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Old 06-14-2012, 08:56 PM   #1
Jeff_Barrett
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Default My 7HV Tail Issues: Resolved??

Ok, so I've had this persistent wag since my initial maiden, and fighting it ever since. Mind you, this is the first time I've really had any time at all to work on my own stuff, in a long time .... so ....

At first, it was a real hard twitch every few seconds I had the gain down to 5% on my SK720 and it was still acting up ... hmm ...

I checked continuity from the tail case to the motor - that was good.
I checked tail assembly to make sure it wasn't binding - that was good.
I checked for any binding in the drive mechanism - that was good.

Bizarre. It seemed to happen after the governor took over on spool up, but then continued the hard twitch after landing with no throttle.

I swapped the SK720 with another that I had in stock and uploaded my settings from the original unit.

I took it to my back yard and spooled it up .... whaddya know?? No more hard twitch. Just a normal wag now. I had this unit on another machine that I hadn't flown (I built it and a friend wanted it so I sold it to him with out the SK720). I guess it was bad from the get go.

Well, again even with the new unit, I was down to 5% gain and it was still wagging. WTF right?!!

I checked the flight playback logs, voltage at the servo bus was nice and flat with no spikes, the vibrations were on average (almost a flat line) of less than 0.80 (holy crap that super low?!!! VERY impressive how smooth this bird runs!)

I was absolutely baffled, so I brought it inside and plunked it on the bench. I took the tail grips apart just to be sure I hadn't assembled the bearings wrong. Nope. Everything was together properly, so I put a little grease on the thrust bearings since they seemed a little on the dry side and put it all back together. That's as far as I got last night.

I also have a second rod guide holder on the tail boom. Ooops. It was loose, forgot the screws in it ... I'll adjust it tomorrow. It was riding about 6-8 inches from the frame, so I pushed it back about 14" from the frame thinking nothing of it.

Today, I got home and plugged the helicopter into the computer. I turned off the governor mode, saved, and head out to the back yard to test out a theory that the governor and esc were not playing nicely and causing the tail wag.

I plugged everything in and spooled up (man I love how smooth this helicopter spools) and lifted off the ground. No tail wag and at 50% gain! I bumped it up to 68% where I finally encountered a hint of oscillation, so I backed it down the 64% and tested it out - all worked great!

I spooled down and took it back inside where I plugged it back into the computer to enable the governor again. I wanted to be sure it was the governor and try to replicate the problem again so that I could give the feedback / data to Art @ Skookum to see if he might know the issue.

I enabled the SK-720 governor again and headed outside. I spooled up - everything good - governor mode kicked in - still good .... lift off .... tail holding. What the ...

Tail gain at 64% still and tail is holding solid despite flying in 30kph winds with gusts over 42kph ... not the best day for testing (or is it?? ) ...

I landed the beast and checked everything over in disbelief, then spooled up again and took off. Tail holding solid. Did a bunch of hard rudder movements in both directions and the tail stopped perfectly with no bounce or rebound.

I don't know what solved my tail issue, but I suspect it was one of two things, or a combination of both:

1. The second tail rod guide, I still haven't tightened it up, but it is still about 14" from the frame. I can't help but think this was the cause and binding.

2. Maybe something was sticking in the tail grip bearing assembly and taking it apart for inspection resolved it unknowingly.

Either way, I'm very happy now ... flight without a governor feels so touchy in comparison to flying with one. I figured I'd post this in case someone has a similar problem and might find some ideas to solve their own tail issues.

Here's my vibration log from my last hover ... I still can't get over how low it is!! You can see where I landed to look things over in disbelief and then spool up again.

For those wondering, I'm governed at 1950RPM.

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Old 06-14-2012, 09:53 PM   #2
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I really want to build one of these, but I have to be honest - the tail has me worried. I can't stand a tail that isn't rock solid. Seems like a weak point on an otherwise stellarly designed heli.
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Old 06-14-2012, 10:00 PM   #3
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Jeff,

Outstanding, glad you got it resolved, sir!


NRPY,

I have never had a tail problem on any Compass machine, including the 7HV. I helped diagnose one that had a tail wag, via remote control (phone conversation). The person was very sharp and had tried everything. I asked them to turn off the governor (this was not a Skookum governor, by the way) and the tail was fine with the governor shut down.

Same thing with a local friends Trex 500. He could not get rid of the wag. He shut off the governor (again, not a Skookum governor), and it was fine (so he has to tweak his governor setup).

Governor issues can cause tail wag in a variety of machines. I would always set the ship up without the governor first, make sure it is solid, then turn the governor on. If it wags only after arming the governor, the governor is not set up right, but you know the tail was correct (as it flew fine without the governor).

There is also a newer version of the 7HV tail coming out, to make it even better than it already is!
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Old 06-14-2012, 10:24 PM   #4
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Quote:
Originally Posted by NRPY View Post
I really want to build one of these, but I have to be honest - the tail has me worried. I can't stand a tail that isn't rock solid. Seems like a weak point on an otherwise stellarly designed heli.
NRPY ... most tail issues we've encountered either equate to a thrust bearing installed backwards, tail blades too small for lower headspeed, or some type of binding in the tail.

My issue was a little different as it was initially caused by a bad gyro (hard twitching). I highly suspect the second tail rod guide was the culprit here and causing intermittant binding, especially since it didn't have a screw to clamp it to the boom properly.

The winds were 30kph gusting well over 42kph this evening and the tail held ROCK SOLID. If that isn't a test, then I don't know what is.
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Old 06-14-2012, 10:25 PM   #5
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Congrats on solving your wag. I love reading tail wag success stories as they are so frustrating.

For what it's worth I had a wag on my 6hv that looked like a gain issue, twitchy. I was about to tear the tail apart, and low and behold, I pushed the tail grip link too far past the ball, which causes friction and misalignment (to your point > "some sort of binding"). Those are hard to catch on your own.

But again, congrats~
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Old 06-15-2012, 03:46 AM   #6
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It's great but it sucks when you fix something and aren't sure exactly why!

BTW that graph is super smooth, don't let the TDR guys see that
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Old 06-15-2012, 04:00 AM   #7
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Happy you got it sorted mate, this is my first 700 size heli and no problems with it, one of our clubs top flyers tested it for and he said what a lovely heli they are, made me very happy to be told this as its my first 700 size i cant say to much but i wil say im a very happy man
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Old 06-15-2012, 06:25 AM   #8
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Great stuff. Always bliss when you catch things like that on your machine!
The 7HV is sooo smooth and fast.

About the tail, I have never had any problem with it. Holds perfect, inspires confidence to do what ever, is really fast and accurate. All stock. BeastX3+curtis 105.
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Old 06-15-2012, 06:45 AM   #9
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To tuning the tail and solve some little wag problems i see this video.

He used compass bolt 06-0222 on the tail assebmly and not the pins.


Anyone else done this?
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Old 06-15-2012, 10:42 AM   #10
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Quote:
Originally Posted by Jeff_Barrett View Post
Ok, so I've had this persistent wag since my initial maiden, and fighting it ever since. Mind you, this is the first time I've really had any time at all to work on my own stuff, in a long time .... so ....

At first, it was a real hard twitch every few seconds I had the gain down to 5% on my SK720 and it was still acting up ... hmm ...

I checked continuity from the tail case to the motor - that was good.
I checked tail assembly to make sure it wasn't binding - that was good.
I checked for any binding in the drive mechanism - that was good.

Bizarre. It seemed to happen after the governor took over on spool up, but then continued the hard twitch after landing with no throttle.

I swapped the SK720 with another that I had in stock and uploaded my settings from the original unit.

I took it to my back yard and spooled it up .... whaddya know?? No more hard twitch. Just a normal wag now. I had this unit on another machine that I hadn't flown (I built it and a friend wanted it so I sold it to him with out the SK720). I guess it was bad from the get go.

Well, again even with the new unit, I was down to 5% gain and it was still wagging. WTF right?!!

I checked the flight playback logs, voltage at the servo bus was nice and flat with no spikes, the vibrations were on average (almost a flat line) of less than 0.80 (holy crap that super low?!!! VERY impressive how smooth this bird runs!)

I was absolutely baffled, so I brought it inside and plunked it on the bench. I took the tail grips apart just to be sure I hadn't assembled the bearings wrong. Nope. Everything was together properly, so I put a little grease on the thrust bearings since they seemed a little on the dry side and put it all back together. That's as far as I got last night.

I also have a second rod guide holder on the tail boom. Ooops. It was loose, forgot the screws in it ... I'll adjust it tomorrow. It was riding about 6-8 inches from the frame, so I pushed it back about 14" from the frame thinking nothing of it.

Today, I got home and plugged the helicopter into the computer. I turned off the governor mode, saved, and head out to the back yard to test out a theory that the governor and esc were not playing nicely and causing the tail wag.

I plugged everything in and spooled up (man I love how smooth this helicopter spools) and lifted off the ground. No tail wag and at 50% gain! I bumped it up to 68% where I finally encountered a hint of oscillation, so I backed it down the 64% and tested it out - all worked great!

I spooled down and took it back inside where I plugged it back into the computer to enable the governor again. I wanted to be sure it was the governor and try to replicate the problem again so that I could give the feedback / data to Art @ Skookum to see if he might know the issue.

I enabled the SK-720 governor again and headed outside. I spooled up - everything good - governor mode kicked in - still good .... lift off .... tail holding. What the ...

Tail gain at 64% still and tail is holding solid despite flying in 30kph winds with gusts over 42kph ... not the best day for testing (or is it?? ) ...

I landed the beast and checked everything over in disbelief, then spooled up again and took off. Tail holding solid. Did a bunch of hard rudder movements in both directions and the tail stopped perfectly with no bounce or rebound.

I don't know what solved my tail issue, but I suspect it was one of two things, or a combination of both:

1. The second tail rod guide, I still haven't tightened it up, but it is still about 14" from the frame. I can't help but think this was the cause and binding.

2. Maybe something was sticking in the tail grip bearing assembly and taking it apart for inspection resolved it unknowingly.

Either way, I'm very happy now ... flight without a governor feels so touchy in comparison to flying with one. I figured I'd post this in case someone has a similar problem and might find some ideas to solve their own tail issues.

Here's my vibration log from my last hover ... I still can't get over how low it is!! You can see where I landed to look things over in disbelief and then spool up again.

For those wondering, I'm governed at 1950RPM.

Great work Jeff, now time to start enjoying it

Quote:
Originally Posted by r.allington View Post
Happy you got it sorted mate, this is my first 700 size heli and no problems with it, one of our clubs top flyers tested it for and he said what a lovely heli they are, made me very happy to be told this as its my first 700 size i cant say to much but i wil say im a very happy man
Ron, [ It is Ron isn't it?] was that a certain person that owns every 90 sized machine going that said that?? Is good to hear when you've not flown any other big heli that its awesome.

Great stuff
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Old 06-15-2012, 12:44 PM   #11
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Quote:
Originally Posted by Mixmaster Pilot View Post
BTW that graph is super smooth, don't let the TDR guys see that
I have a TDR. I like it, but for all the elitist rhetoric about how well engineered it is, it doesn't look so hot when you put a vibration analyzer on it. The "inferior Chinese helicopters" I've tested are an order of magnitude smoother.
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Old 06-15-2012, 04:27 PM   #12
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I thought my Logo was smooth. The herringbone gear sounds so sweet.
When I took the FLYBAR off and put a Skookum 720 on it I found that it was about as smooth as a chainsaw. The tail was buzzing the boom with vibes in the high 20's and the gear/ motor interface was pretty bad
It took a lot of work and parts to get the vibes low enough to use the self level feature. I flew very well w/ the vibes but that can't be good
I can't wait to see what the vibes look like on my 7HV
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Old 06-15-2012, 05:43 PM   #13
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Quote:
Originally Posted by Jamesppp View Post
I thought my Logo was smooth. The herringbone gear sounds so sweet.
When I took the FLYBAR off and put a Skookum 720 on it I found that it was about as smooth as a chainsaw. The tail was buzzing the boom with vibes in the high 20's and the gear/ motor interface was pretty bad
It took a lot of work and parts to get the vibes low enough to use the self level feature. I flew very well w/ the vibes but that can't be good
I can't wait to see what the vibes look like on my 7HV
Funny you say that. The best I could ever get my 7HV was in the mid 100's without tail blades and mid 200's with a set of rails. With two different sets of kbdds it was in the 400's all which is still much under the "yellow" line in the v-bar. This was all done with balancing of the tail assembly.

My logo 600 was 50 without and <100 with tails on right out the box.
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Old 06-15-2012, 10:14 PM   #14
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Quote:
Originally Posted by Mixmaster Pilot View Post
It's great but it sucks when you fix something and aren't sure exactly why!


BTW that graph is super smooth, don't let the TDR guys see that
Yeah, it is a bother not knowing 100% what fixed it. But I have a pretty strong hunch it was one of the two things I noted. It HAS to be.

As a few guys already know around here, this build took about 6 months to arrive at this point ... not intentionally, it's just my time is limited with the business. That said, it did forced me to be much more methodical in my build.

By far, this is one of the best looking vibrations logs I've seen on one of my helicopters. I usually get between 1.5 and 3.5.



Quote:
Originally Posted by heathy View Post
Great work Jeff, now time to start enjoying it
Yeah, I was hoping to get to the field finally for the first time this year tomorrow, but it looks like mother nature wants me to stay inside and work on my buddy's 3D Plus to get him in the air. It's supposed to rain all day tomorrow.

What's your tail gain at on the SK720? I can't believe I'm at 64% with no wag ....

Quote:
Originally Posted by Jamesppp View Post
I can't wait to see what the vibes look like on my 7HV
Good luck! I can't wait to see your graphs too ....

Also, let me know where you end up on your tail gain.
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Old 06-16-2012, 03:24 PM   #15
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Jeff. I'm @ 46 in the TX gov gain @ 32
Rail tails. Outrage servo @ 8.4v

I did have to reduce my tail bank left stop accel to 28 to stop bounce back. Right side default 35.


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Old 06-16-2012, 08:38 PM   #16
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Quote:
Originally Posted by heathy View Post
Jeff. I'm @ 46 in the TX gov gain @ 32
Rail tails. Outrage servo @ 8.4v

I did have to reduce my tail bank left stop accel to 28 to stop bounce back. Right side default 35.
I didn't get a chance to test further today, I was helping out a friend with his 3D Plus (my old one to be precise).

I'm running the stock 115mm tail blades, MKS HBL980 @ 8.4V and the TX gain for the tail is @ 64. When testing the other day in the high winds, there was no tail bounce in either direction ... then again, the winds were awfully high.

I'll let you know how it turns out.

What are you governed at now?
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Old 06-17-2012, 03:27 AM   #17
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115's ? Have you retro fitted them? Thought 105's were in the kits. I decided not to use the stocks as they felt like something you would smooth out 2 PAC filler with.

Guess that's why your getting away with such a high gain!

I'm now settled on 1900 2000 2100 and seem to always be at 2100 due to the high winds here.


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Old 06-17-2012, 10:39 AM   #18
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LOL!

I'll go measure them again tonight, but I'm positive the yellow stock ones I received were 115s and look suspiciously like KBDD.

Right now, I'm governed 1950 across the board and it seems to be holding nicely in the high wind. I'll have to experiment a bit more.

Where did you settle on your cyclic gains?
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Old 06-17-2012, 11:13 AM   #19
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Mt #2 kit is newer than yours (March,12') and has 105mm Yellow Compass not KBDD's.

My #1 has same Yellow Compass 105's, bought October,11')
Maybe you got a bonus throw in from Mike or something.
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Old 06-17-2012, 04:25 PM   #20
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My yellow Compass stock tail blades measure a touch over 110mm
I bought this kit end of last month.
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