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Old Oct 09, 2006, 02:51 AM
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Gloucester, England
Joined Aug 2006
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Gyro not working correctly after a crash

I think my Trex 450 CDE helicopter was set up just right, until a crash over the weekend. Before, the crash, when I gave the helicopter more throttle and it lifted off the ground the tail did not move at all in either direction; I am presuming that the gyro is, therefore, working correctly.

However, whilst flying around my garage I accidently clipped the wall damaging the tips of the wooden blades I was using. I have now scrapped the wodden blades and replaced with fibre blades. Although now when I give the helicopter more throttle I have to constantly apply rudder in order to prevent the tail from spinning around.

Also, when the helicopter is getting light on its skids (and training landing gear) it tends to lean to the right and drift to the right. What is causing this ?
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Old Oct 09, 2006, 03:10 AM
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Christchurch, New Zealand
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Which gyro?

Scrap those fiber blades; if you do the same thing with those again, you're going to need most of a new rotor head. Use wood blades until you can avoid crashing for a few months, then start thinking about carbon. The reason for the rotation is one of two things: either the gyro is in rate mode, and isn't trimmed right because of the higher torque required to spin the fiber blades, or else the crash messed up the mechanical trim somewhere, and you need to readjust it.

As for leaning right, that sounds like the normal result of balancing the tail rotor thrust... the tail rotor is going to push it to the left, you need a bit of right cyclic to compensate, hence the lean. Because you're in ground effect, the right side of the rotor disc being closer to the ground is going to make controlling that much more difficult, and it will slide to the right if you overdo the cyclic much more than it would a meter up. It is also possible that your training gear and/or heli is out of balance sideways, which is going to show up more with training gear than it would without.
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Old Oct 09, 2006, 03:55 AM
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Gloucester, England
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The gyro is an Align Head Hold.
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Old Oct 09, 2006, 04:04 AM
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Gloucester, England
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One other thing with the rudder. Sometimes I have the rudder lever on the transmitter as far as it will go and it will still not turn in that direction. I can't remember at the moment whether it is left or right. As soon as I put the lever back to centre it will then allow me to turn the rudder in that direction.

Also, with the two modes for the gyro on the transmitter. I am using a Futaba 6EXHP. What should the two percentage settings be with the level forward and backward.

I am not using carbon fibre blades, just the yellow fibre blades that come in the CDE kit. I will order some more wooden blades I think.
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Old Oct 09, 2006, 04:42 AM
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Christchurch, New Zealand
Joined Jun 2006
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Yep, those are the fiber blades to avoid.

I can't tell you your gain settings, they're too dependant on your precise setup, as in what sort of servo you have, how you assembled your servo mounts and tail pushrod, what sort of tail blades you have, what headspeed you're running, and how tight your tail belt is... get the picture?

It seems like you have the standard Telebee issues. They're not hard to fix, but it takes a bit of time.

So, to start with, always power up this gyro in rate mode (the opposite to what many gyros require).

Start the setup by zeroing all the yaw trims and subtrims for all flight modes. Now you're going to try to get the mechanical trim right by adjusting the position of the servo on the boom (or the length of the pushrod if that is convenient) till it will hover in rate mode with no trim or subtrim. You'll have to let the gyro warm up for a couple of minutes before you can get this right. If the tail wags, you've got too much gain; turn it down to stop that, you will probably be able to turn it back up later. A good place to start with is around 40%.

Once you have it hovering in rate mode and not wagging, you can then program the same gain in heading hold and try that. This time if it won't hold still after the gyro has warmed up, adjust the subtrim to sort it out. You'll have to land, switch to rate mode, and power off and on again several times, adjusting the trim each time, because every time you power up it resets the trim.

Now you should have it OK in heading hold mode, but it's probably off in rate mode. You can just ignore that if you want, but if you're really perfectionist, you can get it perfect in both modes by now going back to rate mode, noting how much stick it takes to hold it still, and adjusting the subtrim to HALVE that amount of stick, then going back to the beginning of the mechanical setup and doing it all over again.

After setting the centering up right (this might have taken as much as eight packs, by the way... I said it would take a while) you can then get the gain right. Be careful, if you can do this safely depends quite a bit on your flying skills. Basically, you want to flick the tail each way and observe if it wags, stops softly or stops dead. If it stops softly, turn it up. If it wags, turn it down. You're trying to get it to stop dead.

Obviously, if you're still on training gear, be very careful or you'll crash it... the best idea is just to turn it up till it wags a bit in the hover, then turn it down about 10% until you have enough control to be able to set it properly. You'll also have to remember to reset the gain when you take the training gear off, because the training gear gives the heli a whole lot more momentum in yaw.
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Old Oct 09, 2006, 05:04 AM
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Thanks for your help. Will try and have a look tonight.

How do you decide whether to fly with Head Holding or Rate Mode ?
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Old Oct 09, 2006, 03:14 PM
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I ran into this problem also after a mild tail strike in grass. I tried all the obvious things and after they didn't work I looked closely at the tail slider arm. It turned out that it had a crack right at the point where it attaches to the tail case and when the tail rotor was under load it would open up at the crack and not transmit the mechanical input from the tail link to the slider, however it worked just fine when the operated at zero throttle.

Something else to check anyway?

Mark
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Old Oct 09, 2006, 09:01 PM
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Palos Verdes, CA
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Quote:
Originally Posted by mmillerr
I ran into this problem also after a mild tail strike in grass. I tried all the obvious things and after they didn't work I looked closely at the tail slider arm. It turned out that it had a crack right at the point where it attaches to the tail case and when the tail rotor was under load it would open up at the crack and not transmit the mechanical input from the tail link to the slider, however it worked just fine when the operated at zero throttle.

Something else to check anyway?

Mark
Almost same thing with me too. Turned out servo case slightly cracked you couldn't tell until actuating, then the servo would move, not moving the rod.

Doubt there was gyro damage - likely culprit - servo, link binding, or like millerr says, the link arm....

And like all others have advised, ditch the yellow plastic blades. Not only do they not allow you to track correctly, if you do blade strike again, your blades will likely be intact, but you'll bust other stuff on the head. Better to shatter blades (woods) versus your head parts!
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Old Oct 10, 2006, 04:01 PM
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Just checked my tail servo and it moves approximately 90 degrees maximum in one direction, yet only about 10 degrees maximum in the other direction. Could the servo be broke ? I have checked the trim for channel 4 and it is zero.
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Old Oct 10, 2006, 04:14 PM
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United States, CO, Colorado Springs
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you need to center that servo. take the servo arm off and power up the sero so it will center it self. then put the servo arm back on 90 degrees to the case. then you will have equil travel in both directions. then adjust the servo on the tail boom so the pitch slider is centerd on the tail shaft. then adjust your end points so there is no binding in ether direction of travel from the pitch slider.........try that and you should be set.. make sure the rudder trim is set for zero first. you should not need any rudder trim at all. aleast i never have had to use any trim ever on my tail.
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Old Oct 11, 2006, 02:28 AM
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Gloucester, England
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I did take the servo arm off and try that. It is noticable that with the servo arm off, when I apply left or right rudder, the noise that the servo makes when moving in one direction is significantly shorter than when moving in the other direction.
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Old Oct 11, 2006, 03:00 AM
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Christchurch, New Zealand
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What's the subtrim on that channel set to? Something's not right...
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Old Oct 11, 2006, 03:29 AM
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I have a Futaba 6 EXHP so I don't think it has sub-trim. The normal trim is set to zero.
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Old Oct 11, 2006, 04:12 AM
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Ok, try the servo straight on the rudder channel without the gyro, and with the linkage off. If it still doesn't have equal travel, and the endpoints or travels and trims are all sensible, then there is something wrong with the servo; probably a stripped gear, and perhaps a bit of tooth is jamming it.
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