CCPM- 120 or 140 degrees for Vbar

Hi All,

Now i thought that 140 degrees was the thing to have over 120 degrees for reduced swash interactions etc.

So now i finally have a heli (Rave ENV) and transmitter (DSX11) that support 140 degree ccpm i was all ready to dive in and use it.

Now i read generally that FBL systems are designed around 120 degree CCPM setups, and the change to 140 degrees on the FBL airframe is not an 'upgrade' as such.

Is this correct that FBL systems (Specifically the Vbar V5 Pro) is 'better' on 120 than 140?

Thanks

Matt

Hi.

In general, 120° proves to be the better concept. With 140° we have not seen a setup that was free of interaction ... it's all about geometry.
Sometimes it seems 135/140° is only a marketing thing to have something else than the others ...

So, 120° is most common, and FBLs are made to go with that. Some, like VBar, allow for any configuration, it's just a matter of rule of proportion to calculate the distances and of entering the angles of the three control links in Pro software, and you're ready to go.

BTW, many 140° setups use pivot arms with a ratio, which is OK for FB heads where this is compensated by the levers within the head, but which is bad for FBL where the geometry has to be different so the servos can make full use of their speed and force and resolution.

Cheers

Eddi

Born to fly ...
forced to work.

Perfect thanks, i will setup for 120

Thanks

Matt

I read something ('fraid I couldn't say where) that suggested a 140 set-up was to compensate for servos being slower than was desirable. It went like this:

With 120, the elevator servo input is twice the distance forward/backward from the mainshaft that the other two servos are. Hence, it has to move ~twice as far in response to an elevator input (that rocks the swash forward/backward).

The suggestion is that if the elevator input is extreme enough, the elevator servo won't be able to move at twice the speed of the other two; so there is a momentary collective interaction. A 140 set-up reducs this. It was then suggested that this wasn't likely to be a problem with modern, fast servos. Hence 120 is fine.