VTOL: Separate pusher throttle control during transition

[mart1npetroff]

Current Behavior

In a VTOL setup with a dedicated pusher motor, there does not seem to be a straightforward way to control the pusher throttle separately during transition using a different RC channel or another dynamic input source.

At the moment, the pusher motor can be mixed as an additional motor, but its throttle contribution appears to be static within the mixer. This makes it difficult to shape transition behavior in a flexible way, especially when trying to smoothly increase forward thrust while reducing lift motor authority at the same time.

For example, in my case I would like to control the pusher motor independently during transition, so I can gradually increase pusher thrust while the vertical motors are reduced in a controlled way.

Desired Behavior

It would be very useful to have a way to control the pusher motor throttle separately during VTOL transition.

This could be done through:

• a separate RC channel
• a logic-condition-driven value,
• or another dynamic internal control source.

The main goal is to allow smooth and tunable transition behavior by controlling pusher thrust independently from the main throttle logic when needed.

Suggested Solution

One possible solution would be to allow the throttle weight/value of an additional motor in the motor mixer (for example motor 5 in a VTOL setup) to be driven dynamically via GVAR and logic conditions.

That would make it possible to:

• increase pusher throttle progressively during transition,
• reduce vertical motor influence at the same time,
• and create more flexible transition strategies depending on flight mode, conditions, or user-defined logic.

For example, if the throttle coefficient of the pusher motor could be assigned to a GVAR, then that GVAR could be changed dynamically through logic conditions or mode-based rules.

Of course, the implementation could also be done in a different way if there is a better architectural approach in iNav. The GVAR / logic-condition-based approach just seems like one of the most flexible options from a user perspective.

Who does this impact? Who is this for?

This is mainly useful for advanced VTOL users, especially people using multicopter + pusher hybrid configurations and trying to fine-tune transition behavior.

It would be particularly valuable for custom VTOL platforms where smooth forward transition is important and where the default mixer behavior is too static.

Additional context

The motivation is to achieve a smoother transition by ramping up the pusher motor while reducing the vertical motors in a coordinated way.

Right now, a static mixer does not provide enough flexibility for that use case.

A feature like this could improve transition tuning for custom VTOL aircraft and reduce abrupt behavior during the handoff from vertical lift to forward flight.

[sensei-hacker]

when trying to smoothly increase forward thrust while reducing lift motor authority at the same time.

For example, in my case I would like to control the pusher motor independently during transition, so I can gradually increase pusher thrust while the vertical motors are reduced in a controlled way.

If I'm understanding you right, you would like that actuator to smoothly transition between the two profiles. Rather than a sudden switch.

Would the same concept not apply to all actuators?
There's nothing really special about a pusher motor in particular here, right? We'd like gradual transition from one profile to another?

[mart1npetroff]

Yes, theoretically that is a broader version of what I mean.

When I wrote the request, I intentionally described it in a simpler and more concrete way so the use case would be easier to understand. My immediate use case is the pusher motor, but the underlying idea is indeed a smoother transition behavior rather than a sudden change.

Also, as far as I understand, transition in iNav does not really switch between different PID profiles in a gradual way. It still uses the same PID profile (PID 1), while performing additional transition-related actions defined by the mixer, and possibly logic conditions if configured.

So when you mention a smooth transition between two profiles, that sounds to me like an even better and more complete solution: not only gradually changing actuator weights, but also gradually blending the authority of two different control profiles / PID behaviors during transition.

That would probably be the ideal solution:

• gradual change in actuator weights
• and possibly gradual blending of controller behavior as well

The reason I originally described it through the pusher motor is because that is the most obvious practical pain point in my setup.

To give some context: I tried X-Plane 12 with the Alia 250 eVTOL, where vertical motors and pusher throttle can be controlled separately. That allows a very smooth transition, because one throttle can be reduced progressively while the other is increased at the same time.

So yes, my request is motivated by the pusher use case, but I agree the more general concept may be smooth blending of actuator outputs, and possibly control behavior too, during transition.

[Sibre3]

The 4 + 1 transition from a VTOL to fixedwing flight only occurs in the mc mixer profile. It's when the transition mode is selected that the pusher motor is enabled for forward flight in that profile.
Once transition mode is exited to the fw mixer profile. Throttle stick control over the pusher motor is then given to the pilot.

This explains how ardupilot quadplane also allows the use of throttle stick control over the pusher throttle while the hover motors are active. This is useful if you want to move the quadplane forward while hovering to enhance lift from the wings while still providing some lift from the quad motors. https://ardupilot.org/plane/docs/quadplane-flying.html#manual-forward-throttle-in-vtol-modes