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E-flite . Next D . Fast Lad Performance

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Main Discussion > CCPM: P-mixes or ATVs
 
 
choppertime
Senior Heliman
Location: Virginia Beach

OK, I couldn't get my grandmother to use a toaster either cause she insisted it was easier to do it in the oven.
12-05-2003 Over year old.
 
 
Optech
Key Veteran
Location: Vista/Oceanside, CA.

"If your not going to do it right, then its not worth doing"

Mike

Viva La Airtronics!
12-05-2003 Over year old.
 
 
Dr.Ben
Elite Veteran
Location: Richmond, VA, USA

Mike,

I still hate using the ATV's, but there is no other way to exactly match the total throws on the servos. I was able to use pmixes alone when the servos were new and closely matched, but after some wear and tear, the matching had deteriorated to the point that I needed the ATV's. Trying to correct the problem with pmixes alone created unresolvable problems with having the swash go in and out of track multiple times across the collective range. It drove me nuts in flight as I tried to do a perfectly straight climb out over the cone. As I'm sure you know, anyone who thinks you save a bunch of total bench time with an eCCPM model vs a mCCPM hasn't gone through all the legwork required to get the eCCPM set up as interaction-free as possible with little or no extra crap in the radio. There's no free lunch here, as most everone will agree.

HiTec has done a good thing. Sadly, the last time the Steve Helms brought up the subject of programmable servos with Futaba JP, it wasn't on their list of priorities.

Ben Minor
12-05-2003 Over year old.
 
 
choppertime
Senior Heliman
Location: Virginia Beach

I checked out some info on the multiplex. Thats a good deal for the 9 ch Tx with frequency synthisizer @ $419. It appears to have the same type of programing as the Stylus though. There wasn't enough detailed info on the web site.
12-06-2003 Over year old.
 
 
King Cobra
Veteran
Location: Virginia. USA.

Dr Ben

The EPA ( Stytlus ) = ATV ( Futaba , JR )
CP-EPA ( S ) is a Swash ATV + Pitch mixing addition to 9 others mixing .
Perhaps with the faster servo the less( or not any ) interaction during transition.

C.T
12-06-2003 Over year old.
HOMEPAGE  
 
 
choppertime
Senior Heliman
Location: Virginia Beach

Some how I think the industry will be heading back to mCCPM again. All the marketing will swing back in that direction. I might actually fix my excell pro back up again. Now that's a control system. Just need to get a hold of a tempest head for it. I could use a raise right about now. Will the promotion gods please hear my cry.
12-06-2003 Over year old.
 
 
choppertime
Senior Heliman
Location: Virginia Beach

Thanks Chris for that info. I would assume my servo's aren't fast enough as they are the standard 9202's but I'm still trying to hit the lotto to fund my fun.

Are we going fying today or what?
12-06-2003 Over year old.
 
 
King Cobra
Veteran
Location: Virginia. USA.

Mike

mCCPM servos speed will always run behind eCCPM, not much fun on the quick collective . WHAM BAM style !
But it is nice to have as many helis and difference set up.

C.T
12-06-2003 Over year old.
HOMEPAGE  
 
 
choppertime
Senior Heliman
Location: Virginia Beach

Why not? If you put a big servo wheel on the mCCPM setup with the same servo's the speed will be the same right. If not, please explain.
12-06-2003 Over year old.
 
 
King Cobra
Veteran
Location: Virginia. USA.

mCCPM on 90 machine need servo with more torque, so there go your speed. You could however use a fast speed servo on a 30 -50 size heli with adequate torque. But I don't like those 2000 rpm.

C.T
12-06-2003 Over year old.
HOMEPAGE  
 
 
Vinnie
Senior Heliman
Location: Miami Beach, Florida

umm

I'm on my 4th Fury now and to be honest, every single one of them had a perfectly level swashplate in all collective positions after mechanical adjustments. I used the Miniature Aircraft swashplate leveling tool (simple plastic piece that slides over the main shaft).

I am running Futaba 9252s.

Are you using the big wheels? Are you drilling your own holes or something? I find it hard to believe that with the right hardware you are needing to resort to PMX or ATV.
12-07-2003 Over year old.
 
 
Dr.Ben
Elite Veteran
Location: Richmond, VA, USA

Vinnie,

Go back and check those models at around 1/2 dozen points in the collective range after the servos have had several cases or more of fuel through them. I promise you the swash won't still be in perfect track. I've seen 9252's go out of perfect match after just several gallons, and servos from the other mfg's are no less prone. It's all about a carbon wiper pot; the part wears, and centering and total throws change. Also, it's not all about keeping that swash dead level. Interaction also concerns what is occurring when cyclic commands are introduced. Go to the higher or lower extremes of collective range and enter a pure ail or ele command. If the model has any time on it and has not be recently retracked, I virtually guarantee you see interaction bewteen the two cyclics. Unless you want to replace servos after only a few cases of fuel, you have no choice but to use the radio to get the servos back in line. There will be some interaction in any case, because rotary servos are being used, and ball links on the servos are moving further away or closer to the centerline of the servo with extremes of collective throw. Even the finest eCCPM models have these liabilities. It is the best designs, though, that minimize the manifestations of these liabilities.

In reality, the trick with any eCCPM model is trying to determine how much error in the system you can tolerate before flight performance really suffers. For some sport flying where the majority of the control inputs are broad and using up much of the collective range back and forth, you won't notice subtle changes in swash tracking along the way. Try some FAI where you have to have the model slowly climb perfectly straight out over a cone while pirouetting, and a little mistracking in the swash can drive you nuts. In point of fact, the FIRST place I notice eCCPM "issues" is in precision rolls. Formerly well tweaked swash phase compensation mixers gradually go all to hell. I have to remember to recognize the problem for what it is rather than try to retrim the whole model.
12-07-2003 Over year old.
 
 
King Cobra
Veteran
Location: Virginia. USA.

With the exeption.

For mCCPM Airtronics 94758z's is the cure.

C.T
12-07-2003 Over year old.
HOMEPAGE  
 
 
Vinnie
Senior Heliman
Location: Miami Beach, Florida

blech

Dr. Ben ugh that sounds like crap!

So after a few gallons everything is going to turn to mush?

I used 94758Z Airtronics in my latest Tempest FAI, is this going to help? How do you program them? They didn't come with anything except the mounting hardware and arms.

Oh yeah and the wires are short on those servos, I needed two extensions to fit them on the Tempest (elevator servo and 1 aileron servo).
12-07-2003 Over year old.
 
 
KC
Elite Veteran
Location: WA

for what its worth, heres how I did my fury....its got 9252s with the big futaba wheel arm

I had 10 big wheels laying around for this.....

I centered the left stick at 50% made sure the collective output in the pitch curve was 50% too (duh ,but it had to be said)

no trims, all atvs at 100%

then I matched each wheel until I got as close to a right angle setup for all three of the servo wheels as I was going to get

then I USED SUBTRIM to make the 1-2% change that it took to have them at a right angle, that much subtrim isnt going to hurt anything.

end result, no drilling for a "perfect" servo arm hole that I probably couldnt do with my shaky hands anyways.

when I go to trim the machine, I use the trims in flight to get a feel for where it needs to be "trimmed", then I do it mechanically after landing

(this is time consuming, and I'm lazy, but it is worth the effort if you are serious about your heli performance)

to mechanically trim the aileron, I twist the front two rods opposite to each other. for the the elevator, I twist the front two rods same direction.

what usually happens is there is a small shift in the collective pitch position that will probably affect your zero stick, so I then twist the p-rods leading from the swashplate to the mixers for the flybar/blade grips to get the zero center (and whole pitch curve) back.


.....or you can chase it around electronically as the servos wear out, which they really do, but its nice to know if its mechanically sound before masking things up in the radio.
12-07-2003 Over year old.
HOMEPAGE  
 
 
Vinnie
Senior Heliman
Location: Miami Beach, Florida

hmm

What I have discovered when building the Tempest, is that it is always possible through careful selection of the servo arm position, to get the large Futaba wheel into exactly a 90 degree angle (and for the Tempest, the necessary 92.5 degree angle for the elevator servo).

This became very clear when I tried each servo output spline position and compared it to the template tool that comes with the kit.

Sub trim is never needed.

But what I understand from Dr.Ben and DavidH is that after the servos have "worn in" (?) a little bit the calibration changes, and certain positions of collective have differing non-zero levels of cyclic interactions (?).

What is the behavior of the potentiometers in the servos? Do they get a little messed up in certain positions or something? Maybe there are servos that use an optical system instead of mechanical pots?
12-07-2003 Over year old.
 
 
Dr.Ben
Elite Veteran
Location: Richmond, VA, USA

Vinnie,

For all intents and purposes, what you said about the servo pots wearing in is true. We sit around hover putting thousands of minute corrections in in each flight or climb and descend with similar amounts of control input each time. Back and forth, back and forth...............that little wiper moves inside the pot a zillion times in the same area. Given that fractions of a degree in centering and total throw can cause the swash to go out of track, it is fortunate that our set ups stay sound as long as they do. Optical stuff would be nice, but the mfg's don't seem to be interested in that kind of R&D at this point.

The degree of sophistication of our equipment is still remarkable. Think about it. Three servos driving the swash at once with ZERO, NADA, NONE feedback between the servos about where each lies along the travel range WRT each other, yet we can get an almost perfectly level swash with little extra fiddling beyond a sound mechanical set-up. Really quite amazing.

C.T...........stay tuned. Futaba and JR are releasing some servos that are so darn strong and fast that if you got a finger stuck in the collective yoke, they'd probably take it off at the stump .

Ben
12-08-2003 Over year old.
 
 
KC
Elite Veteran
Location: WA

Vinnie

Subtrim isn't bad. Most every Fury is built to the instructions with big servo arms and 100% ATV, so subtrim is not going to affect the servo travel range in small amounts.

here's a good general rule of thumb for using subtrim that won't get one into trouble with control throw range:

max subtrim (in percentages) < {ttl atv available by radio -atv used} / 2

lets assume your radio does 150% atv, you use 100% atv, so dont exceed 25% subtrim.

disagree? you can prove this to yourself with the equipment you own before your very eyes. the subtrims are an aid that can cut hours off of construction if used intelligently.

stick with me kid, I'll have you farting through silk shorts.
12-08-2003 Over year old.
HOMEPAGE  
 
 
Vinnie
Senior Heliman
Location: Miami Beach, Florida

R&D?

What R&D? Optical replacements for pots have been around for a LONG time.

I remember I had a wah-wah pedal with a pot, and then they came out with one that used an optical sensor.

As for cost, an optical system would use fewer parts and be more precise. Furthmore it would draw less current.

Hypothetically, if servos could perfectly measure and control the position of the output spline even with wear, would all problems in eCCPM systems be solved?
12-08-2003 Over year old.
 
 
Vinnie
Senior Heliman
Location: Miami Beach, Florida

STM

KC sub-trim isn't bad but what I was saying is that it is always possible to get perfect servo output placement with the Fury and 45mm Futaba wheels.

In other words, if you have to use sub trim on new servos when building a Fury using the Futaba wheels, you made a mistake.

Not sure about other vendors but I do know for a fact that the stock Airtronics 94758Z servo arm can NOT be used to get the 20mm distance necessary for a Fury and furthermore it is not always possible to get to the 0.0 degree point, or the 2.5 degree point (Tempest).

I used the Airtronics Extra Large Servo Wheel for Standard Servos, and I know for sure that even the farthest holes (there are only two) are not 20mm and also they don't line up depending on how the servo is installed. I had to drill my own hole. Again this is for a Fury. Note if you use these servos in a Fury the top two will require extensions.

While we are on the subject I would also like to point out that if you use the Airtronics 94758Z servo on a Fury, the elevator servo will have to have some of the servo case trimmed in order to seat correctly against the frame. Specifically, the raised rib on each side of the case, in between the bolt holes, must be shaved down a bit (compare with a Futaba case).
12-08-2003 Over year old.
 
 
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