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2_3_Simulation_PX4_Gazebo.md

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Run Px4-gazebo-ROS simulation

Simulation is to test our methods to robots in a safe way and help debug before real-time experiments.

Here, we use PX4-Gazebo to test auto flights. PX4 provides an Offboard mode for auto flights that allow onboard computers to take control of drones.

1. Auto flights with GPS

This is to create a simulation case where drone navigation information is from GPS and IMU.

1.1 Step 1 Config PX4 to use GPS information and offboard mode

First read prearm,arm and disarm specified by PX4. How can I comment on this: it is not better than shit.

Arming and disarming decides what cases will stop drones. One of the cases is that should a drone be stopped, or disarmed, if it cannot receive RC signals for a certain amount of time.

  1. allow arming drones without RC signal We allow drones armed in offboard modes by setting COM_RCL_EXCEPT=4 like

Explanation of COM_RCL_EXCEPT Only setting this can we keep our drone armed when there is no RC input.
  1. change timeout parameters Other parameters can be set to allow more time to take actions
COM_OF_LOSS_T = 10
COM_DISARM_LAND =10 
COM_DISARM_LAND = -1 means disable this

1.2 Step 2 Choose drone controller library

There are several libraries developed for PX4 drones.

Here are some good reps:

1.3 Step 3 Prepare simulation

  1. start by creating a px4-drone model in simulation in Gazebo
roslaunch px4 posix_sitl.launch
  1. call mavros to enable communication between PX4 and PC throught ROS
roslaunch mavros px4.launch fcu_url:="udp://:[email protected]:14557"
  1. apply controller, for instance geometric_controller, to control drone fly
roslaunch geometric_controller sitl_trajectory_track_circle.launch

Note: check if controllers to be run already call mavros or not.

2 Auto flights with Vicon

This simulation case is to simulate drone navigation information is from external vision system, like Vicon and Qualisys.

Let us take Vicon for example.

2.1 Step 1. Config PX4 to use Vicon information

Therefore, we need to configure PX4 such that it takes navigation information from Vicon instead of GPS or IMU. Tutorials are given by PX4, i.e.EKF2 Tuning/Configuration, Using Vision or Motion Capture Systems for Position Estimation

  1. setting EKF2_AID_MASK = 3: vision position fusion + 4: vision yaw fusion, we set position information is from Vicon.
  1. setting EKF2_HGT_MODE = 3: Vision, we set height information is also from Vicon

2.2 Step 2. Create a fake Vicon and feed Vicon information to Mavros

If you dont want to read details, I have provided packages for you drone_simulation_tools.

What you need to do is

  1. clone the packages into catkin_src 
      git clone [email protected]:EEEManchester/drone_simulation_tools.git
  2. build the packages 
    catkin build
  3. run launch file 
    roslaunch drone_simulation_tools drone_sim_vision_map_mavros.launch

Finally, two nodes apart from PX4 and Mavros will be running:

  • package fake_qualisys fakes a Vicon sytem taking drone pose information from Gazebo and publishes to topics in a Vicon way
  • package mocap_to_mavros_sim takes drone pose information from Vicon (through a topic) and publish to /mavros/vision_pose/pose feeding Vicon information to drone.