2 servo CCPM

[pgkevet]

..why not?

[pchristy]

Because you need to locate the swashplate in 3 dimensions, which implies 3 location points.

Actually, you can do it, but only with fixed pitch! (Swashplate limited to two axes)

[tourerjim]

How would collective work?

[electricsceadu]

my old graupner star ranger is running 2 servo eccpm
and its a very poor system and its collective pitch, it has that many interactions that you can't dial all of them out
you need to be on the ball to fly it
i've never got around to converting it to 3 servo eccpm
but maybe oneday i'll do it

[joe.lel]

How would you keep it level with only 2 points of contact???

[pgkevet]

How would you keep it level with only 2 points of contact???

I see no reason why you can't use servos at 90 degs to each other..even on a pushpull across the swash. If you think about it then 3-servo ccpm still needs the elevator and or aileron servo to move up/down with pitch..2 servos can do the same thing.

Since we now have higher res servos and rx's and stroner servos it ought to be possible. An argument for interaction..well with 2 servos there may even be less interaction than getting three to work together. It's the radios that do the computation that screw up as much as the servos?

[trillian]

What would be most logical is 4 servo eCCPM. With three servos inevitably the elevator servo has to work harder because although the swash is supported equally for collective it still tilts in (mainly) two directions for cyclic.

[pgkevet]

4-servo exists..recommended on the vario acrobat for example. But as I postulated little difference between that and a push-pull 2 servo ssytem (as in push one side swash, pull the other)

[electricsceadu]

on the 2 servo eccpm there is a third servo that is mechanicaly mixed onto the swash
the two servo's work together as in 3 and 4 servo eccpm
the third servo works on its own
its a very long time ago i set the model up and i'd need to take the top off the model to see how it is all linked together
from what i remember it is a real pig to get your head around how it works the first time you look at it
looking at my tx
the futaba swash type is swh2
and aileron and pitch is mixed in the eccpm

[pchristy]

I see no reason why you can't use servos at 90 degs to each other..

So how will it tell the difference between (say) full left and full back at the same time, from full collective? (Assuming left and back are both "push" commands)

[pgkevet]

So how will it tell the difference between (say) full left and full back at the same time, from full collective? (Assuming left and back are both "push" commands)

It's the tx that works it out and send the data from the three 'channels' of the tx to the two channels of the servos.

As it is with 3 servo ccpm you angle the swash with a balanced mix of up front and down back for up elevator action and whole swash up/down for pitch..just do the same. The only difference is you only use 2 servos

[davie]

how would a 2 servo push pull system work pitch if the servos have to push to move the swash up then what does the pull do ?? i cant see how this would work unless the pitch was controlled by a separate servo then its not eccpm more like the raptor system ?

[pchristy]

I look forward to your demonstration of this mechanical masterpiece!

[Mark_T]

I don't see how you can position and hold the swashplate with 3 degrees of freedom using only 2 control points.

At some point you'll find yourself trying to hold position in two directions while needing to drop or lift in the third which you can't do with just two servos even if you manage to get some sort of push-pull arrangement going.

[SRH990]

What would be most logical is 4 servo eCCPM. With three servos inevitably the elevator servo has to work harder because although the swash is supported equally for collective it still tilts in (mainly) two directions for cyclic.

This is the reasoning behind 135 or 140 degree swash plates, all the servo to swash connections are the same distance from the mainshaft, this way if you give forward elevator, all the servos have to move the same distance so as long as the servos are all the same, they will complete the move at the same time so no lagging servos.

I'd say this is probably my ideal as all the servos are doing so much work in CCPM setups, the fact they are 'elevator' or 'aileron' is immaterial. With the fast, high torque servos we use now there is actually very little to be gained using this in preference to 120 degree CCPM.