250 TREX250 PRO DFC big tail wag

[rappers]

Having built my first heli, an Align Trex250 Pro DFC, I have been trying it out in the field today. It flies really nice and is responsive to controls and is very stable in the hover, I think that I have a rather conservative setup at present regarding flip & roll rates. However, there is one thing I am having trouble with. The tail wags violently after doing a left or right turn. The wagging lasts for about two to three secs and then is ok.

The gyro gain is set quite low (55% in the Tx) just to keep the wagging down as I tried 60%,65%,70% but these settings just seemed to make things worse. Rudder gain shows as 32 in the software!

The rudder travel endpoints have been adjusted so there should be no binding. I didn't hear any after adjusting.

Does anybody have any idea of what I should try next? My rudder delay is set to 5. What is the best setting for this on a 250DFC?
I am using Align 3gx V4.0. The heli is completely stock build.

My flying day ended with a grub screw falling out of the tail rotor hub causing loss of tail function and subsequent tailspin and crash. I managed to get throttle hold on before it hit the ground, and suffered just a bent motor mount and tail boom!

Rappers

 

[Lee]

What radio are you using?
What tail servo is it?
If everything mechanical is set up correctly and smooth, then try this.

If its still wagging at 55% then just keep reducing it by 5% until it goes away.
Rudder delay shouldn't be needed, unless you have a slow cheap servo in the tail.
Any Digital tail servo shouldn't need delay.

 

[rappers]

Hi Lee, thx for your reply
I am using a Spektrum DX9 radio, the heli has the stock tail servo, DS425M. I am also using a sat receiver SPM9645.

I am confused about the gain setting on the radio as it's set to 55%. If I go any lower as you suggest won't I then be in rate mode?
I also noticed that the gain on the DX9 can be set -100 to +100.

Rappers

 

[murankar]

If I am not wrong, but 0 is your mid point for rate mode. I know on a Dx6i 55 would be an issue.

Sent from my LG-E980 using Forum Runner

 

[rappers]

Hmm, interesting, I didn't realise that 0 was the mid point for rate mode with my radio(DX9). So as Lee suggested my gain is therefore probably too high at 55%.
Thx, I'll lower the gain when I have fixed my crash damage.

 

[Lee]

Yep if your radio was 0% to 100% then below 50% would be rate.
But like mine, yours is -100% to 100% so as Matthias said, 0% is the mid point.

I have a gain of 23% on my heli, so I'd drop it down quite a bit from 55%.

 

[Tony]

Yup, anything above 0 in the DX9 is HH, and anything below 0 (negative numbers) is rate mode. On the DX8, DX9 and others like it, I suggest starting out with a 45% tail gain as a starting point. But yup, your tail gain is just a touch too high. You are close if the tail stops wagging, so lower it to 50 and try it, and if you see just a hint of tail wag after a hard stop, then lower it to 45 and you should be golden!

Sucks about the crash though. Make sure to use that blue thread locker on anything metal to metal so this doesn't happen again.

 

[Slobberdog]

the 250 is a pita with the tail, you don't say what gyro so guessing the 3GX

1. make sure you have zero binding in any of the links.
2. the two 681xx bearing mod is a good idea as it takes up a good bit of play in the grips.
3. the DS425m tail servo is relatively low torque and not quite fast enough for the 250 tail, lowering the tail gain will result in the tail feeling very loose. Best mod for the tail is the MKS Ds95i servo cures all wag issues straight away, however I found that the best mod I done was put a Vortex nano gyro and DS76T servo combination on mine, its great now

now there has been a lot of info and comments on this issue here http://www.helifreak.com/showthread.php?t=269597

 

[rappers]

Just come back from a great days flying at the field as summer finally showed its face in the UK today. I flew my repaired Trex250 with the gain now set to 30.
It flew very nicely, no longer any crazy tail wagging on turns. I had so much fun flying it I didn't get around to messing with the settings, so not sure if 30 is the optimum setting. I'll save that till next time. Thanks guys for all your help, couldn't have done that without you. Cheers!

 

[Tony]

If you don't have any drifting in teh tail, and no wag, then it's right in the sweet spot. Keep flying it and post up some video!!!

 

[NordCelt]

I had to do a lot of gain tuning on large industrial engine ECM's (electronic control modules). Generally a hunting back and fourth oscillation was too much gain and poor response time was too little gain. Will read more of the info above when I get a chance later because I just ordered a 250 Pro myself this morning.

 

[NordCelt]

Thanks for providing gain info. I'll be using the new Black DX7 so DX9 setting should work for me when I finally get that far down the road with my 250.

Congratulations on your success rappers.