Cyclic Swashplate support for Coax Copter

[bnsgeyer]

There have been several users attempting to use Ardupilot to control coaxial helicopters that have fixed collective pitch rotors but have cyclic swashplate control. The tradheli code does not handle fixed collective pitch, variable speed main rotors. The multirotor Coax copter frame is better suited for this helicopter type but it cannot handle the unique swashplate types.

Since @IamPete1 has recently cleaned up the swashplate library to be more self contained, it seems reasonable to use this library in the Coax copter to provide users the ability to control these helis.

Here is a link to a thread where users are requesting support for this special helicopter type https://discuss.ardupilot.org/t/new-co-axial-heli/60067/35 https://discuss.ardupilot.org/t/coaxcopter-coaxial-is-not-working-on-heli-firmware-4-3-7/102270

Is your feature request related to a problem? Please describe. Users trying to setup a coaxial helicopter with fixed collective pitch cannot use Coax copter because it doesn't support swashplates

Describe the solution you'd like Incorporate the swashplate library into coax copter to enable users to use this frame type to control this special helicopter type.

Describe alternatives you've considered This special helicopter type could be made into a frame in the trad heli code but it doesn't seem logical as this helicopter type uses variable speed fixed collective pitch to control the thrust. It would probably be more difficult to implement into trad heli

Platform [ ] All [ ] AntennaTracker [X] Copter [ ] Plane [ ] Rover [ ] Submarine

Additional context Add any other context or screenshots about the feature request here.