I don't know why, but IMHO a 140 seems to roll better than a 120. I'd like an answer to this as well
Simon

 

@Piro-flop knows alot about this

 

the 120 deg. swashplate is a geometric standard with all links spaced evenly around the swashplate. A 140 deg. S-plate has the left and right links closer together near the centerline which gives a higher geometric rate between servo and swashplate, which means quicker response to ailieron input and more movement at swashplate per servo movement.

 

140 degree reduces collective interaction from the elevator servo.. with the 120 when you go up and down through the collective range there will be a slight mismatch in elevator motion.

Today , with fast servos and fbl systems, the effect of interaction are barely noticeable. So 120 has become the standard if you like.

But when we had flybars, a lot of the precision machine had 135-140 ccpm. and if your kit had the option of 140 and your radio supported it, you would use 140 all the time to avoid having to use p-mixes to dial out the swash wobble.

 

@Piro-flop ...... So do I stand corrected?

 

@Beaver .......... What your saying i think would also hold true, but the main idea for 140 was to get rid of interaction

 

Great question.
This is my take on it, however i have only owned a Rave 90 eCCPM(140) and a G4 135eCCPM.
120 Degrees - 3 servo
The most common electronic swash mixing type out there, it uses three servos that are equally placed at 120° intervals around the swashplate with the elevator input at the back (most common) of the swashplate, and the aileron & pitch inputs on the left and right sides. The pitch, aileron, and elevator channels are mixed to create the proper CCPM interactions.

The only issue i see is that the mixing/swashplate type is the left and right movement of the swashplate is a fraction faster than the fore and aft movement because of the overall geometry, this is what Piro Flop is referring to as the mis matching. This will cause variations in control as the servos catch up to one another to create the proper swashplate angle.

Ultimately the variation increases at the extreme ends of swashplate travel, never the less, most good flybarless stabilization systems "absorb" these minor speed induced variations.
140 Degrees - 3 servo
To cure the slight speed variation issue that occurs on 120° swash types, RC helicopter manufacturers offer either a 135 degree or 140 degree CCPM. With 140 degree mixing, the swashplate geometry is evened out between the side servos and the front or back servo. This gives more consistent speed interactions between all 3 CCPM servos and reduces small amounts of variation.

I had tried various geometry setting on my G4 which were recommendations from both Marco and Nick Maxwell. I eventually found a geometry setting so good, that i was able to share this with Jack M, who also agreed hi hello felt more direct and precise.
Thunder Tiger seem to focus mainly of the 135 degree geometry format as this is more advantageous on their kit servo lay outs.

Sorry for the rave.

 

@Jeff B & @Piro-flop you dudes know your shiz

 

Piro-flop is right. FBL gyro and fast servos make us lazy. We do not have to bother anymore if swash is 120 or 140 deg.

I setup roll rate in Kbar and that is it. I still keep two 600 FB heads in my drawer. In general FBL is awesome and if I go back to FB it is only for curiosity and play&fun. FBL is mature and way to go.