Head Wobbles on Hard Collective Stops

[mahbouni]

Originally Posted by Mentalic

Head looks normal as far as I can tell from the one pic of the swash. A view from above the swash would help.

Photo attached. I pinched the pitch link with the back of the swash plate to make sure it's phased with the elevator servo linkage. To me it looks like the blade grips are out of phase with the swash plate. There isn't anything I can adjust as the swash driver arms are fixed to the head itself. I know from my Logo 600 that the head can turn slightly on the main shaft during the first few flights and a 2nd adjustment of the swash driver was always necessary to correct the phasing, When I built my 700 I didn't preload the head on the main shaft before tightening up the bolts. It is possible that it has slipped a bit. I did tighten it up as much as I could without damaging the thread in the head block.

[mahbouni]

OK, I have loosened the head bolts but it doesn't make any difference. Even if the head does slip on the main shaft it does not affect the phasing because the swash driver arms are attached to the head. So my head block is out of phase with the swash plate. I'm now pretty convinced that this is the cause of the problem but I have no idea why it is like that. I'm trying to see if I built the head incorrectly in any way

[mahbouni]

I removed the radius arm links from their ball joints and aligned the head with the swash plate by hand. You can see in the attached photo that the radius arm over reaches the ball joint. It's as if it's too big, or perhaps the swash driver arms should be further out. I used the 3x5x0.5mm washer shown on page 13 of the manual. Either way my heli definitely has a mechanical phasing error. There's definitely something not right with the head geometry.

[Mentalic]

Originally Posted by mahbouni

The plate is glued in. Already tried putting load on the servos, and swapped the aileron servos around to see if it rolls to the other side. These servos have less than 50 flights and worked perfectly in a Logo 600SE before I transferred them over.

You can't tell if it's square from looking at the previous photo. This is how I checked it

Think I'd use something other than a ink pen. Suggest checking with a strait edge referenced to the frame, not the boom.

Sensor off square will act like a phasing problem. You could resort to adjusting phasing in vbar but I know, who wants to do that? You definitely have a good problem going here.

[mahbouni]

Yes I've done all that. The pen was just the nearest thing I could get hold of today to show you. In any case it's more accurate than looking at a photo. When I mounted it I did actually use a ruler against the frame. Anyway, I've seen much worse mounted sensors flying much better than this. This is really bad. On a good heli I'd have to mount the sensor so badly that it would be obvious from any angle you look at it.

Look I'm not new to this and have set up so many Vbars for other people that flew well. I had a bunch of guys look at this yesterday and they didn't think the sensor was mounted badly. These guys are pros and are among the best in the UK.

The problem is with the head. The head is out of phase with the swash driver. It's plain clear now that I'm looking in the right place. There's no way this heli would ever fly straight no matter who sets it up. When the pitch link is in phase with the elevator servo, the blade grips are out of phase by a lot. That is totally wrong! I'm not talking about the delta offset at the blade grips. It's at the swash plate. The swash driver arms and radius arms give incorrect geometry.

I'd like someone else to post a picture of theirs to show me its just mine that's wrong, because if they're all like that then there's a big problem with the Logo 700 period.

[rcmarty]

The pic with the swash driver offset .. Is the other one connected up causing this much of an offset ?

I'm starting to think the head might be machined wrong ? If the ears aren't right where the drivers mount it will mess up the phasing.

Anyone have a head that flies straight to test ?

Martin

[mahbouni]

Originally Posted by rcmarty

The pic with the swash driver offset .. Is the other one connected up causing this much of an offset ?

I'm starting to think the head might be machined wrong ? If the ears aren't right where the drivers mount it will mess up the phasing.

Anyone have a head that flies straight to test ?

Martin

No they are both disconnected. I rotated the swash plate into phase by hand so I could see if the radius arms line up with the ball joints, but they don't.

I was thinking maybe the ears are machined too far in. There's a flat surface recessed in and perhaps its too far in. I'd like to try adding a shim to see if it fixes the problem, but yes comparing it to another 700 would be a good idea.

[mahbouni]

I'm quite happy to bring this heli to the Zone competition next month and let the Mikado team check it out for themselves.

[rcmarty]

I took some pics of my 700 for you.

Head set to center if throw by eye.


If i had to split hairs and say the links to the grips aren't 100% vertical , but after a closer look , it looks like a washer/shim is needed under the ball to grip connection. Spacing it out to get the ball more in center with the center of head.

Martin

[mahbouni]

Originally Posted by rcmarty

If i had to split hairs and say the links to the grips aren't 100% vertical , but after a closer look , it looks like a washer/shim is needed under the ball to grip connection. Spacing it out to get the ball more in center with the center of head

Thanks for the pics. That is normal. There is an intentional delta offset at the blade grips so the linkage rods, so they won't be vertical. It's by design.

My problem is with the bottom linkage. I can't get the head block in phase with the swash plate unless I disconnect the radius arms.

Any chance you could measure the width of your head block at the ears, where the swash driver arms bolt to each side, please? I measured 22mm

[mahbouni]

Today I shimmed the Swash Driver Arms by 2mm on each side with 0.5mm washers. This allowed me to get the head block square with the swash plate. I took it for a test fly this afternoon and BINGO! Flips are straight. There is no more rolling to the side in either forward or backward flips. There are still some small wobbles at the endpoints of hard tic tocs but that's down to Vbar setup and I can tune them out. I probably should have cleared out the Optimizer settings before testing. Anyway, I now have a heli that flies straight, so I am most happy.

I would still like to know if this issue is just with my Logo 700 or is it on all of them. I measured the width of my head block where the Swash Driver Arms bolt onto it and it was 22mm. With 2mm shims on either side it is 26mm. I wonder if on the Logo 800 its also 26mm but only 22mm on all the Logo 700's.

[Mentalic]

Originally Posted by mahbouni

Any chance you could measure the width of your head block at the ears, where the swash driver arms bolt to each side, please? I measured 22mm

Mine is 22mm as well. When the swash driver links are disconnected they land perfectly on the balls.

[mahbouni]

Originally Posted by Mentalic

Mine is 22mm as well. When the swash driver links are disconnected they land perfectly on the balls.

Interesting. I just now checked to see if mine were machined at an angle but they are straight. If I put the edge of a ruler against the ears it runs parallel to the blade grips. So I can't think what's different on mine to yours. All I know is that it had a phasing error before and now it doesn't. The photos I posted don't show it as bad is it was because of the camera angle but when actually looking at it the head block was clearly advanced several degrees from the swash plate. It flew crooked before and now it doesn't. Using washers is not an elegant solution so if I need to replace a part then I would like to find out what it is. If I've built the heli wrong then I'd also like to know what it is. But on Sunday I had my heli side by side with Rob Barnes' one from Midland Helicopters and we couldn't tell any difference. Although we didn't check the phasing of the head at that time.

One thing I'll say for sure is that if 22mm is the correct width then the Logo 800 better have that too because they can't both have correct geometry if they're different.

[mahbouni]

Today I went to see another Logo 700 and compare it with mine. It has the same phasing error in the head. When the linkage is in line with the elevator servo linkage, the head is not square if with the frame, although it looks slightly better than mine was. I flew it and it has the same behavior, although slightly better than mine was. When doing a half flip forward it ends up leaning to the right. when doing a half flip back it ends up leaning to the left. In elevator tic tocs it wobbles from side to side.

[stocksy27]

checked mine head block measures 22m, when i pop the swash driver arms off they still line up perfectly with with balls on the swash

[mahbouni]

Originally Posted by stocksy27

checked mine head block measures 22m, when i pop the swash driver arms off they still line up perfectly with with balls on the swash

I would leave them on and check if the head is square with the frame when the pitch linkage is in line with the elevator servo linkage. It actually takes a good eye to spot it and get the pitch linkage dead center with the back of the swash plate.

[Feeback]

I'll be darned, it's off by a fair bit indeed.

[rcmarty]

I read your post over and over , i think i have it figured out what your saying.

I lined up the swash ball center with the center threaded section of the anti rotation bracket.

Then stood over top the heli and the head aprear to be rotated (clockwise) past 90 degrees a little bit.
Guestimating 1-2 degrees.

I was doing elevator tic tocs to day (heavy on the pitch ones as i'm still working in them) and it did seem to do a wiggle when going back and forth. You need to be watching for it. Once you do a complete one it ends up in the same place in the end except for the wiggle in and out.

Am i on the right track ? Or do i have this thread in the back of my mind and i'm seeing things ?

------------

You shimmed out the driver arms , rotating the swash counterclockwise. Then when you re align the elevator pin to the swash ball it would bring the head grips square to the frames.

Of course this would make the delta (i recall) angle of the swash to grip link to increase. Did you shim the ball to the grip out a bit also ? Or does it fly ok with an increased delta setting ?

I'm going to go check the 800 now....


Martin

[rcmarty]

Me again..

I did the same test on the logo 800. ( hopfully still OT )

The logo 800 is more out.

On the other side the swash to grip link is far more vertical. I suspect there directly related.


Do you have a pic of your swash to grip link after shimming the driver arms ? Is the angle more ?


I wonder if this is an issue with the design or (more likely) that the headblock is machined a bit much.

( i don't know if these parts are made in house or farmed out )


Still love my logo's. Got 6 flights on the 700 now with the last 2 going all out. This thing will take all i can do and laugh at me on the way by.

Simple fix is a bonus.

Martin

[mahbouni]

Originally Posted by rcmarty

I read your post over and over , i think i have it figured out what your saying.

I lined up the swash ball center with the center threaded section of the anti rotation bracket.

Then stood over top the heli and the head aprear to be rotated (clockwise) past 90 degrees a little bit.
Guestimating 1-2 degrees.

I was doing elevator tic tocs to day (heavy on the pitch ones as i'm still working in them) and it did seem to do a wiggle when going back and forth. You need to be watching for it. Once you do a complete one it ends up in the same place in the end except for the wiggle in and out.

Am i on the right track ? Or do i have this thread in the back of my mind and i'm seeing things ?

------------

You shimmed out the driver arms , rotating the swash counterclockwise. Then when you re align the elevator pin to the swash ball it would bring the head grips square to the frames.

Of course this would make the delta (i recall) angle of the swash to grip link to increase. Did you shim the ball to the grip out a bit also ? Or does it fly ok with an increased delta setting ?

I'm going to go check the 800 now....


Martin

You are absolutely correct. Your photos show exactly what I got, perhaps slightly less severe.

The delta offset at the blade grip arms is irrelevant to phasing as the rotating axis of the blade grip does not change phase with the swash plate. The linkage rod does not have to be absolutely vertical but the ball link at the bottom needs to be centered with the head block.

In flight, yes you do need to be watching for it. I didn't notice mine until a friend pointed out the wobble while I was doing simple elevator tic tocs. In smooth flight I never noticed it because I was subconsciously making corrections. The hang time on this heli is unreal and you can practically do things in slow motion. But in hard fast maneuvers where I don't have time to correct it showed up.

To me its important though. I bought my Logo 700 because I wanted the most accurate flying heli I could buy