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Help with Trex 450 flight control problem


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Ozzief16a
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Location: Pensacola, FL area

PostPosted: Sun Nov 03, 2013 5:53 am
PostPost subject: Help with Trex 450 flight control problem
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Hello all,

I am the proud but frustrated owner of an Align T-Rex 450. I am also new to the sport of
rc heli flying, approximately 5 months. As Newbies are prone to do, I had a very hard tail first
landing that resulted in me replacing the tail boom and support struts, landing skids, etc. I have not
been able to fly my 450 since the crash due to a tail rotor control actuation problem.

I will try to explain my problem: When I increase the throttle to near 50% and the heli gets light on
it's skids the heli will start to yaw (piro) in one direction or the other (which is normal)Let's say
to the left. When I move the rudder stick slightly to the right to oppose the yaw the heli goes into
a rapid right piro. Then when I make a rudder input to the left to oppose the right piro that I induced
the heli goes into a piro to the left. These piros are so rapid that the heli is unflyable.

I brought the heli inside to investigate the problem. I found that the tail rotor was moving in the correct
commanded direction when rudder inputs were made, but it then "froze" in that position instead of returning
to the neutral position commanded by the heading lock system when I moved the rudder stick back to the rudder
centered position. I found that, using the rudder stick, I could move the tail rotors from their centered
positions progressively out to their end points and they would stay in their last commanded position instead
of returning to center after I centered the rudder stick. By the way the tail rotor control linkages all moved
smoothly through out their full range of travel. There is no binding or resistance at all.

I suspected that the problem might be in the Heading Lock mode of the gyro or perhaps the gyro itself. I unplugged
the motor power wires then powered up the heli. I rotated the heli's nose left and right by hand to varify that the
Heading Lock was working, heading lock pitched the tail rotor blades in the correct direction in response to
me yawing the heli left and right. I also installed a new rudder servo to eliminate it as a possible source
for the problem. I borrowed and installed a friends spare gyro to see if my original gyro was the culprit. The
test results were the same with the newly installed gyro, the heading lock feature worked correctly by moving the
tail rotor blades to counter the left and right yaw that I induced by rotating the heli's nose with my hand.

This is a real head scratcher for me, I'd appreciate any help that my fellow heli drivers can give me on this.

Regards,

Larry Osborne
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Burgess
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PostPosted: Sun Nov 03, 2013 9:30 am
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Hello Larry,


If the tail pitch slider isn't binding, then a little more technical info would be good.

The version of the Align 450 that you have.

Make and model of the Gyro.

Make and model of the transmitter.

Transmitter settings relevant to the gyro and rudder channels.



Burgess
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tombo242
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Location: Santo Estêvão, East Algarve, Portugal. Now 82, but still feels 22.

PostPosted: Sun Nov 03, 2013 6:16 pm
PostPost subject: Re: Help with Trex 450 flight control problem
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Hi Larry,

First off I agree with Burgess - we need more information.

However, taking this part of your post:
Ozzief16a wrote:
I will try to explain my problem: When I increase the throttle to near 50% and the heli gets light on
it's skids the heli will start to yaw (piro) in one direction or the other (which is normal)Let's say
to the left. When I move the rudder stick slightly to the right to oppose the yaw the heli goes into
a rapid right piro. Then when I make a rudder input to the left to oppose the right piro that I induced
the heli goes into a piro to the left. These piros are so rapid that the heli is unflyable.

This is the exact description of a gyro working in reverse - but you say that the blades move in the correct direction when you pivot the heli. These two things are totally incompatible. Is there any chance that you could be mistaken? Can you try reversing the gyro and let us know what happens? You do not seem to have tried this. A video of the tail when rotating the heli by hand would be useful to us.

Tom.
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admiral
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Location: Brisbane, Australia

PostPosted: Sun Nov 03, 2013 7:36 pm
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Hi Larry,

Been there done that a couple of times, Thombo is right tail servo and Gyro working against each other, can be caused by

1. tail drive belt reversed,
2. Tail Blade grips reversed.

On a fly barred model as easy as reversing the Gyro, but better to find out what is setup wrong.
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Burgess
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PostPosted: Wed Nov 06, 2013 12:05 am
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Keith, I think you got it...DoR of tail rotor, providing it's synchromesh belt drive rather than a shaft drive.

When refitting the boom, the synchromesh drive belt needs to be given a quatre turn when engaging onto the drive pinion, easy mistake to turn the wrong way.

All the linkages would still work in the correct sense, but the tail rotor would turn in the wrong direction, consequently the response to gyro would be in the wrong direction too.

Tail rotor blades turn anti-clockwise, coming up into the down wash from the main rotor.

Burgess
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tombo242
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PostPosted: Wed Nov 06, 2013 1:15 am
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Good thoughts from Keith and Burgess there Larry, but I would still like to see a vid of the problem as words like "moves in the correct direction" may not always be true. We have all had problems like this in the past and unless they can be seen are impossible to solve (or nearly so).

A picture is worth a thousand words - but a video is worth a whole bookful.

Tom.
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Ozzief16a
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Location: Pensacola, FL area

PostPosted: Sat Nov 09, 2013 7:57 am
PostPost subject: Help with Trex 450 flight control problem
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Tombo, Admiral, it turns out that you are both right. I reversed the gyro on
the heli and the uncontrollable piros ceased. I am a happy heli flyer again,
thank you all.

Larry
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Burgess
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PostPosted: Sat Nov 09, 2013 9:32 am
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Larry,

Where the self exciting rotation piros have ceased by reversing the gyro sense. Which direction is the tail rotor now turning, clockwise, or anti clockwise?
If clockwise, than their turning trailing-edge first.

Burgess
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Ozzief16a
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PostPosted: Sat Nov 09, 2013 10:30 am
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The tail rotor blades rotate counter clockwise as seen from the starboard side of the heli.
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tombo242
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PostPosted: Sat Nov 09, 2013 11:50 pm
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Good on yuh Larry mate, glad it's all done and no sweat.

Tom.
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