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t rex tail bobs up and down?

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t rex tail bobs up and down?

Old 12-27-2006, 07:48 PM
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Default t rex tail bobs up and down?

I have a trex SE and the tail bobs up and down about one inch when hovering,I have a 401 gyro with a 9650 digital servo...The heli will balance perfect on the mainshaft,I have the gain set to 50% on the gyro and there is no wag...The heliflys great besides this....any Ideas?
Old 12-27-2006, 08:58 PM
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Default RE: t rex tail bobs up and down?

The heli is balanced but are the paddles spaced accordingly on the flybar?
Old 12-27-2006, 09:25 PM
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Default RE: t rex tail bobs up and down?

I just measured the paddle spacing and it is perfect...the paddles do have a slight curve upward at the tips but that is the way they are drilled...I dont have any vibration, it is smooth as silk...the heli has only been flown for about a half hour and now the up and down movement comes and goes...do you think it may just need to "loosen up" a bit?
Old 12-27-2006, 09:56 PM
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Default RE: t rex tail bobs up and down?

If you are only a foot or two off the ground - it may just be ground effects causing the problem. Try going up to 4-5 feet.
Old 12-27-2006, 10:33 PM
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Default RE: t rex tail bobs up and down?

When I first cranked it up,it was almost impossible to fly ,but after doing some work to it like changing tail servo and loosening up tail belt a bit,it flew pretty well but will still do it ,but it seems to be getting better ,I am flying above ground effect at 5 to 10 ft. playing with the hover pitch and throttle seemed to help.when I increase head speed it gets worse.I think I will loosen up the gear mesh on the motor tommorrow a bit and see if that helps...good advice on the ground effect ...at first I thought it might be training gear picking up downdraft I took it off and still does it...
Old 12-27-2006, 10:55 PM
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Default RE: t rex tail bobs up and down?

Heres what I did so far and how it effected heli; 1. increased head speed...worse . 2 .loosened tail belt...better 3 .raise gain on gyro...started to wag 4 . adjusted delay on gyro...no difference... 5 .checked all tail linkage for binding... no difference... 6. adjusted pitch and throttle curves...still working on it...
Old 12-29-2006, 10:53 AM
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Default RE: t rex tail bobs up and down?

Check your ball links. I had the same problem and went over everything and couldn't find the problem. Then I decided to hold the skids down with my hand and run the heli up a little to see if I could find the problem. It turned out that it was one of the ball link screws - it had backed out of the swash for the elevator control, causing the heli to do exactly what you're describing. It was extremely easy to miss when checking over the heli.
Old 12-29-2006, 07:31 PM
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Default RE: t rex tail bobs up and down?

I will definitely have a look! Thanks....
Old 12-29-2006, 09:11 PM
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Default RE: t rex tail bobs up and down?

Ok Im getting closer to figuring it out...I noticed the ball links on one side were much tighter than on the other side of swash.Now that i have the heli trimmed in ,I notice that if you fly hands off or just fly with the rudder,it is smooth as silk ,but if you fly the cyclics it will bob for a second or two then straight out ...I am using hs 55 servos and a futaba 9c radio,set to full rates Ie:not dual rates...I think I can live with this now that I know its servo related...Does anyone use the new futaba S3154 digital micro servos on cyclic?I have UBEC 5v...Do they fit in frame without Mods what about flight times?
Old 12-30-2006, 01:39 PM
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Default RE: t rex tail bobs up and down?

It sounds like you are loosen just a bit of headspeed and this will cause a bob. Are you running Gov mode?
Old 12-31-2006, 03:24 AM
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Default RE: t rex tail bobs up and down?

I had it on gov mode but it was surging so much that I switched to throttle curves...Thanks for the info...I will check it out...could be something to it...
Old 01-01-2007, 12:08 PM
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Default RE: t rex tail bobs up and down?

I had a mysterious bob like that and finally tracked it down to a stripped servo, one tooth bad on the forward servo (elevator).
Old 01-01-2007, 12:38 PM
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Default RE: t rex tail bobs up and down?

What are you using for dampeners. The stock o-rings or a stiffer up grade? What about the shims the smaller or the larger? If you compress the o-rings too much it can cause bobbing like you are experiencing.
Old 01-04-2007, 06:34 PM
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Default RE: t rex tail bobs up and down?

Well im using the stock rotorhead which came prebuilt from align...Maybe its too tight?I will have to look into the the things mentioned...I will have to study a bit and learn how dampeners work...thanks...Dan

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