How to use MAV_CMD_DO_SET_ACTUATOR in MATLAB?

[Xiaowei Xing]

Settings

Pixhawk 4
PX4 1.14.0
MATLAB R2023b

Question

I want to send rotor commands to Pixhawk from MATLAB through telemetry radio. After some search, I think MAV_CMD_DO_SET_ACTUATOR is the appropriate interface. I can arm Pixhawk from MATLAB using MAV_CMD_COMPONENT_ARM_DISARM. However, I cannot make MAV_CMD_DO_SET_ACTUATOR work. My code is as follows.

tele_com_port = "COM16";
device = serial(tele_com_port, "BaudRate", 57600);

dialect = mavlinkdialect("common.xml");
mavlink = mavlinkio(dialect);

% Arm, MAV_CMD_COMPONENT_ARM_DISARM 
cmd_arm = createcmd(dialect, "long", 400);
cmd_arm.Payload.target_system = uint8(1);
cmd_arm.Payload.param1 = single(1);
buffer_cmd_arm = serializemsg(mavlink, cmd_arm);

% Set rotor input, MAV_CMD_DO_SET_ACTUATOR
cmd_set_actuator = createcmd(dialect, "long", 187);
cmd_set_actuator.Payload.target_system = uint8(1);
cmd_set_actuator.Payload.param1 = single(0.1);
cmd_set_actuator.Payload.param2 = single(0,1);
cmd_set_actuator.Payload.param3 = single(0,1);
cmd_set_actuator.Payload.param4 = single(0.1);
buffer_cmd_set_actuator = serializemsg(mavlink, cmd_set_actuator);

fclose(device);
fopen(device);

% Arm.
fwrite(device, buffer_cmd_arm, "uint8");
fprintf("Armed\n");
% Set rotor inputs.
for i = 0: 1000
    thr = (0.8 - 0.2) / 1000 * i + 0.2; 
    cmd_set_actuator.Payload.param1 = single(thr);
    cmd_set_actuator.Payload.param2 = single(thr);
    cmd_set_actuator.Payload.param3 = single(thr);
    cmd_set_actuator.Payload.param4 = single(thr);
    buffer_cmd_set_actuator = serializemsg(mavlink, cmd_set_actuator);
    % fwrite(device, buffer_cmd_set_actuator, "uint8");
    fwrite(device, buffer_cmd_set_actuator);
    pause(0.02);
end
fprintf("Done\n");
fclose(device);

I checked the document at https://github.com/PX4/PX4-user_guide/blob/main/en/payloads/README.md#generic-actuator-control. However, there is no Peripheral via Actuator Set in my QGC. The current settings about the rotors are as follows.

Thanks in advance.

[Hamish Willee]

Unfortunately this feature is not present in 1.14 - see PX4/PX4-Autopilot#21966

It is still in the docs because it should not have been removed and I have been trying to get it added back.

[Beat Küng]

@Everglow0214 Offboard Actuator Set is correct, it got renamed to Peripheral via Actuator Set after 1.14.
You have to set COM_PREARM_MODE to Always, if you want to use it while disarmed.
And it is working on 1.14 as well.

[Xiaowei Xing]

@Everglow0214 Offboard Actuator Set is correct, it got renamed to Peripheral via Actuator Set after 1.14. You have to set COM_PREARM_MODE to Always, if you want to use it while disarmed. And it is working on 1.14 as well.

Thanks for your reply.

I can arm Pixhawk now. In the code above, I set the rotor inputs to increase linearly. But the rotors' speed seem does not change. And Pixhawk disarms even when the program above is still running.

I guess I have to try a lower version of PX4.

[Hamish Willee]

Thanks @bkueng - the docs look correct then thanks.
I didn't know you could/should use do set actuator to control motors for external input

@Everglow0214 Beat is saying that this should work on main and v1.14 so trying a lower version probably isn't necesssary - something else is going on.

The vehicle is probably disarming because it isn't getting the ARM command - and in normal use it will turn off so the rotors don't spin on the ground too long. You might need to disable this - see https://docs.px4.io/main/en/advanced_config/parameter_reference.html#COM_DISARM_PRFLT

If that doesn't help, please repost the query on the discussion boards - this is no longer a "docs issue".

[Dronecode Bot]

This issue has been mentioned on Discussion Forum for PX4, Pixhawk, QGroundControl, MAVSDK, MAVLink. There might be relevant details there:

https://discuss.px4.io/t/how-to-use-mav-cmd-do-set-actuator-in-matlab/36651/1