Odroid and Motion Capture Commmunication

Author: Leonardo Georgescu
Email: georgl3@unlv.nevada.edu
Date: Last Edited 11/08/2018
Keywords: Pixhawk, Drone, Positioning, Mocap, Mocap Calibration, Motion Capture, Autonomous, Automation, Binding, Spektrum,

Motion Capture is one of the best methods for capturing precision 6Dof positioning from a drone. This tutorial covers how to transfer the data from the Motion Capture computer to the Odroid “on-board” computer.

The setup was built by Blake Hament and he taught me how to use the system.

The first step involves setting up the Motion Capture.
1) Turn on the Motion Capture computer and open Motive.
2) To start the motion capture calibration process, click “start wanding.” If a message shows up regarding extraneous markers, click “block markers” before you bring in the wand into the Mocap Area.

3)After about 500 data points have been gathered for each camera, click “calibrate” to start the calibration process. After the calibration is complete, click “apply result.”

If the results of the calibration look good to you, then click “apply.” The best calibration result is usually “great” or above.

4) The Ground Plane is set using a ground plane marker. It's important to place the z axis facing true north. After press “set ground plane.

5) Place the drone 90 degrees from the z-axis which would be either east or west. Assuming that the Mocap markers are already on the drone, select the three points and then right click, select “rigid body” and “create from selected markers.”

6) Then right click, select properties, and change the name to “uav1.”

7) Connect the computer via ethernet cable to the router. On the Motive software, click streaming, view, data stream, and ensure that the data matches the image below.



Now, you have to set the odroid computer to receive data from the Mocap computer.
1) Turn on the terminal on the odroid computer. Make sure to have 4 terminals open.
2) One of the terminals will be used to connect to the wifi. First, ensure that the Odroid is connected to “DASL Warehouse2.” In the terminal, type out “cd catkin_ws/” followed by “source devel/setup.bash”

Then type out “roslaunch vrpn_client_ros sample.launch server:=192.168.50.229” and the following will show up. The IP address at the end has to be the address of the Mocap computer. To find that out, type “ipconfig” in the Mocap computer's terminal.

The image above shows the position of the markers on the drone. 3) If the connection is successful, the terminal should look as the one below. In the image there are two termainals. The bottom one is testing the connection by “ping” followed by the ip address.

4) Another way to test the communication is to use another terminal to search up rostopic and see if the vrpn_client shows up. Whenever accessing any ros function, ensure that you are in the catkin folder

5) The next tutorial will cover accessing Pixhawk data, as well as having the pixhawk flight controller read the position from the Mocap.
For further questions, email me at georgl3@unlv.nevada.edu.