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Jul 08, 2017, 02:27 PM
Robert Gennings

Top Flite AT6 retract problem

This is my first plane with mechanical retracts. Didn't think it was that difficult but hard lesson learned......burned up two retract servos. The retracts came with the plane and they operate correctly and with no binding when I push or pull on them by hand, so theres no binding/friction problem. After the servo installation and connecting the servo arm to the two operating rods, the gear operates fine though the servo seems to 'twist' on its mounting screws when the gear is operated and for a regular servo that would indicate the need for a travel adjustment. But we know that a retract servo is not adjustable. The servo works fine for a few cycles but once I turn everything off and restart say the next day, the servo fails to operate. Its burned out I guess. I replaced the first servo, thinking it was defective, but the same thing happened with the second one. Unless someone can point me to a fix, I think I will replace this gear with air retracts; don't want to risk a third servo burn out. What am I doing wrong?
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Jul 09, 2017, 06:13 AM
No bounce, No play.
davidmc36's Avatar
Can you move the control rod to a hole closer to center on the servo arm? That would allow the servo to travel farther without binding up.

Pics or video might help.
Jul 09, 2017, 03:36 PM
Robert Gennings
david mc36: Thanks for your suggestion. Yes I have a replacement servo coming, so I could move the rods closer to centre as you suggest. This would reduce the travel but then would the gear lock into place at each end of its movement? Seems to me that with mechanical retracts the 'stroke' of the control rod has to be quite precise. Too much travel = binding and servo burn-out; too little and the gear won't lock. Maybe this is why folks give up and convert to pneumatics..........
Jul 09, 2017, 05:31 PM
No bounce, No play.
davidmc36's Avatar
Originally Posted by joangennings
... Maybe this is why folks give up and convert to pneumatics..........
That's pretty much it.

Delicate balance. Maybe a wee bit of rod length change to balance between how much the closer hole changes things.

I am thinking about custom linkage or jack-screw for a long term creation.
Aug 12, 2017, 07:59 AM
Registered User
Cougar429's Avatar
You pointed out the one biggest flaw in the T/F design, and one of the biggest pains to fix.

The first is their stock gear wire. The geometry has the gear facing 15 degrees forward and any flex tends to act down and aft, launching the plane back up in the air. That wire, and the replacement from Robart, flexed too easily and stays there, preventing the wheels from fitting back into the wells. Suspect that may be the factor that burns out the retract servo.

Tore out that setup and went with servoless retracts and heavily modded struts, (shortened for this app) and landings were much more controllable. Still had problems in that the front gear mount hangs unsupported on the inboard end. Ripped that out and made complete mount assemblies that bonded to the spars.

Sent a PM with a link to my build thread.

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