Adding 4th motor in Tri-Copter configuration

Hey all,

This is my first post here, I have used Ardupilot and pix-hawk 4 in both fixed wing, multi-copter configurations and I have built up a Nimbus VTOL in the past. So not a total noob but my knowledge is limited in a way that I never had to make changes to the existing firmware (until now) so please go easy on me. Also, I have a friend who is helping me out, he has some embedded firmware experience but not anywhere close to building a flight controller.

I am trying to build an F-35B model plane inspired by a few youtube creators. My progress so far has been

  1. Built a custom 3 Bearing Swivel Module(BSM) hardware and software using STM32 microcontroller
  2. Built a frame to support 4 EDFs - 1 with 3BSM, 1 at the front and 2 on the wings for roll.
  3. Currently, working on the electronics of the model with Pixhawk 4 and sooner than later, I will have to get my hands dirty with the firmware, Ardupilot (which I am excited to get going). I will need the help of the community to accomplish this step of the process.

Things I know about Ardupilot firmware on the Pixhawk controller for such a project:

Based on the openly available information on the internet, I think I will have to start with a Tri-copter class and add a 4th motor to the front, essentially making my setup a plus configuration quad with the yaw servo (unlike differential yaw movement in traditional quads).

In forward flight, just the rear nozzle tilts forward as if it were simply a motor tilt servo. From what I can tell, the stock tiltrotor implementation in Arduplane can almost handle this configuration, but needs one tweak. In hover, yaw needs to be mapped to a tricopter-style tilt servo (my swivel nozzle accepts a PWM input for yaw vectoring) rather than the typical differential torque setup of the quad frame type.

Can anyone point me in the right direction to add this behavior? I can try to wrap my head around the massive code base but don’t have enough experience with Ardupilot to make meaningful edits without some guidance from the community.


Please note that I changed the topic to VTOL as it is the final configuration

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