INAV and Mavlink problem

[lioliopoulosk]

Hello guys,

I have developed a sensor system using ESP32 which is connected via UART to my FC and reads Mavlink messages. I can read values like Vbat, RSSI, GPS values etc. but I can't find a way to detect when the drone is on the ground. I think that the FC (INAV) sends some specific Mavlink messages and not the one I am looking for.

Do you know which Mavlink message ID is connected with the flight state of the drone?
Also, is there a way to tell INAV what Mavlink messages to send?

Thank you!

[sensei-hacker]

I'll mention a few things.

First, be aware you're speaking to INAV in a foreign language. INAV speaks some Ardupilot (Mavlink), but you'll have much richer communication in INAV's native language, MSP.

I don't know of a "I'm touching the ground" Mavlink message, and really INAV doesn't know for sure if it's in a tree or not - it can't see trees. Or sitting on a hill.

You can infer whether it's likely to be airborne by considering a few factors:

Has it ever left the home point (the arming position)?
Has the altitude increased more than two meters?
If it never moved from the arming point, and never went up, it's probably still on the ground.

Is it even armed?

Is the throttle significantly above zero? Has it ever been? If the motors never throttled up, it's probably still on the ground. Indeed if the motors have been at zero throttle for the last 60 seconds it may be on the ground (but gliding exists. Blimps also exist).

Is it moving? Either laterally or vertically? Or rotating in pitch, yaw, or roll? If it's dead still, it's probably on the ground. (A tree is part of the ground).

But - it can be in a tree and the wind may be moving the treetop around a bit. (Maybe the fact it's too windy to fly is WHY it got stuck in a tree).

If it WAS flying 1 second ago, maybe it still is.
If it was on the ground 1 second ago, maybe it still is.

One way to express all that is a 100 point scale.
Then something like:

30 points for "it's currently moving vertically".
30 points for "it's currently moving laterally".
-80 points for being disarmed
20 points if altitude has exceeded 3 meters in this arming cycle
20 points for throttle above midpoint
-20 points for for throttle below 10%
5 points for it was flying the last time I checked
-5 points for it wasn't flying 1 second ago

If the combined score is higher than 50, it's probably flying.
Based on your own mission and your own vehicle you can set your own thresholds for "it's flying", "it's not flying" and "unknown".

Some of this is vehicle-specific, of course.
A quadcopter has the motors spinning if it's airborne, or it won't be airborne very much longer. That doesn't apply to a blimp, a glider, a submarine, etc.

Quadcopters don't move very far when they're on the ground. Cars do; boats do.

[lioliopoulosk]

Thank you for your response!

In the recent updates, I have seen that INAV support Mavlink telemetry. My only issue is that I can't find if I can change the stream rate of the messages using CLI.
The system I'm developing is using some environmental sensors and I want it to save data to an SD automatically when the drone is on the ground.
I've been working with mavlink for months and never had a problem with other telemetry values like rssi, sats,vbat,lat,lon,alt and many more.
I know that EXTENDED_SYS_STATE (245) is the Mavlink message that holds the parameter of the landed_state of the drone but I don't know if INAV can send this message. You can check the message list of Mavlink here: https://mavlink.io/en/messages/common.html

[sensei-hacker]

Thanks for the additional info.

I don't see that message implemented in https://github.com/iNavFlight/inav/blob/master/src/main/telemetry/mavlink.c

It looks like it has only two fields, so it would likely be straightforward to add if you want to do a pull request.