping servo gears on HXT900 servos

[gloobnib]

Title pretty much says it all. I've gone through about 20 of these now and am getting tired of constantly having to replace them. About 1/2 of the time it is my fault due to crashing, particularly on the FT-22 (full size) and fT-Delta. Basically if I wind up crashing (ground, tree, coming in too hot on a belly landing) at least one of the servos is toast.

But I've definitely had them strip mid-flight on my fT22 and on my bix3. On the bix 3 It was the flaps servo that stripped so I was able to save it by switching off flaps quickly. On the FT-22, it just spiraled in after it was stripped. I can accept that crashing damages planes and that is part of the hobby. But if I can spend less time repairing, I can spend more time flying. Many times the only damage to the plane is the stripped aervo; otherwise it is ready to just pop back up in the air.

So really 2 questions:
1) Is it possible I just got a bad batch of these? I ordered them all (24) at the same time. But I've also read that these are basically crap and you can expect stripped gears as part of the bargain price.
2) if I upgrade to some beefier metal gear servos, can I realistically expect to spend less time repairing, or am I just going to move the failure point to something else like a servo arm, control horn or (worst case) control surface?

Thanks in advance for guidance!

ETA: It occurs to me that the FT22 elevons and the bix3 flaps are both very high loads, so maybe I'm expecting too much out of cheap servos. On the bix3 I love going stupid slow/short on landings with full flaps set at about 60deg deflection. And I'm not shy about whipping the FT22 around when doing aerobatics.

 

[KRAR]

You probably just pushing the servo to their limit and past...

I would recomend a more decent servo, not necessarily a Metal gear setup...

the Hitec HS-55 is still full nylon. They are $10 a servo though.

You can also check out:
https://twistedhobbys.com/micro-servos-5-11g/

They make foam 3d planes that are meant to be thrown around....I have their servos with their planes and the servos last longer than the planes after about 3-4 crashes...

I also know Horizon hobby has a 9 gram servo but it is $15 or so...

I seem to remember using the hitec servos on the smaller RC helicopters... so they are sturdy..

 

[ViperTech]

Yep, you hit the nail on the head the FT22 has huge control surfaces and I popped more than 1 servo on that FT22. When the C/S is huge go with metal gear when you can. Yep you got the old flea bay chinesium knock offs that I bought and they were all basically crap except I bought the 12 pack.

 

[Ran D. St. Clair]

After 40 years of flying I have never stripped a servo in flight, and only a few in crashes (my fault). Servos overloaded by flight loads should back drive, or not hold position, but the gears should not strip. You definitely have some crummy servos. You may also be using them inappropriately. Spend a little money and buy better stuff. Historically speaking, servos are incredibly cheap now days, and the speed, torque, durability, and small size have improved dramatically. Better servos have replacement gear trains available, though at $5 to $10 for something reasonable, most people don't bother.

 

[Bricks]

Along with the cheaper servos of which I use a lot of it could be your setup not helping the situation. Using the farthest hole from the servo puts more stress on the gearing and offers less servo torque. Try using one of the closer holes on the servo arm and using a farther hole on the control horn. Before I set up any control surface I go in my transmitter and set my servo throws as far as they will go with out stalling the servo doing this first will give more resolution of the servo.

 

[Montiey]

Hextronik has some metal gear 9grams. You may want to check them out. A stronger nylon servo, however, would still cost less and weigh less.

 

[gloobnib]

Thanks all for the input. And yes, it sounds like this is a "you get what you pay for" situation.

I'm now starting to realize that I may need to re-examine the frugal ways from my youth. I came to FT to learn to build my own planes because I'm cheap. But there is a time/money trade-off that made sense when I was young, broke, but with copious free time. Now I'm old(er), comfortable, and free time is at a premium. So maybe spending 3x-6x for quality servos now makes sense. I also sort of came to the realization that saving $12 on servos is putting about $75 in other electronics at risk should the $3 servo fail.

As for repairing servos - I think I'll draw the line there. I saw you can buy replacement gears for the HTX900s on HK, but why pay $.99 for gears that will be used to repair a $3 servo? Plus my eyes aren't what they used to be, so the thought of trying to disassemble/repair something that small makes me cringe even thinking about it!

Anyway, thanks for the feedback. One thing I didn't really think completely through is the torque/leverage on the control horns and servo arms. It makes no sense to use only 30% of the total available throw at high leverage on a servo. Better to use 100% of the throw at 1/3 the required torque. I'll also look into extending the servo throws through the tx as well.

 

[SoylentGreen4579]

been using hobbyking metal gear servos almost exclusively. I have lost only one in the past two seasons ... internal meltdown, gears were perfect

 

[TazRC]

I've had really good luck with Emax servos, both metal and plastic gear.

 

[TooJung2Die]

I'm using metal gear servos more because I'm tired of plastic gear servos locking up while flying. Usually you can get them unstuck by banging the sticks but if you're too close to the ground when it happens it's all over. The extra 3 or 4 grams for a metal gear doesn't make much difference. Mount them closer to CG if possible.

 

[Bricks]

Another problem may be your hinge on your control surfaces being to stiff loading your servos even more. I use nothing but the cheapest servos I can find and have very seldom stripped one out except in a crash. I have used a ton of these and have been happy with the

https://www.aliexpress.com/item/50p...2432470707.html?spm=a2g0s.8937460.0.0.kLdN5Cm.

 

[gloobnib]

Hextronik has some metal gear 9grams. You may want to check them out. A stronger nylon servo, however, would still cost less and weigh less.

So I ordered a few different types of servos to replace the HXT900 servos that I was having trouble with. I started with some more powerful nylon geared servos but almost immediately ran into an issue that I think is overloading of the BEC in mini-sized ESCs.

Basically while in flight under high Gs, the receiver would reboot. I initially thought maybe it was my radio glitching as the sequence of events was: "Telemetry lost", plane starts to flop down for 2-3 seconds, "telemetry recovered", and then I have control again. But if it was actually the radio glitching, the plane should have gone into failsafe, which would have included activation of the gyro's self-level feature. Later testing on the bench confirmed that if I banged the sticks to an extreme position and then put some leverage on the control surfaces, the radio would reboot. I can't find any specs on max current draw on a 9g servo should be, but the BEC is only rated for 1A at 5V.

I then moved to a metal gear Turnigy servo that, so far, seems to be working for me. I may try swapping in a beefier ESC with the beefier nylon geared servos to see if the problem with radio reboots goes away.

This whole flight electronics stuff is a lot more complicated than I thought!