Fixed wing : Acro mode?

[Daannoa]

Hello,

​As a new INAV user, I need some clarification on how the firmware operates, specifically regarding Acro mode.

​I have built a Phoenix 2400 motor glider equipped with a SpeedyBee F405 flight controller. For now, I haven't installed a GPS, as my primary goal is to benefit from "basic" stabilization.

​While I understand how Manual and Angle modes work, I am surprised to see that my ailerons do not move when I tilt the aircraft manually while in Acro mode. Based on my research online, Acro is a stabilized mode. I have read conflicting information: some sources say the model must be armed to see the surfaces move, while others suggest the physical movements must be very sharp/abrupt to trigger a response. Unfortunately, I haven't found a clear answer on how the stabilization logic actually behaves in this mode.

​For context: the model is airworthy, Autotrim and Autotune have been successfully completed, and Angle mode works exactly as expected.

​Could you provide some details or confirmation on how Acro mode functions? Is it possible to see the stabilization effects by tilting the model by hand on the ground, similar to how it works in Angle mode?

​Thank you in advance for your help.

[sensei-hacker]

Acro mode can also be called Rate mode.
Your sticks control the rate of rotation.

If you set the maximum roll rate as 360 degrees per second, then full stick deflection will move the servos enough to roll at 360 degrees per second. Ignoring "expo"-like effects, 10% stick deflection would be about 36 degrees per second.

Stick center would be about 0° per second - try to keep the current attitude. (But only by looking at how quickly it's diverging, in the current implementation).

In theory, the control surfaces move to counteract when you manually spin the plane. But for the control surfaces to react very much, you'd need to spin the plane fast. You can't see a small aileron movement while you're making a big movement with the airplane. Side note - this is actually how most slight of hand works. The magician moves their entire arm or hand in an obvious way, while making a small sneaky movement with one fingertip. You can't see my fingertip move if I'm swinging my whole arm. :) The same idea applies here - you can't easily see a small movement of the aileron while the entire wing is swinging around.

This is especially true when the aircraft is not flying. The response is muted when not flying, because you wouldn't want the control surfaces to be deflected hard as you launch, trying to fight against your arm strength. As soon as you let go, the airplane would dive right into the ground or go straight nose up or something, if it had been trying to fight your arm moving the plane around. (I-term wind-up). So the response is limited until it's flying.

[Daannoa]

Thank you for the explanation. How this mode works is a bit clearer to me now.
So, in short: in Acro mode, stabilization is only active while the glider is in flight.

​Is it possible to adjust the 'aggressiveness' of this stabilization through an iNAV parameter?
Right now, I can't feel any difference in flight between Manual and Acro mode.
I tested it in calm weather (where I didn't expect a difference) and also on a windy day with small gusts, but I didn't notice any difference between the two modes.

[sensei-hacker]

You might look at the PID Tuning category in the wiki - there are several related pages.

Rate mode should feel pretty similar to a well adjusted plane in manual mode, though.

The action of the flight controller is more obvious in Angle and other modes.