Maintenance/melted rudder servo disk!

[Craneman]

Ok This heli is going to be working hard, shooting video and taking pictures at least four or five times a week. What parts wear the most or what should I keep an eye out for? I always inspect my helis after each job but this is a new machine for me so any suggestions are welcome.

Thanks

Juan Crane

[Craneman]

Well.... I learned my first lesson just now, I was hovering my EB at about 10 feet tuning motor, suddenly I lost tail control, the helicopter started spinning like crazy I managed to stay calm hit throttle cut and autoed safely. I proceeded to inspect the heli and found the rudder servo disc had broken and the pushrod had sliped out of the disk. I grabbed the pushrod and touched the screw and bolt (which were still attached to the rod) and too my surprise they were burning hot!!
upon carefully inspecting the servo disk I noticed it had not actually broken it had melted!

The only thing I can think of is vibration heated the screw and bots so muche they melted the servo disk.

I never thought this could happen how do you guys concet your pushrod to the tail servo?

See pics

[Craneman]

Well I got an answer on RR that explains it, here's the explanation:


"Seen it before on RC aircraft - it's vibration telegraphing

Seen two different cases : one actually started a fire !

1st time was on a 60 size old school 60 piped pattern bird
" Banshee" in which we had a contact line fit between the lower plywood saddle located bulkhead F2, and the contacting surface of the heavey glassed center section of the wing .

Landed the bird, could smell something burning like wood. Remmoved the wing and the complete saddle and plywood was charred black and smoldering. Once we gave it a bit of air it really took off ! Needless to say we poured a can of pop on it.

2nd time was on a set of the earley style plastic grey type pinned hinges on a vertical fin in a Byron F-16. We could see scale like smudges traveling horizontally from the pin across the rudder.

We thought it was a nice scale effect till we noticed that the metal pin in the knuckel of the hinge had actually melted thru 6 of hinge's!

I would try to kill the resonance of the carbon rod "de tune" by soaping up a couple sections of silicon fuel tube and slide them over the rod.
Won't take much to kill the harmonic's"

[cbergen]

Holy Crap!!

I've seen a humming tail pushrod before but never anything like that!!

Did you SEE the pushrod resonating? Was there any noise, like a hum, that you might get with a vibe?

We do recommend teh use of a velcro strap, a wrap around the boom, then continuing around the pushrod. This velcro does 3 things.

1. dampens out any resonances from having the long rod unsupported for such a length.

2. Supports the pushrod, preventing it from hanging down.

3. When the velcro is tucked up under the front of the horizontal fin, it also acts as a buffer between the pushrod and the boom support.

I'm looking for the pic I've posted of this setup, but have not found it yet.....:(

[bcook01]

Perhaps the ball link was too tight causing friction induced heat. I cannot see where a harmonic would generate this form of heat..... fatigue yes.

BC

[cbergen]

Just had a thought, what headspeed were you running?

[rkeith2]

Like this?

[Craneman]

I 'm not sure about the head speed, but I am running the motor at about 75% for the first three tanks and I think I was a little on the rich side.

No visible vibes or sound, but I wasn`t really looking.

I already installed the the velcro, that should do it, ball links are ok now, I used polishing compound and my dremel on the balls, fit is perfect now and I blinged out my balls
Smile

[PaulH]

I used polishing compound and my dremel on the balls ... I blinged out my balls

:rolling