Just to be different, I've discarded my "tilting" aileron servo on my
gas Xcell and I am using 2
servos to directly drive the bell-cranks either side of the frames. I am
using the 2 free mixers on my
8UHF to produce the desired pitch/aileron mixing (hence my earlier
However I have noticed undesirable coupling between the aileron and
pitch operation. Its like this:
1) I set it up so that at 0 pitch, washouts arms are horizontal, bell
cranks are horizontal and servo arms are
90 degrees to push rods.
2) At 0 pitch aileron causes servo arms to move in opposite direction
tiltiing the swash plate as required
3) As I change pitch, both servo arms move in the same direction (i.e.
opposite rotation) and the
swash plate moves up and down whilst remaining horizontal.
The problem is when I'm at non-zero pitch and I use aileron. At zero
pitch, each servo arm moves an
equal angle causing the push rods to move an equal and opposite distance
swash plate to tilt without any net pitch movement.
But at no zero pitch, the servo arms are already off-centre. Thus any
aileron input causes one arm to
move towards the centre of rotation and the other to move away from the
centre of rotation. Now
this no longer corresponds to equal and opposite linear movement of the
push rods ( the one
moving towards the centre position travels further). This causes the
aileron stick input to be
coupled slightly (very small) to pitch. I can reduce this effect by
using longer servo arms and using
lower ATV's, but it doesn't seem possible to completely remove this
Question? It would seem to me that this problem is inherent in
electronic CCPM systems, whether
120 or 90 degree. Is this the case?? Do CCPM equipt radios use a
"arcsine()" function to
translate linear rotaional movement to linear pushrod movement (which
would fix this problem)
Or, is it just nto a big enough problem to worry about?