the point of 140deg CCPM?

[Ade_Law]

hi guys,

either im missing something or this whole 140deg ccpm is a bit of a sham.

the main problem with 120deg is that the fore/aft distance of the centre ball on the swash is longer than the mainshaft to the other 2 balls.

this means that when you move the elevator the centre servo has to move further so takes longer to get to its position than the other 2. so when you move the elevator quickly you get a wobble interaction on the collective.

140deg fixes this but now the load is uneven accross the servos. the centre servo takes more load than the other 2. All servos slow down to some extent when they are under load so potentially the centre servo slowing down more than the other two in flight depending on load that is on them.

the nice thing with 120 is that with devices like the cyclock you can slow down left/right servos so that you dont have the wobble on the collective. where as with 140 the slow down is dependant on load so there really is no way to account for it.

what do you think?

Ade

[steelie600]

im hearing what yer sayin ade, but ive been doing loads of research on this cos of me new vibe. Basically it "has the potential" to be a more accurate way of controlling the swash, and yes it probably would load up the front servo more but if yer using really strong servos (mine are 12kg/cm) i cant see it being a problem except in wear to the gears, which is a serviceable item anyway. Now like i said my vibe will run both 120 and 140 ccpm so ill do a little laymans test to see if there is any difference in how it behaves and Ade your more than welcome to participate in this expeiment. I too am interested but im swaying to 140 for accuracy as i need all the hep i can get at the minute

[moyesboy]

I'm with you aide.
with modern fast servos the problem doesn't really exist.

If when you punch the collective the load is not equally shared between the servos and you get a tipping of thre swash then that is easily seen. With 140 degree swash the roll servos will have an easier time and get there first, so you are likely to see some elevator interaction.

It also applies when you stop at the bottom of a vertical descent when the more heavily loaded back servo will have a harder time holding centre.

When you are operating the elevator and the heli is tumbling, are you really going to be able to detect a slight collective interaction, that is there only as you increase or decrease the elevator? I think not as in most manoevres with tumbling you are also moving the collective too.

With BLS451 or JR8717 you are probably best on 120 degrees I reckon.

<edit>
the swash loads are there all the time, and with 120 degrees they are shared equally between the servos most of the time. So the servos will all push off the desired position equally when you pull G or whatever. With 140 degree the loads are not equal any of the time, so the servos will push off target position by different amounts all the time. so the centring error interaction will be worse all the time just so you can be more accurate during the times you are actually moving the elevator (when I reckon you will hardly notice any collective error anyway).

But can you really setup the bike lock to take account for the speed diffenence with the elevator on 120 degrees ccpm? That speed difference will be totally different when the heli is flying compared to on the bench...

[Ashley Davis]

it depends on whether the servo actually does slow down I guess and by how much.

[Steve]

What you need is 4 point 90 deg CCPM.

[robgt]

My Vibe 90 flew better on 140° CCPM than on 120° CCPM - and 120° was already very good.


The cyclics felt sharper, and it flew very very accurately on 140°.
Cheers,
Rob

[Leebert]

Interesting thread...
I've not noticed any issues with any 120 CCPM heli and I've not flown the Vibe enough to notice any issues with that.
However, setting up the Vibe on the bench (with a DX7), I couldn't quite get the swash to move up and down level. There was always a slight error at the extremes of pitch. I spent a lot of time fiddling with the amount of mix but I couldn't quite eradicate it.
Is it worth converting it to 120 CCPM or are there problems going that way too?

[steelie600]

just gonna suggest that steve. 4 servos, all on one swash operating EXACTLY equally perfect me thinks

[Nicolasgreening]

I am a complete novice and this is a little off topic but I have always wanted to know what was wrong with the raptor setup?

There must be a fundamental problem as most new helis are either 120 or 140 CCPM...
But the swash had 90 inputs and the collective was separate so did not interact with the swash at all?

Thanks

Nick

[steelie600]

Basically its down to having only one servo operating collective and to do hardcore 3d stuff you need one hell of a servo to keep up (speed and powerwise). with 3 servos operating collective you can in theory use less powerful servos and youll see a faster acting swash

[Nicolasgreening]

Kev,

Cool thanks makes a lot of sense...

Nick

[jboweruk]

:lurk5: Just lurkin', as I don't know any of this stuff, could somebody just explain how 140 works please? And surely wouldn't 360 be the best? As someone pointed out, 1 servo each front and rear plus 1 each side? Wouldn't that be 360?

[robgt]

120 is called 120 because there are three connections to the swashplate separated by 120 degrees.

140 was devised by Curtis Youngblood to reduce interaction common to the 120 ccpm system. He called it 140 because it sounded better than what it actually is, which is two lots of 135 (ish) and whatever the remainder is between the front two to complete the 360 (which may or may not be around 90 degrees)

http://www.curtisyoungblood.com/faqs/search.php?id=948

All of them end up at 360 because they all surround the swashplate - 90 is called that because of the angle between any two balls on the swash (4 balls at 90 degrees apart).

I hope that helps
Cheers,
Rob

[mchristyuk]

Jboweruk,

You have two types of control setup on a helicopter. Either eCCPM or mCCPM. (Cyclic Collective Pitch Mixing).

With eCCPM the mixing occurs in the transmitter and with mCCPM (Raptor) the mixing occurs on the model.

With eCCPM comes a number.

The number refers to the angular displacement between the servos. Therefore 360 would acutally be 90.. 90 degrees between each servo.

As Ade said 120 has the problem in that 2 servos sit much closer to the main shaft than the third meaning that 1 servo has to travel further than the rest.

140 was thought up by Curtis and implemented on the Vigor before such devices as the Cylock existed.

It is mechanically better as the 3 servos are now equidistant from the mainshaft. Yes the loading will have a small impact but I think it is neglible and from flight tests by World Champion pilots 140 proved to be better in the air as well as on the bench.

I am one who believes in keeping things simple.. the less there is the less there is to go wrong.. therefore I don't run regulators and I don't run any kind of eCCPM mixing device. For this standard setup 140 is optimal in terms of eCCPM.

With 90 you have 4 servos and therefore equidistances and equal loading.. but you now have 4 servos to match instead of 3 and you really are going to have to have a lot of patience or use a cylock for the best setup. You also have more current draw.

The most mechanically pure setup is mCCPM.. and for F3C style of flying I still believe it is the best. However with hard pitch pumping 3D you want as many servos as possible working for you so eCCPM is the way forwards..

Cheers

Mark

P.s. What Rob said

[moyesboy]

No system uses 4 servos on the swash at 90 degrees.
90 degree eccpm uses just three servos with just one doing the elevator (or airleron) and two doing the aileron (or elevator).
IF you had 4 seevos on the swash then slight errors in the angular outputs on the servos would make the serevos fight eachother and try and bend the swash. With three servos each can feely move to position without them all having to agree exactly.
Its interesting that flying tests seem to show the 140 degree as superior. I'm thinking that this must be quite servo dependant and results may be different with faster low torque servos compared to slower high torque servos. I'm thinking that F3C setups are probably using very high torque but lower speed servos for accuracy and then finding 140 degrees is best.
for 140 degrees to fly better than 120 I think the servos must hold their desired position very well, but have a noticable speed lag.

To throw something else in, with 140 degree the servos will move different amounts with airleron than they will with elevator. So the speed of response to aileron and elevator will be different.
with 120 then the cyclic response is in theory equalised around the circle. So maybe chaos manoevres should be superior with 120 degree even if there is some collective error.