Motion-Capture Experimental Instructions¶
All of the flight-tests or experiments on this page are run using a motion-capture system. In specific, the descriptions are for a VICON system. It is also assumed that the setup instructions from AREAL Hardware Standup Guide have been followed.
VICON-ROS 2-PX4 Setup¶
The following sections detail how to get VICON motion-capture positon feedback onboard the Pixhawk PX4 FMU. This position feedback is routed into EKF2 in PX4, and could be used for either manual position-control flight or autonomous offboard control.
The approach presented on this page and in the AREAL Hardware Standup Guide is generally based on the PX4 Motion Capture Documentation, however some additional modifications of PX4 parameters were required, and ROS 2 was used.
VICON UDP Broadcast¶
The particular VICON settings used are as follows (all in the UDP Object Stream section):
Box next to “Enabled:” is checked
Data Block Size: 256
Box next to “Object per port:” is not checked
IP Address: 192.168.10.2
Port: 51001
ROS 2 VICON Pub-Sub Node Launch¶
In order to start broadcasting the motion-capture over ROS 2, a launch file in the areal_landing_px4_communication package will be used. Make sure ros2-vicon-receiver, areal_landing_px4_communication, and px4_msgs are in a workspace together. Also make sure the subscriber name in px4_vicon_pubsub.py has been changed to whatever ros2-vicon-receiver is publishing. This can be checked by just running the ROS 2 reciever as a test. Finally, make sure the computer-side workspace has been built.
Next, a launch file will start both the ROS 2 reciever node and the pub-sub node that formats the VICON data into the proper message for PX4. Use the command:
ros2 launch areal_landing_px4_communication areal_landing_vicon.launch.py
Note
(5/8/2023) The members of our lab who have been flight testing more recently are out of town for a few weeks to start off the summer. The method they used to launch the VICON nodes is not totally clear, so a launch file was put together for this documentation guide. This launch file has not been thoroughly tested, but it should give a close indication of the proper syntax. This note will be updated as soon as the VICON launch file has been tested.
At this point, motion-capture position and orientation data should be broadcast on the ROS 2 topic vehicle_visual_odometry.
ROS 2-PX4 Bridge Startup¶
A good test to run at this juncture to make sure the system is working is to ssh onto the UAV-based RPi and list the ROS 2 topics. The same vehicle_visual_odometry topic should be visible, and show some data when echoed.
In order to start the ROS 2-PX4 bridge, first some commands will be run through the PX4 terminal in QGroundControl (over telemetry radio link). The instance of the microdds client that runs on PX4 on startup uses a serial connection by default, but we have a connection over ethernet. Therefore, the first command to run in the PX4 terminal is:
microdds_client stop
Then run the following in the PX4 terminal:
microdds_client start -t udp -h <IP of RPi set in earlier step>
Finally, open up an ssh connection to the RPi and run:
ros2 run micro_ros_agent micro_ros_agent udp4 --port 8888
A list of all of the publishers and subscribers for the ROS 2-PX4 bridge should print out, meaning the bridge is active.
This is a good junture to run any final tests desired to check system operation. For example, the UAV can be moved around the motion-capture arena while a topic giving the UAV pose estimation from EKF2 is printed. The UAV local position should match that given by the motion-capture.
