CCPM cyclic and pitch interaction

[DarkHorse]

Has anyone got a good step by step instruction to reduce cyclic interaction with pitch?

I'm being a little fussy but I want my heli to sit in GE without bobbing (aka popping) up and down in altitude caused by very small +/- changes in blade pitch (overall swash plate hight) as a result of CCPM cyclic interaction.

As I understand it the problem is a mechanical phenomenon due to the way 3 servo horns move in relation to the swash plate. These small geometric differences tend to be more noticeably on micro heli's. The physical servo size makes it almost impossible to position the servos to eliminate such errors.

Ideally I could choose (or work out) a setup scheme so that cyclic interaction only caused a small increase in blade pitch (a desirable mix anyway). Or do I just use a radio mix to compensate?

Hornet II CP setup references:
http://hometown.aol.com/mikeflyz/setup1.html
http://www.deeteeenterprises.com/NS.ms_hornet.throttle-pitch-setup.php
http://www.ericlarsonrc.com/Heli/Equipment/HornetII2005/HornetII2005.htm

[DarkHorse]

Hey, I shortened the Bell Hiller mixer arms (by 1 full turn) and the problem is much less noticeable. Few!

[MoonBlade-X]

DArkHorse....

to have no cyclic-pitch interaction, u'll have to rip out all ur servos and do them up again Tale a look at Lowell Foo's RR gallery: http://www.runryder.com/helicopter/gallery/24912/ U need to have all the links straight up and at right angles to the swash.

When Ifirst saw ur pics, I wanted to tell u to change them out already... but i tot it'll be a drag and pain.... so I held back.... Anyway... have a non-interactive layout really makes a lot of difference... Shoe-goo ur servos... 3M tape will work nice with some de-greasing remover... but then the tape always "gives" resulting in a not so "solid" and "sharp" /"crisp" feel to things...

[DarkHorse]

Hi,

> shortened the Bell Hiller mixer arms
This was probably being optimistic , looking at the assembly I'm not convinced it helped yet.

> Lowell Foo's
His futaba servos are quite a lot smaller than my MS 22s and even if I cut the tabs off I don't think they will position 100% where they are required.

> u'll have to rip out all ur servos and do them up again
Yea I've done that a few times already . With all servo's and links the same, the best I can get is nearly there except for a slight vertical angle on the bottom of the links being away from the main mast. Any further interactions will have to be radio mixed out.

Thanks

EDIT: I have a fix to reduce servo foot print size... but it involves removing the back of the case from the MS-022 servo...

[MoonBlade-X]

nO daRKhORSE,..it has nothing to do with size... if i'm not mistaken the MS servos are HS-55s re-badged... in that case it should work... because i've the done the same and i'm on hs-55s as well.. the whole point is to follow the same layout... with the finre adjustments slightly different.. u have to get the links straight.. to do tht.. the rear two servos will sit slightly out of the CCPM tray....

[Sao]

Missed these threads

Did you get it sorted yet DH?

Moonblade is right though you need to get the servo and links inline with the swash to take out as much interaction as possible. If they are going to be out then they all need to be out by the same amount or all lined up perfectly.

I gave up trying to get it spot on with the stock servo mounting method so went for the metal servo mounts and i have to say it is a vast improvement for a margnal weight gain.
Using the mounts you also raise the servos up a bit so the front one doesnt hit the chassis at full deflection meaning you can get a bit of extra travel out of it.

[DarkHorse]

Hi Sao,

I'm compromising whilst learning about this new setup. Taking it slow and steady indoors and haven't had an incident yet.

I think for indoor hovering, any cross interaction is now undetectable (with small cyclic movements). The bobbing and popping (I think) is now down to air turbulence in a 10x12ft room. It seems less floaty on the GE cushion than my Piccolo FP (below 2ft). The Hornet tends to dip a little whilst I hear the blades gargle in turbulence (wall blow back?). Also this may be down to the difference in blade loading with a symmetrical CP blade verse an FP blade with a washout twist. Not too bad just unexpected.

Servo layout:
> then they all need to be out by the same amount
That's what I'm going to live with.

I tried several orientations but I'm always a few millimetre out of alignment. The MS-022 has a large waste of space at the case rear which could be discarded (~4mm). At the moment I have a compromise that works and only looses a very small amount of pitch at full cyclic Ail+Elev.

MS-022 vs HS-55s ? The servo's are very close in dimensions:
HS 55 - 22,8x11,6x24 or 23 x 12 x 24mm
MS-022 - 24x11x24
Both are displayed here http://www.szanmodell.hu/servo.htm


> Using the mounts you also raise the servos up a bit
> so the front one doesn't hit the chassis
I noticed that issue and can trim the servo horn but not sure if I need that extra cyclic yet.
Just binding front servo at +10 degrees pitch when setup:
inner servo horn holes, swash Elev -46%, 100% dual rate, 100% end points, +10 degrees pitch

Using inner servo horn holes all round for high resolution.
Mid stick = 50% Pitch = 0 degrees

Swash Ail +46%
Swash Ele -46%
Swash Pit -40% gave me about +10 degrees to -15 degrees of pitch

I have more neg than pos pitch, +10/-15 degrees of pitch ?

[Sao]

Quote:

Just binding front servo at +10 degrees pitch when setup:

Is that when you are holding in forwards elevator as well? I found when i had full pitch the chassis restricted movement on the elevator and I couldnt get a fast enough flip, with the ally mounts there is plenty of movement.

If you have more negative than positive then you need to play with the links and get it in the middle. sounds like you need to alter the swash position and then alter the links to the blade holders to dial in the correct pitch range.

The bobbing and popping you described can well be down to turbulance in a small room, it could also be the head binding under load, Check that the flybar carrier can freely slide up and down the two metal pins from the headblock. I grease the pins on my head to be sure that all is free.

[DarkHorse]

> alter the swash position and then alter the links to
> the blade holders to dial in the correct pitch range
I followed the instructions for suggested link lengths.

> chassis restricted movement on the elevator and
> I couldn't get a fast enough flip
I expect I'll run into have the same problem.

Thanks for the help, I can see what's going on, altought I dare say I'll go around this loop a few times. At least I know what the crack is and will let it all run round in my brain... then get motivated to implement a fix once and for all.
Here's my current usable if not so perfect setup so far.

[Sao]

Quote:

I followed the instructions for suggested link lengths.

thats one problem solved then

The links in the head from the blade holders need to be trimmed back to get the required distance as even the short ball links are too long. Also the bell hiller mod does change the required lenghts for these links from memory.

As you can tell from looking if those links are too long then you will have more negative than positive.

Heres how i set up my hornets be they bell hiller stock or duzi'd up.

Set the servos to mid stick, get the flybar carrier in the middle of its movement (i do this by measuring the totoal travel and then halving the figure, selecting a suitable drill bit or spacer and placing it under the flybar carrier to set its mid point. Now adjust the links from the servos to the swash to get this all sat nicely.

Now check blade pitch, it should be 0 Deg, if it's not then change the links going to the blade holders, you will probably have to trim 1-2mm off to get them close enough together, when this is set and you wich to adjust the blade tracking do NOT do it with these links, use the long ones from the swash to the bell hiller mod. This is as per the duzi metal set up as the links to the blade holders are fixed to maintain correct geometry in the bell hiller (well at least thats the way i understand it)

I'll try to take some measurements of my set up later from home

[DarkHorse]

That's a great description, thanks Sao.
Makes complete sense, nothing can stop me now...

> adjust the blade tracking, do NOT do it with these links (to blade holders)
Didn't know that bit.

Instructions guide lines:
"links going to the blade holders = 16mm"
"long ones from the swash to the bell hiller mod = 34mm"

After you post some guide measurements I'll have another stab at it.

Thanks

[DarkHorse]

Thanks,
I'm happier with this setup now. I removed servo tabs and took the back off the farthest servo. Pitch is now even +/-15 degrees, softened to +/-10 degrees:

[MoonBlade-X]

U must be a happy camper now.....

I find this setup flies the smoothest ... I can go hands free longest on this one....    

[DarkHorse]

3 rd time lucky... I sure am!!!  
Haven't really tested it in anger yet, as I've been distracted messing about with little nitro cars recently.

[MoonBlade-X]

I took a break on Saturday and had a go at my friend's Half-8..... it's half the size of a 1/8.... electric... from kyosho... buggy's rock!!!