Hi all

Just wanted to share my weirdest heli problem I ever had. I have a T-Rex 600 NSP

Went flying last saturday, had a blast doing tic-tocs, multiple back flips and side flips and generally just going ape with my heli. At some point it felt asif the head speed was not what it should be and that the motor was bogging down a lot and the heli seemed to be more and more out of trim.

Anyway, landed, went home later and cleaned my heli, switched it on to check why it was so out of trim and the swash plate was all out of cente and skew, my blade pitch range in angle up was not the +12,0,-12 degrees but more in the region of +14,5,-8 or there abouts?

It was asif either the servo's have "forgotten" where the centre is or someone took the servo horns off, turned them a bit and put them back on the servo's!

Anyway, took the control horns off centrered the servo's put the horns back and heli was fine again, servo all working and had the correct amount of travel.

Under closer inspection, it looked like the servo horns actually slipped on the servo's!!!! I have HS-6975's on the cyclic, pretty powerfull servo's, so I guess that is possible.

Anyway, so from now on, I am checking the tightness of servo horns on the servo before each flight, that could have ended in disater.

Marcel

I have one question. Did you use hitec servo arms?

Was wondering if someone was going to ask that. Answer is no. Used them on another project that I had.

Went shopping for new ones when I built the heli, and my primary concern at the time was to get ones with holes spaced so that the link rods are parralell to each other. So I bought some standard white nylon ones. Looking at what happened, bad idea.

Not going to use those ones again so I will go shopping for some of those proper black thick unbreakable ones I got with the servo's.

I've had this happen even with Hitec servo arms, specifically the long black ones that come with the servos. It just happened on a 3D plank I have yesterday. the best fix is to go with the thick, red X type servo arms from Hitec. They never seem to slip.

Normally this will occur if you use Futaba arms on a Hitec servo. It'll work at first, but after the servo has been under a load for a while it will slip.

Every servo has a slightly different spline pattern. I have two drawers of servo horns for Futaba, Hitec, and JR. Even between these there are differnt sizes and spline patterns. Then I have another drawer that has bags containing servos for about 10 different horn splines with the servos they work on written on the bag. Not using the arm that came with the servo or one specifically made for that servo is stupid. Just plain stupid. I suppose you use the screws for plastic geared servos in the metal gear servos too....

Sorry but you almost lost your helo because of a dumb mistake.... I apologize for the rant....

So.. RappyPilot is dumb and Evan is a really smart guy. I'm glad we've established that. Now Evan can go back to work on quantum mechanics and the rest of us mortals can stick our fingers up our noses to the second knuckle.

There is no need to insult me evan-RCU. Looking at how long you have been a member at RCU leads me to believe you have probably made one or two more dumb mistakes than I have so far. That's how we learn.

I know JR horns don't fit Futaba for instance.

The servo arms I used was ones I got from my LHS after telling him what servo's I have. And the horns he gave me where not the ones that I got initially with the servo's.

According my LHS .... Futaba horns fits Hitec servo's, I trusted that to be true.

So yes, probably a dumb mistake that I made in hindsight, probably would never have become a problem if I was not doing anything else but hover around.

But, I have learned something new and still have a heli to fly ... An improved heli, now comes standard with uber strenth control Horns ... And they are screwed on with the right screws by the way

As I said sorry for the rant. The LHS was wrong in your case but there are some Hobbico, Tower, Hitec, and Futab servos that do happen to use the same horn. It is all very confusing and difficult, even for us smart people, again sorry.

Oh, to help... I have a set of calipers that I use to measure the inside diameter of the servo horns splines. Sometimes if you do not know if the horn is the correct one that may help especially since there are some that are visibly identical such as the white JR and Hitec ones.

No worries.

I think they should standardize them. One servo horn for al all servo horns for one ...

I fly planes as well and end up swapping servo's between them if needed. For some reason I tend to go through more planes than servo's I neatly cut off arms on horns that I don't need to prevent them from banging agains something and it looks neater. So I always run out of horns. The ones I had on my heli I also use in my planes and they work fine. They fit snugly, you can feel when you are using the wrong horn on a servo. They iether don't slide on or slide on to easily ...

But I suppose the forces that feed back to servos from a heli doing 3D is much much more than that of a 40 sized plane. At the end of the day I just used servo's that where not designed for such loads.

RappyPilot, I want to thank you for having the courage to share a mistake you made in an attempt to prevent someone else from making the same mistake. I thought that is what the forums were for. It's unfortunate there is always someone who makes you feel two inches tall.

It would be nice if they were all the same... or at least all the normal size seroc and then another size for the micros.

It was not really the controls pushing back on the servo but more the speed and torque of the servo pushing against the surface that moved the horn. We have servos that are so very high torque and super fast now.

One reason for the rant is so that Marcel realizes the significance.


He said;

Anyway, took the control horns off centrered the servo's put the horns back and heli was fine again, servo all working and had the correct amount of travel.

Under closer inspection, it looked like the servo horns actually slipped on the servo's!!!! I have HS-6975's on the cyclic, pretty powerfull servo's, so I guess that is possible.

Anyway, so from now on, I am checking the tightness of servo horns on the servo before each flight, that could have ended in disater.


The servo arm is the wrong one and needs to be swaped out with a correct one. Simply tightening up the screw will not fix the problem.

Let me clarify what I mean with "controls pushing back"

Imagine your heli up in the hair, doing tic-tocks. As you flip over and you change collective from full positive to full negative. There must be a significan load on the swashplate that "pushes" back and that the servo's need to counter to change a heli's collective. Therefore the servo's will do as told and as they are so powerfull, they will just turn regardless of the force on the horns stripping the horns, specially if using the worng ones.

And as far as checking the screws are concerned. If they are not tight, they could vibrate loose, or even fall out all together as the servo turns but not the horn thus slowly pushing the horn away from the servo therefore less surface area in the horn the servo to hold on thus slipping ... You don't have to be a rocket scientist to know if you are using the wrong horns all together that no matter how tight you screw them on they will slip.

Either way, I had substandard horns on my heli (For my style of flying) A good flying buddy of mine organised me some of those nice thick red ones that comes with the servo's. I reckon they will be ok with those.

So, I am done here. This thread is getting out of hand and is digressing from my original reason why I posted it.

I just wanted to share an experience with everyone. And as infernorcteam so nicely stated stated. Maybe someone else out there might read this and not make the same mistake and be as lucky as I was.

Happy flying all ....

Well said and again sorry that I came on so strong.