"Warning": T-Rex 700 flybarless elevator servo overheating

**GravityKills** · 04-05-2010, 07:45 AM

OK, this is not a warning in a sense that a product is faulty. More like a mistake that's easily made and can get quite expensive.

In a flybarless-converted 700, the servos need to work much harder than in the standard flybar version. As a result, they tend to get hot.
In the 700, the elevator servo sits in a plastic enclosure, preventing airflow. It gets even hotter, stops working and / or fails.

This happened to me in Corfu with a 610 DS (failed) and a JR 8717 (temporarily lost torque), both at 6.3 V.

In that sense, the upgrade below might be a good idea if the servos are hot to the touch after flying. I ordered one today, but haven't tried it yet.

Fast Lad Performance

So what happened?
My 700 worked fine for several gallons in Finland on 20 % nitro. But apparently, the Corfu heat, 30 % Optifuel and me flying a little bit harder than usual (still like grandma... when she hasn't taken her pills

) were too much for the DS 610, which failed, probably with a broken poti.

Since the LiPo was discharged more deeply than usual, it seems that once the servos get too hot, they lose efficiency, draw even more current, get even hotter...

PS this happened with a Mikado V-Bar. People say that it makes the servos work harder than the Align system, don't know if this is true.

**moonmanflyer** · 04-05-2010, 11:43 AM

Yep that was the save of the week when your 700 went all wibbly wobbly Marcus, might you, it was flown to death over the week, must be in need of a major service.

**darryl** · 04-05-2010, 12:40 PM

i have one those fitted to my 700... purely cause i'm a tart. lol

Seriously though I noticed the smallest amount of flex in the plastic housing so decided to change, no problems to report.

**busterboy** · 04-05-2010, 04:27 PM

Nice tip Marcus.

Got them fitted in my 700's already for two reason.

1: airflow

2: bling

**barney** · 04-05-2010, 07:38 PM

I'm running 3 x 610's on my stretched Trex 600 3G. 4-5 times now I've had the elevator lose its positioning during flight resulting in a semi controlled elevator see-sawing motion of the helicopter. The elevator gyro appears to loose its neutral positioning. Mostly its been a fairly mild but on two occasions it's been a handfull.

If you manage to sit it down you can lift off again as the Elevator gyro regains its proper neutral positioning.

I've also had it tuck up violently at very high speed as I started to gently pull up into a huge loop. Reckon the servo ran out of power/torque. The used were fitted at the same time as the 3G so only had a few weeks use.

At the moment its been removed as its already cost me a set of blades and my confidence in the system is tarnished. I know its not a cable/plug issue as I popped the cases to make sure the pins in the cables are fully located which they are..

Its a shame as it really straightens out a heli and I like the positive feel of the controls.

Did your model display these symptoms at any point?

thanks Brian

**GravityKills** · 04-05-2010, 07:52 PM

This sounds exactly like an overheated elevator servo.
The symptoms were a bit different, but that depends on the flying, of course. The heli got slow to respond, started to wobble and drift.

>> If you manage to sit it down you can lift off again
... as the elevator servo cools down.

>> Reckon the servo ran out of power/torque
... as it heated up

try to fly it for a minute, then feel the temperature of the servos. In my 700, it was very obvious.
Shorter servo horns might help, although on my 700 they were only 9 mm, which is already quite short.

The JR 8915 which I used later recovered fully, once it cooled down. They do lose torque when they get hot, that's a fact: I had a broken blade grip bearing in my 550 once, making the blade grips lock up. The 8915 on swash overheated to the point when the heli didn't respond at all to stick movement. Apparently they survived the ordeal, several hundreds of flights later they are still going strong.