Simulink change PX4 flight mode via MAVROS

I am trying to change the flight mode of a PX4 drone via MAVROS in Simulink. When I send the command ,MAVROS gives me the error:

However, when I run the equivalent code in MATLAB it works. Is it something encoding related?

My model creates the flight mode string, casts it to a ASCII array which has a length of 128. I then convert from 2-D to 1-D and assign the mode to the bus.

[Ankur Bose]

Can you attach the MATLAB code that works for you? We can compare that with Simulink model and see what is the issue

[Ewan Pugh]

Hi Ankur,

This is the MATLAB code:

client = rossvcclient("/mavros/set_mode","DataFormat","struct");
req = rosmessage(client);
req.CustomMode = 'AUTO.TAKEOFF';
resp = call(client, req)

I managed to get the simulink working for this one case by setting the Maximum length of the CustomMode variable length array to 12 (the same as the number of characters in "AUTO.TAKEOFF") and it works. But I now cannot set different flight modes that aren't 12 characters long.

Answer 1

[Abhijeet Gadkari]

Hello Ewan,

You can use the String Length block to output the length of the String Constant and set that value into the CurrentLength field of the mavros_msgs/SetModeRequest message.

This will allow changing the value of String Constant, state, and the CurrentLength field will update with the new value.

You can use the default limits for CustomMode field.

See the example below:

-Abhijeet