Violent random tail shake

[Aaron Hartwell]

Hey guys,

I have a T-Rex 500 ESP that I've been trying to get dialed in for almost a year now.

After trying virtually everything to get rid of a persistent and constant minor tail wag I finally replaced the Align GP 780 and DS520 with a new Futaba GY520 gyro and S9257 tail servo.

On hover and general forward flight my tail seems to be solid. When I punch out the tail seems to hold fairly well and piro's stop smoothly, no squishyness or bounce back.

However... When doing steep turns or big loops in fast forward flight I occassionally get a sudden violent tail wag that lasts for about four shakes and then it seems to settle down. When it happens you hear (WHOOP, WHOOP, WHOOP, WHOOP) as the tail is rocking back and forth. As a beginner it scares the heck out of me everytime it happens.

Any idea what this could be? As I said, hover and slow to medium forward flight seem perfect. You gotta get hauling for it to happen.

Thanks in advance,

Aaron

[whoanelly]

lower your gain some more,,mine did the same thing and i had to lower gain...

[DCP700]

We have been fighting that one also for a while on the 500 helicopters, You may have some wire shake from the airstream moving the gyro, or the tape that holds the gyro may be too soft for the heli/gyro/vibration level. I ended up using 3M trim tape as the Futaba tape was too soft. So far no more shakes as you describe. Before the tape switch, I couldn't lower the gain low enough to get rid of them.

[im4711]

Well gain might be one factor. However I would check the servo placement and wires. Make sure in such maneuvers that the gyro stays in place and wire is not moving violently and adding vibration to the gyro. In addition check if the wires from gyro to Servo and receiver are in good overall condition.

[Aaron Hartwell]

I can reduce the gain some. It is pretty high but I thought if it was too high I'd get a tail wag on hover?

Here's a picture of the gyro mounting. I suppose the black wire connecting the gryo to the little box that the servo plugs in could be moving. I thought I was supposed to leave it loose like that prevent vibrations getting transfered from the frame to the gyro.

[im4711]

Originally Posted by Aaron Hartwell

I can reduce the gain some. It is pretty high but I thought if it was too high I'd get a tail wag on hover?

Here's a picture of the gyro mounting. I suppose the black wire connecting the gryo to the little box that the servo plugs in could be moving. I thought I was supposed to leave it loose like that prevent vibrations getting transfered from the frame to the gyro.

Well that wire could be the cause of your issue. I would install it have the wire point backwards or sideways.In certain situation the wire moving fast in one direction could pull the gyro with it.

[im4711]

One more thing I noticed on the picture: You seem to use 2 layers of thick pads and the metal plate in between. Get one layer of thick pads without metal plate for this heli. Your gyro itself might be moving in some harder maneuvers.

[Aaron Hartwell]

Ok. So I should have one layer of foam on the gyro mount, not two with metal plate in between.

When do you use the two with metal? Larger or smaller helis? Or is it a gas vs. electric thing?

[flerpie]

Originally Posted by Aaron Hartwell

I can reduce the gain some. It is pretty high but I thought if it was too high I'd get a tail wag on hover?

Here's a picture of the gyro mounting. I suppose the black wire connecting the gryo to the little box that the servo plugs in could be moving. I thought I was supposed to leave it loose like that prevent vibrations getting transfered from the frame to the gyro.

I'd tie it down at the top loopy part with a dob of silicone. If that helps the problem
then maybe do something more permanent. I'd mess with the gyro plate and mounting
foams at a seperate time from the wire so I could tell which thing did it.

[Aaron Hartwell]

I reduced gain and removed the two foam pads and metal plate and replaced them with a single plate. I also secured the black wire going to the gyro loosely to the frame. One of the three things seemed to have fixed the problem.

Good idea on doing them one at a time to determine what the problem was. Next time I'll do that.

Aaron