Tail wagging

[wadders248]

I finally had time to maiden my Avantgarde this weekend. It's all very smooth and right from the first lift didn't require any cyclic input to hold it stationary.

The only problem is that no matter what I set the gyro to in my TX or parameter D in the Beastx I can't get rid of the tail wag.

I've also tried different settings for the governor in the Castles 80HV and pulling the tail to piece's to make sure it's as smooth as possible.

Mechanically the tail isn't the best I've experienced and there's a bit of movement in the tail pitch slider. The servo rod bends down a lot after the last boom guide, though I can't imagine either of these would be bad enough to continually wag.

The setup I'm using is:

FBL Unit: AR7200BX
Tail Servo: MKS669
ESC: Castle 80 HV
Tail Blades: Radix 95mm

I'm new to Castle ESCs, so I've attached the data log, just incase there's something that dosen't look quite right.

The only thing I haven't tried is to run the ESC without the governor, but any other suggestions are welcome!

[wadders248]

I'm not sure if this is the cure, though someone on Helifreak just mentioned this:

Sounds like a thrust bearing in the tail is backwards. Don't laugh, I went through 3 months of replacing and swapping and redoing things until I was told to and looked at tail assembly and one thrust bearing was reversed! Thrust bearing has two races and one with larger diameter goes closest to hub.

The manual doesn't mention that there's a difference, though new tail grips come with one race already installed. After I've taken them apart to check for grease and to make sure they were seated properly, I've mixed them about. So each side had the two of the same race on it.

The tail hub is also a bit stiffer to slide the bearings over on one side, so I might try another.

[Chris Boughton]

Check for endfloat in the tail output shaft as this can cause bad wagging problems!!! But like you said mechanical the tail has a few problems always try making the mechanical setup as close to perfect as you can before messing with the gyro gains and so forth, good luck

[Snaaakeey]

Re: Tail wagging

Tail gain gov gain or mechanical binding. Sorry I can't be much help as I'm not familiar with any of your gear. Gov off to eliminate that. Pop the servo ball link to the tail push rod and action it back and forth. It should be butter smooth ( compass tails always need the ball links reamed a lot. Any tightness or binding and you get a bounce). The only other things I would look at are length of tail servo arm(too long too much mechanical gain) or thrust bearing in the hub. My money is on tail binding either ball link or slider on the shaft or ball links to blade grips. They all have to be proper slippy!

[wadders248]

Check for endfloat in the tail output shaft as this can cause bad wagging problems!!! But like you said mechanical the tail has a few problems always try making the mechanical setup as close to perfect as you can before messing with the gyro gains and so forth, good luck

Good one, I'd not thought of that, though just checked and there's no float...

[wadders248]

Tail gain gov gain or mechanical binding. Sorry I can't be much help as I'm not familiar with any of your gear. Gov off to eliminate that. Pop the servo ball link to the tail push rod and action it back and forth. It should be butter smooth ( compass tails always need the ball links reamed a lot. Any tightness or binding and you get a bounce). The only other things I would look at are length of tail servo arm(too long too much mechanical gain) or thrust bearing in the hub. My money is on tail binding either ball link or slider on the shaft or ball links to blade grips. They all have to be proper slippy!

First thing I'll do tomorrow is turn off the governor, though now that I've got the thrust bearing races the correct way round, it feels smoother when you pull and twist.

You're right about buttery smoothness though... my mates Dune and Raptor tails slide almost even with a gently breeze when they're not connected!

[Chris Boughton]

Hmm well if all your mechanical setup is fine then its gonna be the electrical side, start of by double checking tht the servo pulse length and freq are set correctly. If they are all correct try decreasing Pot 3 on the bx tail dynamic as i noticed on mine it started to wagg when set too high, other that tht not much it could be really!! How are you on vibrations as bad vibs can cause unwanted wagging!!

[wadders248]

Hmm well if all your mechanical setup is fine then its gonna be the electrical side, start of by double checking tht the servo pulse length and freq are set correctly. If they are all correct try decreasing Pot 3 on the bx tail dynamic as i noticed on mine it started to wagg when set too high, other that tht not much it could be really!! How are you on vibrations as bad vibs can cause unwanted wagging!!

Yep, I was thinking about lowering pot 3 once I was happy that the mechanical movement of the tail couldn't be improved. The one part of the tail that doesn't seem right, is how the servo rod has to bend down to get the ball link onto the servo ball. I think I might put a step in the rod to lower it without it having to bend.

I've checked and double checked the pulse length and frequency and the heli is super smooth, there's not even transitional vibes as it spools-up.

[wadders248]

Success! I think the main cure was the thrust bearings being put back in the correct order, though all the other smoothing along the way must help.

I think there's still room for improvement, but it's holding nicely for now. I reckon you only need two rod guides and I think eventually I'll swap to using a 5mm carbon rod, adapted either from the Align 600 or Kasama Dune.

Thanks everyone for all your help!

[trillian]

I'm glad to hear you've solved the problem and it was nothing serious. I'm kinda surprised they didn't use a carbon pushrod for the tail in the first place.

[wadders248]

I'm kinda surprised they didn't use a carbon pushrod for the tail in the first place.

Me too... I think the tail servo rod is one of the few weaknesses of the whole heli. That and the position of where the rod connects to the pitch lever, which is too low and causes the rod to bend down after the last guide.

I know it's a more expensive kit, though the Kasama Dune has a control rod with a turnbuckle on the end, so you can adjust it without having to pop-off the rod. The Dune rod is the same cost as the Align 600 carbon control rod, but too long. I might get one and shorten it, then use the Align 600 tail boom guide, which is the correct size for the Avantgarde boom diameter!