What can be done about TOO MUCH collective and cyclic pitch?

[spackermen]

As posted in the Compass Helis forum...

Ok, so here's what I'm working with

Atom 500
Converted to FBL from FB kit
Align DS 510 Servos
Mini Vbar
Compass FUT horns, set to inner position for ball spacing
Inner swash, tried spaced out and non spaced ball positions
Using "lower" head mounting hole, (makes head spacing taller)

And here's what I have in Vbar programming

Zero collective setup at mid stick,
Radio ATV all calibrated as shown in videos, etc. for +100/-100
Then I go into the collective setup page and run into my first problem. I get unholy amounts of pitch from this setup. I have the slider to 59 (as low as it can go) and have stil around 15' of pitch. Then go to the cyclic page, same story, at 60, the cyclic range is still at 9' (was at 10 with FBL arms on spaced out inner swash balls)

Anyone have any insight into what is causing this? I was told by several people that to use the compass horns, and the inner position for ball spacing, and it would be good. However, it's not turning out too well so far. Haha. I did watch the videos, and spent quite a long time searching around for answers, however I cannot even come up with any good numbers for servo horn ball spacing. Is it too far out? I can see, as others describe in other threads that with the servo horn at 90' the link does not run paralell to the main shaft, however doesn't seem to be an issue with other atoms running the same setup.

I did find this

http://rc.runryder.com/helicopter/t621360p1/

however it looks like he fixed it with a new swash. Atom just has one compass swash correct or no?

Is it ok to turn down the endpoints of the servo travels? I have tried drilling new holes in the servo horns at 15mm, and still have inordinate amounts of pitch.

This is what I have been doing :

This is what I want to be doing



Any and all positive input is greatly appreciated.

More information can be found on

http://helifreak.com/showthread.php?t=285031

[wangotaco]

I had a similar problem on my trex 600. The advice I got was to shorten my arms on the servos. I already had them in as far as they would go, so I ordered new ones and moved them in further. I am currently at 21mm, but, that certainly doesn't translate to the distance you may need. At 21 I am able to get within the envelope (89 I think) on the collective. It's weird, I am still at 75 on the cyclic at 8degrees. If I come in any further on the length I start getting challenged with the center of the servo getting in the way. If I go outside instead of inside the angles get weird. Anyway, long story short, shorten the distance between your servo center and the ball.

[spackermen]

The wierd thing is that others have the EXACT same setup and are running fine. Even without drilling new holes and moving the ball in on the servo horn. I was checking it over tonight and if I check cyclic on the "front" blade, I have 10 degrees one way, 5 the other. If I check on the "back" blade, (over the tail) I have 8 degrees, and 15 degrees. What would cause that?

[RoyArms]

Sounds like you dont have servo arms 90 at center sticks, zero degrees pitch set at center sticks via the link length adjustments, and level swash in all collective positions.

[spackermen]

Checked with a dial indicator today. All positions are level within .003 in. Went through and created a new setup today, and still not working out. I don't know where to go from here. Especially where there are others that have the same setup and don't have problems.

[Andy from Sandy]

With push-pull indirect servo to swash there is a couple of problems. By moving the balls in on the servo end you will now have the links non-parallel and this is a binding situation. If the length of the output arm on the bell-crank at the swash is longer than the input you get a gain. The distances need to be equal. Once that is done if your collective is still way to much then you need to move the ball out on the blade grip.

[spackermen]

The atom uses direct to swash mixing. When I moved in the balls the links were even worse for parallel to the main shaft than they are normally. I see your point though all geometry needs to be square to prevent binding and can even cause some funky interactions.

[TheBum]

Other than servo arm distance, the only thing I can think that would help collective pitch is changing the spacing on the grip arms. If you can somehow space them further out from the grips, the angular change in the grips will be less for a given amount of swash movement. It will also affect cyclic. I saw somebody with a Compass head do something like this.

[keepnitflying]

http://www.vstabi.info/en/geometry

Last section.

.

[spackermen]

Interesting I've not seen this before. I've read that page a hundred times and just realized. My grips have a centerline to driver center of 21mm. The mikado has a distance of 31. That cant be helping. Granted thats for a larger Heli than I am working on.

[X-Gear]

if your servos are centered, everything at 90 degrees to each other, swash links built so that the swash is at 1/2 travel, center stick and blade grips mechanically adjusted to zero, plus tx calibrated correctly using subtrim and endpoint adjustments to -100, 0 and +100 in the tx calibration screen, then you will have nearly equal pitch on pos and neg. You have something not centered, adjusted or built right for such a large pitch difference.

Every conversion that i have done on 50 and 90 size machines, the magic ball spacing number seems to be 21 mm (quick uk makes some aluminum wheels that have 21mm spacing if you want aluminum). It doesn't matter if the links are not parallel (think of a 4 link setup in a drag car). There is no binding.



You only need to change the ball spacing at the servos, not both ends.