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Gyro Hobbies . E-flite . Next D

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Main Discussion > CCPM?????
 
 
HeliWhacker
Senior Heliman
Location: Childersburg, AL.

That could be it, I am using the servos that came with the radio.

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05-18-2004 Over year old.
 
 
jvsjvs
Senior Heliman
Location: Best, The Netherlands

Interesting. I personally am very much in favor of mCCPM, since there is no interaction if setup right.

I always get the message about eCCPM being stronger on the cyclic and collective. This is not always true. In typical flight this is definitely not the case, since you typically of course roll, nick and control the pitch, so three servo's are effectively controlling three movements. This is exactly the same for mCCPM

However, to reduce the interaction (hide the non-linearity) you typically reduce the ATV of the servo's quite a lot for eCCPM systems, and use longer arms. This makes it all less non-linear, but also reduces the effective force the servo can apply on the swash! People often forget about that. Furthermore, it reduces the resolution of the control system a lot. There are other disadvantages to eCCPM as well.

A good mCCPM setup wit a strong pitch servo can do pitch pumping just as well as eCCPM.

When I find the time, I will better argument my views on my website with pictures and mathematical argumentation.

Best regards,

John
05-19-2004 Over year old.
 
 
ASAT
Senior Heliman
Location: Pleasant View Ut.

Toad - how you doin bro? This is Lou from up north - when did ya get the Fury? Do you like it better than the Treppie? Hope all is well with you, has the wife joined ya yet? Take care, Lou
05-19-2004 Over year old.
 
 
G.Man
rrProfessor
Location: Northants, but soon to be Nicosia, Cyprus

jvsjvs

well done

The collective servo is the key on mCCPM and with airtronics 0.06 uber servos I can't see any eccpm setup being better...

Yeah you could use 3 on eccpm but that would just show the interaction more



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05-19-2004 Over year old.
 
 
Blackrockminer
Heliman
Location: Somewhere else

Galifrey,

I think you might need to check your 9Z radio I'm using a 9C with
9252 digitals and there is no interaction smooth as silk no matter how fast I work the pitch
05-20-2004 Over year old.
 
 
G.Man
rrProfessor
Location: Northants, but soon to be Nicosia, Cyprus

Ah okay, I'll return it for service then



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05-20-2004 Over year old.
 
 
HeliWhacker
Senior Heliman
Location: Childersburg, AL.

Alexander,

I tried that on my crappy xp662/ on a venture 30.
fore/aft and left/right has ZERO effect on the swash up/down movement looking where the swash bearing contacts the main shaft. No matter where the collective is set. Also, the swash stays as level as the eye can see over the entire collective range. I have looked at this many times trying to figure out what theyre talking about.

I have noticed every person claiming interaction in eCCPM has also reffered to a Futaba radio.
Maybe its a futaba thing??? .

Anybody with a JR or Airtronics have any observations on this?
05-20-2004 Over year old.
 
 
KC
Elite Veteran
Location: WA

you guys are all talking about two kinds of "interaction", the design interaction and the interaction that comes from use.

the first kind of interaction is ok to deal with, its stable and can be corrected by memorizing the handling qualities of your heli and precorrecting with the thumbs or radio.

the second kind is not consistent and is costly to fix.

if your eccpm has no interaction now it just doesnt have enough time on the servos yet...simple to prove to yourself, you'll see it in time, all things wear out.

most servos still use brushed potentiometers, so you will see interactions after a few hundred flights in the best of conditions with eccpm,

3 servos being asked to do one thing is like working with the govt, nothing gets done all that well, physically impossible for all those servos to be the same over time for any one given control command.no two servo potentiometers wear at the same rate

you'll see it with time, thats relative, to me 300-500 flights is a couple of months, so I dont like eccpm much, cause I'm chasing the second kind of interaction more than I care to.

not to mention what it costs (in time and money) to replace 3 servos when 1 is bad to the core.

the life-span difference between std mix and eccpm may "disappear" with optical potentiometers when they come around, but those will just make std mix that much better too.

the eccpm machines competing in international f3c are no surprise, hardly any of those machines have more than 200 flights on anything in them.

but for cherished models with hundreds more flights on them than that, and servos that cost 80-100.00 a pop, eccpm can be a costly choice.
05-20-2004 Over year old.
HOMEPAGE  
 
 
G.Man
rrProfessor
Location: Northants, but soon to be Nicosia, Cyprus

To understand interaction you have to understand how radios work...

Firstly for eCCPM the radio has to process 3 channels for any 1 control movement... With a fast CPU modern radios can handle this without much of a problem, but obviously 1 channel will always take priority, and the order is...

For a collective change the pitch servo gets priority, and for a cyclic change the corresponding cyclic servo takes priority...

Now, the next part of the equation is the transmission and recpetion of the data...

The data from the radio is effectively "streamed" quite quickly from the radio to the RX the processed in the RX and sent to the servos.. Again there is always a sequence for streaming and reprocessing of the data, this results in one servo always being slightly ahead, and 1 servo always being slightly behind... Usually this isn't noticeable, but with modern fast digital servos and quick pitch pumping movements the swash will effectively tilt slightly in one direction..

If your heli is hovering level and you pump the collective up and down briskly the heli will start to tilt and start a sort of low speed flip...

This exagerrates the problem and a pilot rarely pumps the collective up and down in a hover so it is not easy to see, however, when doing some types of manouvers the pilot will see the heli start to move in an undesirable fashion and fly around it, thinking its just a required input for this type of manouver...

It should be made clear that to spot this you would normally need to fly 2 identical helis back to back to see how the mCCPM and eCCPM behaved differently (say 2 sceadu's one mCCPM and one eCCPM)...

If you only fly eCCPM machines you will probably never notice or care



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05-21-2004 Over year old.
 
 
G-DAVE
Veteran
Location: Tyne and Wear , England

just a thought ??

Like the discussion - never realy thought about it - tell me if I'm wrong - does it mean when you use the very quick digital servos this lag would be more noticable than if you used 3001's for example ??
Dave
05-21-2004 Over year old.
 
 
flmgrip
Veteran
Location: Irvine, CA, United States

Galifrey, i believe you are wrong. the delay of servos (if at all) is caused by very slight differences in the speed of each servo on the swash. and that normally can be corrected easliy by mixing the error out... i can pump my heli up and down all day long with out doing a flip...
the processing speed of the tx and rx is way faster than any servo will ever be...
05-21-2004 Over year old.
 
 
TMoore
rrProfessor
Location: Cookeville, TN

Servo Dance on CCPM

The fastest systems are going to be pure PPM/FM. If you are using an original 9Z on PCM you are going to see the servos outrun the collective commands. PPM/FM will help to overcome this issue. There is video on this forum that shows this happening with a 9C, search for it. The new 9Z uses a different calculation algorithm to overcome this.

The Airtronics Stylus on PCM running 3 94357's on collective or 3 94758's, both on 6.0 volts unregulated, won't do the dance. If there is a servo lagging it is a simple matter to match the speeds instead of messing with the EPA/ATV adustments. This function is called CP-S Delay.

PCM forces another layer of encode/decode since the servos are purely analog devices and can't use the native PCM format to command their position. Despite the "Digital" moniker, the servos are still analog. A more correct term is Super Servo. Kind of like the "e" versus "m' BS.

If we were still using servos with a frame rate of 60 cycles/sec most modern radios and some older ones would work fine. Even a 512 system on CCPM with standard servos is very usable. Only the SS's can tell the difference in 1024 and 512 resolution. One reason the dance is so obvious on certain radios is the servo loop time from command to execution can vary depending upon what you are doing. The more channels that have to be updated in the data stream the more clock cycles that are needed at both ends to accomplish the task while running PCM.

It is hard to beat a well setup mechanical collective system if the modeler understands the setup issues.

Terry
05-21-2004 Over year old.
HOMEPAGE  
 
 
G.Man
rrProfessor
Location: Northants, but soon to be Nicosia, Cyprus

flmgrp

if thats what you think try swapping the servos around and strangely you will find that its the same position servo lagging each time not the same servo

Tmoore

Nice post, better explained than me



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05-21-2004 Over year old.
 
 
JKos
Elite Veteran
Location: City of California in the state of Maryland

Galifrey,
> If you are using an original 9Z on PCM you are going to see the
> servos outrun the collective commands.

As TMoore stated, the original 9Z is notorius for problems with eCCPM setups. Which version are you using?

I've set up four helis with eCCPM in the last year and have yet to have one iota of a "swashplate dancing" issue with full and fast collective movements. That was with two different radios, the Eclipse 7 and 9C both PPM and PCM.

- John
05-21-2004 Over year old.
 
 
sharam
Elite Veteran
Location: Northern California

Great discussion guys, thank.

Question for those who clearly know a lot more about this than I do - how much does the receiver enter into this? I am sure that some receivers are more advanced in their signal processing and capabilties than others and I was wondering whether using a 309 synthesizable receiver (top of the line Futaba) will have noticeable advantages over a regular 9 channel PCM Futaba receiver.

Yes, I have heard about the 309 "not being suitable for heli applications", so let's not go down that path please.
05-21-2004 Over year old.
 
 
heli1man
Senior Heliman
Location: Chautauqua Lake, NY

no huge diff

Sceadu flyer,
To answer your question
There is no big difference in the feel of eCCPM and mechanically mixed set up. I have my eco 8 with eCCPM and the Raptor with mechanical mixing. I am not into 3D yet and may never get there as I don't get as much stick time as I would like to......Well at least I do with that kind of stick time Just set it up using the MMix and don't worry about understanding the eCCMP if you're new to this hobby. There are no benifits you will gain from eCCMP at this stage. I would Imagine there are those who fly 3D that have a different opinion. My Eco flies better with eCCPM only because of the Ikarus design flaws using their sliding pitch tray for MMix. The sceadu and Raptor do not have these design flaws.I was also able to save a little weight going eCCPM with the eco 8 too, and weight is everything to an Electric, that is the only reason I did it. As a matter of fact before I purchased the Raptor I was going to get the JR Venture 30 until I found out it was eCCPM only. So I bought a Raptor and have never looked back! So anyway stick to the MMixing and have a ball!.....................Lots easier to set up too.

Bill

Eco 8 Brushless, MS composits Raptor30v2 39TT 550TT carbons Shogun 400 Brushless 3 cell lipo.
05-21-2004 Over year old.
 
 
rcnuts
Veteran
Location: Millersville, Penna

I am not going to attempt tp give technical descriptions on the differance of standard and ccpm, or eccpm. Heli enthusiests here have done a much better job of that than I could. I would prefer however, to give my take on the actual "feel" of flying the 2 differant swash setups, more from a pilots point of view. I have owned and flown both, as far as flying goes, there is not much differance. Some here will complain of "interaction" that occurs with ccpm. I have never found that to be of any significance. Yes, I DO most definately see and feel a slight interaction, but what the hell, we do fly in the wind, right? Flying in the wind will cause you to compensate to keep your machine level, so forget about interaction. From an engineering point of view, I most definatley prefer ccpm, or eccpm. 3 servos pushing on you collective function at the same time just seems like a better idea to me, and I do tend to hammer the sticks. Just my take on this!
Harris,

Hooligan, at large
05-21-2004 Over year old.
 
 
KC
Elite Veteran
Location: WA

again, let me reiterate something here, there isnt much difference between eccpm and std in the first few hundred flights.

in eccpm you are asking 3 separate devices to provide one output....intuitively, this isnt going to be as precise or consistent as one device per control.

and in practice it is proven over time to not be as precise/consistent as std mix after those few hundred flights, do not look at the world champion f3c machines with eccpm and think it will work for you just as well, the servo sets in those things do not have the hours or abuse that mortals can put on them.


servo 'ganging' works well on fixed wing models because you are moving a control surface that is hinged on one axis only...a swashplate rotates on two axes and slides up and down, showing every difference or weakness of the servos.

if you have ever mechanically trimmed a ccpm machine, you know that it is almost a study in mathematics to get a precise mechanical trim without using the trim levers! why do that? trim levers can be bumped and positions can be forgotten/lost even if you write them down....and a lot of radios electronic trims do not mix for eccpm.


there are really only two interactions to consider on any control system

-design interaction: consistent, correctible. best example would be the physical geometry of the controls. you can mix it out or memorize its effects and fly through it.

-time interaction: things wear out, the rate is not consistent or predictable in most eccpm systems. best example would be the potentiometers in servos, these are the main thing to watch in a servo.

"I dont notice much difference".... you will not really notice the difference until you compare the two side by side, trying to fly the same maneuvers as best as you can over time.

"I still get interaction with std mix" there are two effects that are commonly mistaken as interaction that have been around before eccpm became common.

-swashplate timing: this is noticed when the control outputs always happen in a direction that is a few degrees off of the command input, say you gave left cyclic and the heli always went a little forward too....this can corrected mechanically or electronically.

-"rotational interaction": I have no clue what to call this effect but most clockwise rotors will want to punk out rolling right on an outside loop...I believe this is due to the difference in mass distribution from nose to tip and across the helicopter....some f3c oriented pilots will correct for it in the radio with swash mixes, most pilots just fly through it.

which to choose?

eccpm: if you are not concerned about costs or interactions or if you dont care whats what. eccpm takes a little more set up knowledge to squeeze the performance from, but it can be done and works great for 3-d.

std mix: if you want to mix and match servos, if you like running 150% atvs. best suited for f3c/ pattern and scale, permits more radio mixing options and easier timing for flybarless heads. Alan Szabo does some pretty good 3-d with it too.
05-21-2004 Over year old.
HOMEPAGE  
 
 
G.Man
rrProfessor
Location: Northants, but soon to be Nicosia, Cyprus

Quote 
As TMoore stated, the original 9Z is notorius for problems with eCCPM setups. Which version are you using?


Come on, do you really think I would use anything less than the WC2???

Quote 
I've set up four helis with eCCPM in the last year and have yet to have one iota of a "swashplate dancing" issue with full and fast collective movements.


Fine if you are happy stick with it...

Quote 
and a lot of radios electronic trims do not mix for eccpm.


Which ones are those?

Trims only move the stick position (physically or electronically and as such the electronics allow for it with eCCPM...



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05-21-2004 Over year old.
 
 
Blackrockminer
Heliman
Location: Somewhere else

LOL!!!!!!!!!

Galifrey

I was just jerking your chain when I said you needed to have your 9Z radio checked. Looks like someone believed you were trying to fly junk. But then poor ole KC is flying wore out servos causing all kinds of interaction. Back when Dinosaurs walked the earth I used to be some sort of mechanic even I was smart enough to know if a socket slipped on all the bolt heads it was probably worn out. Then there is someone who says that there would be no interaction if you flew FM instead of PCM (1024 checks for signal per second). I guess since electricity is 60 cycles per second he flips on a light switch and walks into a room and waits on the bulb to come on. LOL!!!!!!!!!!!

Seriously, since I have become adept at crashing both mCCPM and eCCPM I think that both work well and both need to be setup correctly in order to fly smooth. I do have a question. Are the squash AFR values for Pitch, Aileron, and Elevator the same numerical value..could be where the interaction is coming into play.
05-22-2004 Over year old.
 
 
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