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My trex 450xl just keeps wooping up and down, need help!

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My trex 450xl just keeps wooping up and down, need help!

Old 01-18-2007, 04:00 AM
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Default My trex 450xl just keeps wooping up and down, need help!

I have trex 450xl and JR x2720 and hi-tec 55 for cyclic and 65 for rudder, outrunner moter with JAS speed control and gy240 gyro. It flew effortlessly. My kid just crash it last 2 weeks. I just spend sometime to fix it last week. I replaced tail, washout, flybar and center hub to aluminium. The rudder servo case was cracked and pitch servo gear stripped. I've replace the case and gear and they function fine.

I started to set it up again and test flight it. It just keeps wooping up and down and also it tilting left and right all the time with nose down. I thougt it was o-ring in the center hub, but I can adjust the track with no problem. Then I checked the oneway bearing, it's as good as new. Then I checked the vertical movement of main shaft, there is no play there. Heck, I ran out of were to look.

Can someone point me out how to fix this? I'm getting frustrated now. Thanks
Old 01-18-2007, 11:33 AM
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Default RE: My trex 450xl just keeps wooping up and down, need help!

IS it CCMP? May have bent the linkage...check to see if the swash sit level at neutral pitch. does the swash move up and down and stay level?
Old 01-18-2007, 11:34 AM
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Default RE: My trex 450xl just keeps wooping up and down, need help!

IS it CCMP? May have bent the linkage...check to see if the swash sit level at neutral pitch. does the swash move up and down and stay level?
Old 01-19-2007, 01:38 AM
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Default RE: My trex 450xl just keeps wooping up and down, need help!

It's CCPM. I had a quick look at the linkages before and they seems pretty streight, but I'll have another look again over this weekend to be sure. The swash sits level and stay level. But I can say that it stay level when there is load when there is load. I'll have someone watch it when I hover it and hope it won't crash from wooping action.

Thanks, Roserx.
Old 01-19-2007, 05:43 AM
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Default RE: My trex 450xl just keeps wooping up and down, need help!

The gears in the HS55s are not that strong. You mentioned the pitch servo had stripped gears, have you checked the others?

A single tooth missing in one of the servos that connects to the side of the swash will produce free play in the link when the servo arm is in that possition, causing the side to side movement you're describing.
Old 01-21-2007, 11:16 PM
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Default RE: My trex 450xl just keeps wooping up and down, need help!

Thanks Karyn and Raserx. I just found out that the swash plate stay level at top and bottom of pitch, but not during increase or decrease the pitch. One of the servo seems to have free play. I will fix the servo first and then see how that goes. I'll post the update to what the outcome is. Thanks for all the help.
Old 01-23-2007, 11:42 PM
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Default RE: My trex 450xl just keeps wooping up and down, need help!

I think one of my servo went bad, i'll try to change the receiver with JR 9XII transmitter, just to check if that servo still act the same way. Then I'll move that servo from pitch (called by JR) to Elevator position and see if it still have the same behavier. Then I should know if I need a new servo. Just to make sure it the servo that cuase the problem!
Old 01-24-2007, 05:11 AM
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Default RE: My trex 450xl just keeps wooping up and down, need help!

Ok, changing the receiver don't change anything (still wooping). I switch the position of pitch servo and elevator servo, the fault servo(pitch servo now in elevator servo position) still acting the same way (some play in middle throw) but minimum pitch change at cyclic movement. Well, I'd better replace cyclic servos to new servos anyway. I have changed all gear in the servo, but it didn't fix the problem. So I think it from the motor itself.
Old 01-24-2007, 06:43 AM
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Default RE: My trex 450xl just keeps wooping up and down, need help!

While youre changing them, put in HS65s, the gears are much stronger than the 55s. You can use the metal gear vesions if you want, but the normal HS65 is plently strong enough for all but the hardest crash.
Old 01-29-2007, 01:28 AM
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Default RE: My trex 450xl just keeps wooping up and down, need help!

I got the 56 in becuase the lhs didn't carry 65hb. I have to cut out the body to make room for servo arms. they were way out of the body. The guy at the lhs should have told me about this. I had vibration (up and down motion) after I finished it. I have to replace the alu. center hub back to plastic one to get rid of the problem. I can't believe the alu is causin the problem. thanks you all for the help.

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