Coaxial Helicopter Support

[MaEtUgR]

Solved Problem

When working on a coaxial fixed collective pitch helicopter project I added back support in control allocation.

Solution

• Add control allocation airframe (CA_AIRFRAME) 12 for coaxial helicopters.
• Allow configuring 2 swash plate servos which is not enough for a normal helicopter with collective pitch but necessary to support the fixed collective pitch coaxial helicopters.
• Adjust a copy of the helicopter allocation for the coaxial use case. These are separate commits to simplify the review of the history.
• Refactor some spacing in the original helicopter allocation.

Changelog Entry

For release notes:

Feature: Add back support for coaxial helicopters with the new actuator allocation
Documentation: Need to add at least a paragraph to https://docs.px4.io/main/en/frames_helicopter/

Alternatives

We could also ...

Test coverage

This was successfully tested on two coaxial helicopter prototypes with fixed collective pitch propellers and two swash plate servos. There was no obvious issue with the allocation found.

Context

Coaxial helicopters were supported previously by PX4 with the old mixing system. I have never flown such a vehicle with the previous implementation but added back support.

FYI @ryanjAA

[hamishwillee]

Documentation: Need to add at least a paragraph to https://docs.px4.io/main/en/frames_helicopter/

You're my hero. It would be good to include a screenshot of the actuator setup, a build log. I'm not sure how much variation between coaxial helicopters is allowed but if there is some flexibility it would be good to state what that is - I mean "if I build a coaxial helicopter how different can it be from your one, and if it can be different by how much and in what ways before this all falls over.

Lastly, what special tuning is needed for helicopters in general, and this one in particular.

[bkueng]

We could move the swash plate into a shared class, but this is fine for now.

px4_fmu-v5_stackcheck is slightly over:

/opt/gcc/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld: region `FLASH_AXIM' overflowed by 589 bytes

[DronecodeBot]

This pull request has been mentioned on Discussion Forum for PX4, Pixhawk, QGroundControl, MAVSDK, MAVLink. There might be relevant details there:

https://discuss.px4.io/t/px4-helicopter-support/34805/3

[DronecodeBot]

This pull request has been mentioned on Discussion Forum for PX4, Pixhawk, QGroundControl, MAVSDK, MAVLink. There might be relevant details there:

https://discuss.px4.io/t/unable-to-locate-airframe-15001-esky-big-lama-v4/31130/6

[bayetan]

I was very happy to see this solution but struggled to implement it in qGroundControl GUI. For others that might be looking as well, you'll have to goto "Parameters" and change "CA_AIRFRAME" to implement this solution.