Mavros mavcmd 213: unexpected command error with result 0

asked 2021-09-22 09:24:03 -0600

ahalic gravatar image

updated 2021-09-24 01:37:48 -0600


I am trying to use mavcmd 213 from within a Python script. However, I have encountered an unexpected problem. When executing the script, I get the error CMD: Unexpected command 213, result 0.

After reading mavros documentation it seems to me result 0 is equal to the command being valid and being executed, which is even more confusing.

Additionally, when I manually enter the command via rosrun mavros mavcmd long 213 <heading> <speed> <absolute> 0 0 0 0 0 the command is successfully executed.

Moreover, despite the unexpected command error it seems that the command is actually executed (at the moment I have no access to my engine/rotors to check if they are actually moving), because if the command is not resent in a loop i get the FCU: target not received last 3secs, stopping.

Below I attached a snippet of my Python code that executes the command, maybe something is wrong here:

set_yaw_speed = rospy.ServiceProxy('mavros/cmd/command', CommandLong)
syw = set_yaw_speed(broadcast=1, command=213, confirmation=1, param1=self.course, param2=self.speed, param3=0, param4=0, param5=0, param6=0, param7=0)

I left the param3 to 0 intentionally, as its meant to be absolute course. The self.course and self.speed are floats that are attributes of an object, but I tried substituting them manually for a predefined variable, which changed nothing. I can provide bigger part of code if necessary.

I should probably add I am running ROS Lunar with Pixhawk 2.1. I am running Ubuntu ver 16.04 kernel 4.15.0-142-generic.

I would be much obliged for any help or tips or explanations. Thanks in advance. If any additional information is needed I will be glad to try to provide it.

Added full code as requested by osilva.

Some explanation: Desired course and desired speed are floats with 1 decimal precision. They are read from topic /AC_man which is a custom topic to which desired course and speed are published after being calculated by a standalone module written in C#. Mode is also changed by a standalone python script which listens for a string on topic /mode_command and executes mavcmd 176 (I can confirm it works, as Pixhawk mode gets changed).

Full code below:

#!/usr/bin/env python
# - *- coding: utf- 8 - *-
import rospy
from hh_1.msg import ac_man
from std_msgs.msg import Float64
from mavros_msgs.msg import VFR_HUD 
from mavros_msgs.srv import CommandLong
from hh_1.msg import mode_cmd

class AntiCollision():
    HDG_TOPIC = '/mavros/global_position/compass_hdg' #where to listen for current heading
    SPD_TOPIC = '/mavros/vfr_hud' #where to listen for current speed
    AC_TOPIC = '/AC_man' #where to listen for anticollision maneuver
    COURSE_HYST = 2.0 #course hysteresis for maneuver [deg]
    SPEED_HYST = 0.3 #speed hysteresis for maneuver [m/s]
    SERV_TIMEOUT = 10 #service timeout [s]

    def __init__(self):
        self.current_mode = 'AUTO'
        self.current_course = None
        self.current_speed = None
        self.desired_course = None
        self.desired_speed = None
        self.course_type = 0 #0 - absolute course, 1 - relative course

    def AC_callback(self, data):
        """Get vehicle desired (new) course and speed"""
        self.desired_course = float(data ...
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Yes please share more code. I’d like to see how you wait for the message for example. Thank you

osilva gravatar image osilva  ( 2021-09-23 18:17:06 -0600 )edit

Added full code with some explanation.

ahalic gravatar image ahalic  ( 2021-09-24 01:33:36 -0600 )edit