TREX450 Sport 3GX violent shaking on liftoff

[steeleagle]

TREX 450 Sport converted to FBL with Align FBL head and 3GX upgraded to V2.0 (my first FBL conversion). Setup all parameters pretty much as per the defaults and all seems to be operating the way it is supposed to. Elevator and Aileron gain set to 60%. Rudder gain at 68%. Swash is level and pitch is 0 at 50% stick. Spoolup is smooth with no noticeable vibration. I have throttle curve set to 45/70/75/80. Pitch curve Normal 40/INH/50/75/100. Heli starts to liftoff smoothly with no roll or pitch tendency but then starts to shake violently as soon as it lifts off. Seems to me it must be mechanical and not the 3GX . Any ideas?

[mukenukem]

Did you use the inner holes on the servo arms ? This is needed for the changed geometry.

Also it is helpful if you have more than one throttle curve, so you can change rpm if you get a resonance.

Try reducing gain on the shaking axis.
All blades (main and tail) balanced ?

[badfrog]

Everything Mukenukem said above... also, check to be sure your pitch is identical on both blades from 0 on up.

[steeleagle]

Thanks, I will check the rods are on the inner servo holes and set it up again. The blades were balanced with "0" pitch both sides and tracking was checked. I was also going to tear the head down and double check everything there as well.

[mtuccio]

Sounds to me like your gains are still too high. Try turning down the pots on the 3GX and see what happens....

[bad007]

Originally Posted by steeleagle

I was also going to tear the head down and double check everything there as well.

That's a good idea. make sure the thrust bearings are installed correctly and the inner half is pushed in the whole way. Sometimes they need a little extra push to get them to settle the whole way in the grip.

[JRAY]

Make sure your TT gears are OK. I just ran into a similar issue with a friend's used 450 and some of the TT gears were slightly stripped, found it quickly by dumb luck really. Also, make sure that if you are using sats, that you have the gyro sensitivity on aux2 and not the gear channel in your tx, otherwise, you'll be adjusting the governor gain and not the gyro. Ask me' how I know that......

[steeleagle]

Reset everything up, using inner servo holes, rebalanced blades, new mainshaft, levelled swash, redid the whole 3GX setup using a gain of 50 on the pots. Hovers as smooth as silk. Thanks for all the input!

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