VTOL Quad Tailsitter Airframe & setup

I’m building a VTOL Quad Tailsitter. It seems like there used to be a SYS_AUTOSTART = 13003 that would be used for Quad Tailsitters. That option doesn’t seem to exist anymore (PX4 1.14.0).

I found on the page Tailsitter VTOL | PX4 Guide (main), which discusses Quad Tailsitters that “Quad tailsitters are easier to fly in hover mode, and more stable in windy conditions. Both are supported using the same aiframe type in PX4.”

How should we setup for a VTOL Quad Tailsitter in PX4 1.14.0? Would be like the following?

  1. Under Airframes: select the “Generic VTOL Tailsitter” Airframe (SYS_AUTOSTART = 13200)
  2. Under Actuators: select “4” from the MC Motors drop down menu
  3. Under Actuators: input the X & Y offsets of the 4 motors
  4. Under Actuators: make sure motors 1 & 2 do have “CCW” selected but motors 3 & 4 do not have “CCW” selected

Yes, that seems to be correct
Then if you have control surfaces just add them in the same window. In case you don’t have any of them and rely just on differential thrust to control attitude, make sure to set CA_SV_CS_COUNT = 0 and VT_FW_DIFTHR_EN depending on your needs ( probably it will be set to 7 which is for the case you control all three angles with diff thrust)

Thank you for checking over my proposed settings.
I am planning on adding elevons (no rudders), but perhaps I should just lock the elevons in place for the first couple test flights.

I’ll post an update on what I find worked best.

Test flight with the aforementioned parameters worked great! I had been trying to hover a quad motor Tailsitter with the 4 motors inline, but didn’t have enough control authority in Pitch with just the elevons. By offsetting the motors so that two were X+ direction and two were in the X- direction (as opposed to all inline) and then using the new parameters resulted in proper flight and hovering in “tailsitter” mode. Next we will work on transitioning to fixed wing flight mode.

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Hello @RaMansell

Could you please send some videos of your flight? did you manage to do the transition? are you using an airspeed sensor?

We have not attempted transition yet. We are currently working on dialing in the PID for hovering in multi-copter mode. Pitch and Yaw were easy, but Roll was the most off–probably because of having the four motors strung out along the wing like it is.

No airspeed sensor yet. It will be installed before we start attempting transitioning to fixed wing mode.

if you need help i can have experience with 2 meter copter tailsitter