Geometry Problem on Vibe 50, Ideas ?

[huckzilla]

Okay here is my set up:

Vibe 50, 140 deg swash 1:1 setting
Cyclic servos JR 8311, balls @ 13.7mm ( as close in as they go on JR HD servo wheels )
FBL Head - RJX
Everything 90 degrees, swash plate leveled with Trueblood leveler.

I can set 6 degrees cyclic in step J Blue LED goes on just before 6 degrees is reached, about 5.5 degrees. Then in step K, I adjusted collective to +/- 10 degrees ( have run 12 with this set up before no problem )

Step L Swash Plate Limit:

Aileron limit, a lot of throw about 15 degrees. Elevator limit I get only about 10 degrees. The blue LED for aileron and elevator limit come on just before binding so that is okay; blue LED w/o binding.

Step L Issue - One of my aileron servos moves to its extreme limit and stalls, totally dead no power. Only after releasing some throw does it turn back on. If I drop the aileron or elevator cyclic swash plate limit a click or two it wont over drive and kill the servo but I cant get the blue LED's in step L. The other solution I have found if to drop my collective pitch to 8 degrees +/- which is kind of lame.

I think that I need to get less cyclic travel with more servo wheel movement to fix the problem. Issue is the manual says how important big cyclic throws are.

I would appreciate suggestions, anyone else run into this ? Anyone with a Vibe 50 140 swash @ 1:1, whats your geometry ??

Thanks guys hopefully I can get it figured out for this weekend !!!

Dan M.

[DannyvG]

Originally Posted by huckzilla

Step L Issue - One of my aileron servos moves to its extreme limit and stalls, totally dead no power. Only after releasing some throw does it turn back on. If I drop the aileron or elevator cyclic swash plate limit a click or two it wont over drive and kill the servo but I cant get the blue LED's in step L. The other solution I have found if to drop my collective pitch to 8 degrees +/- which is kind of lame.

I had the same problem with my BLS451 on my Trex700N when using a very small servohorn. The servos seemed to move out of range or something and could just be moved by hand without any force.
I just limited the cyclic throw a bit.
Later I replaced the servo horns so they had a bit bigger arm length. And then I got blue at 5.9degrees or something.
You could go out on the servo horn and change some of the ball links on your swash or blade grip to change the leverage ratio.

[huckzilla]

I was considering going further out on the horn despite the decreased resolution. I really don't like driving the servos that hard.

When you limited the cyclic throw did you still have blue LED ?

[DannyvG]

I only looked at the blue light when setting the 6 degree of cyclic. So I dont know what light it gave when setting the cyclic limit.

[huckzilla]

I tried a servo arm that moves each ball out 5mm. So now they are 18 mm from the center of the servo as opposed to 13mm. It solved the problem but the resolution is awful. The servo barley moves and the swash pitches all over the place. I will try more stuff in the AM. Any more suggestions are appreciated.

I also tried a 15.7 mm spaced JR servo arm. I got blue light at 6 degrees dead on but still over drove and stalled that 1 aileron servo although it seemed better than at 13.7mm

Thanks again

[bobloblaw]

I'm using the JR flybarless head and have my balls 15 mm out from the centre on my servo horns.
I cannot get to a blue light on step J without my elevator mixing arm binding really badly (see this thread https://www.helifreak.com/showthread.php?t=267346). I just get to red when binding occurs now and this means about 9 degrees aileron deflection and 7 degrees elevator.
So, I have settled on the idea that the Vibe 50 servo positions are not optimal for flybarless use (I have mates using Vbar on their Vibes and they feel the same way) however mine seems to be flipping and rolling pretty well and I'm happy with how it flys now.

[ollie2893]

If you get adequate collective throws (the famous blue light) but you cannot get adequate cyclic throws, then your problem are the attachment points of the links to the outer ring on your swash. You would need to reduce the diameter of that ring - any which way.

[huckzilla]

I tried multiple different servo arms and ball link distances with no real luck. Specifically 12 mm, 15, mm , 17 mm and 18 mm. These produced various combinations of binding or poor cyclic throws and a stalled aileron servo. As far as the ball links on the swash the only ones I can adjust are on the inner ring, they can be made shorter. I will give it another crack tonight, this is really annoying.

Again it seems the compromise may be way reduced collective or cyclic. Hopefully I can work around this.

Thanks guys

[ollie2893]

You cannot solve this problem with servo arms. If your arms were too short, you would not achieve the necessary pitch travel. But this is NOT your problem, as I understand it. So your arms are fine. The diameter of the outer swash ring is too large and as a consequence, the plate doesn't tilt enough. Even if you cannot fix your current swash, remember that these things are - within reason - interchangeable between different birds. Take your bird to the LHS and try different plates. Or call your favourite online shop and ask what other plates there are with matching ID but smaller OD. I am confident that you will find one that suits. (You can also consider 120* plates.)

[huckzilla]

Thanks I do have the set up for a 120 swash at home.

[ollie2893]

Actually, the 140* swash is an interesting consideration. You say you have problems with your aileron throws? But on a 140* swash, the two aileron attachments point on the outer ring are nearer together than the distance between an imaginary line drawn through those points and the attachment point of the one elevator servo. That is, do you not get even bigger problems with your elevator throws? Put another way, I suspect that a 120* swash may make your aileron problems worse (unless its outer ring is less in diameter than that imaginary line is long).

[huckzilla]

The swash is the same for the 140 you add longer front ball ends, for the 120 they are shorter. Here is a pic of the stock vibe swash.

[ollie2893]

Hm ... I won't pretend that I understand from that picture how the assembly is supposed to work (the "wings" on the OR look like they might actually be 90*). But "shorter front ball ends" on the 120* sounds like the right way to go.

Incidentally, what is the advantage of a 140* swash arrangement over 120*?

[huckzilla]

Here are some better pics on 140ccpm the front ball links are longer . Honestly not sure what he benefit is.

[ollie2893]

OMG - I can see your problem right there in those pictures. Compared to your garden-variety eCCPM head, these aileron balls are MILES away from the elevator ball. Again, I had thought this arrangement would give you more trouble along the elevator axis than across the aileron axis. I cannot see but I am guessing that you must have some serious bell cranks on the aileron push rods? How else would you otherwise ever attain any reasonable throw? Unless perhaps the ball ends on the grip holders are REALLY close to the grips...

EDIT: Just checked pic #3 - yes, the links are REAL TIGHT on the grips. That's how your head translates such little swash movement into reasonably blade angles.

EDIT: Incidentally, I thought that pic #3 showed a FB head. But there is no FB. What's that mixer for on the red blade grip?

EDIT: Do I read this right: for pitch moves both rods lift the mixer, for cyclic moves only one does? Meaning that for cyclic moves, only 50% of the travel is passed up? Why? Should you not be getting rid of that mixer?

[huckzilla]

That is the JR FBL head, I actually use the RJX head. ( see below) I agree mixer arms on a FBL head are kind of dumb. Regardless my swash set up is the same.

All 3 Swash arms move for collective pitch and elevator cyclic. Only the front two move for aileron cyclic.

[huckzilla]

pics moved below

[ollie2893]

I am getting more and more bewildered by all the pictures, which appear to be of different helicopters. Let me see whether I get this straight. Your Vibe with FB would look like the last picture with the orange fuel tank? That bird would have a head very similar to the JR FBL head you showed, with the mixer EXTREMELY close to the grips? You replaced this head with the RJX head which, compared to the JR head, has the link attaching much further out in front. Your bell cranks are amazingly small. It looks to me as though the stock Vibe translates really small deflections of the swash plate into large movements on the grips. Have you tried to replace the RJX blade arms with the JR ones? I think you will need to get the link as close to the grip as you can. I am guessing that given your present collective travel which results in +/- 10* on the RJX, you would get much more than 10* on the stock head?

[huckzilla]

Sorry for the confusion This is my head on another guys Vibe 50 also with a 140 ccpm Swash. My servo arm geometry is the same as the heli below:

[ollie2893]

Ok, for me the relevant pictures are this

and that

Just look at the distance between the link arms in the two pictures. The JR is as close to the grip as is somehow physically possible, the RJX seems 3cm out in front. This is a HUGE difference in leverage. You need to get the RJX arm closer to the grip. If possible.

EDIT: Have you checked the RJX web site? These arms are clearly easily replaced. So perhaps they offer different arms to achieve different geometries?