Px4-autopilot: Kill switch for companion computer

[cimbar]

Hi,
In 1.8.2 release and before, disarming with mavlink message was possible. I was using mavros and sending mavros/State message as armed=false and it was working as same as manual kill switch. While flying in offboard mode with companion computer and not using RC controller, this was an option for emergency stop. When i passed to 1.10 version, i realized that this option is not possible anymore and returns this error:
FCU: Disarming denied! Not landed
If i am missing some parameter to change, i am sorry but if there isn't any possibility for emergency stop via mavlink message, i think it should be implemented.
Thanks

[TSC21]

You need to send the arm command with the param 2 set to 21196. https://mavlink.io/en/messages/common.html#MAV_CMD_COMPONENT_ARM_DISARM. You can use the mavcmd for that same purpose.

[TSC21]

You can also extend mavsafety with that option, and its actually the best way of doing it. If you do it so, please issue a PR to MAVROS, so everyone can benefit from it.

[cimbar]

Following your suggestion, i used mavros_msgs/CommandLong service on /mavros/cmd/command topic inside of the code instead of using mavcmd. Also, users can call service from bash with

rosservice call /mavros/cmd/command "{broadcast: false, command: 400, confirmation: 0, param1: 0.0, param2: 21196.0, param3: 0.0,
  param4: 0.0, param5: 0.0, param6: 0.0, param7: 0.0}"

Thanks for help

[julianoes]

Alternatively there is also:
https://mavlink.io/en/messages/common.html#MAV_CMD_DO_FLIGHTTERMINATION
But for this the flight termination circuit breaker might need to be disabled.

[TSC21]

Following your suggestion, i used mavros_msgs/CommandLong service on /mavros/cmd/command topic inside of the code instead of using mavcmd. Also, users can call service from bash with

rosservice call /mavros/cmd/command "{broadcast: false, command: 400, confirmation: 0, param1: 0.0, param2: 21196.0, param3: 0.0,
  param4: 0.0, param5: 0.0, param6: 0.0, param7: 0.0}"

Thanks for help

@cimbar are you interested in extending the mavsafety with the feature as well? Like a kill command?

[cimbar]

https://github.com/mavlink/mavros/pull/1405