Starter Code to get a drone flying autonomously

Hardware Setup

• Quadrotor running PX4 on a Pixhawk 2 Cube (Black)
• Jetson Nano connected to drone over UART connection
• Jetson Nano connected to wifi which is also connected to vicon computer
• Vicon Computer running Vicon Bridge 3.1.3 (later versions might work, unclear)

PX4 setup

Mostly pertaining to mocap setup.

1. Basic quad setup: basically just follow the steps one by one from top to bottom on the left

• airframe setup: coose quadrotor x, either generic or DJI F450 (for the bigger quads in our lab) - choosing a specific frame means that the PID values are likely to be better
• sensors: run the sensor calibrations
• radio: calibrate the radio to make sure everything is moving in the direction as you wiggle the radio
• flight modes: the useful ones are
  • manual - which is hard to fly, but kind of raw
  • stabilised - (my prefered mode) - keeps the quad as level as possible, but will tend to drift in position
  • position mode - requires GPS/vicon data so that the quad knows where it is, but will generally hold its position and altitude
  • offboard mode - which expects the offboard computer to send waypoints or velocity commands. these commands must be arriving at atleast 2Hz, but we normally send them at atleast 20Hz.
• safety: set appropriate failsafe settings

2. When creating an object in Vicon Tracker, point the front direction of the quad along the vicons x axis, and create the object. this ensures that the yaw angles are calculated correctly.
3. Within PX4, in QGC
4. Ensure GPS is not required: set COM_ARM_WO_GPS set to allow arming without GPS
5. Enable Telem2 connection:

• MAV_1_CONFIG = TELEM 2 and then reboot
• MAV_1_MODE = ONBOARD
• SER_TEL2_BAUD = 921600

6. Enable MOCAP fusion

• EKF2_AID_MASK check only the fields vision position fusion and vision yaw fusion instead of GPS
• EKF2_HGT_MODE set to vision instead of barometer
• EKF2_EV_DELAY set to 50 ms. Technically, should be measured (follow instructions on px4 guide (https://docs.px4.io/master/en/ros/external_position_estimation.html)
• EKF2_EVA_NOISE set to the minimum value (2.86 degrees in our case), ie you are saying that the vicon data is absolutely true
• EKF2_EVP_NOISE set to the minimum value (0.01 meters in our case), same as above

7. radio control setup

• Set arm switch
• set kill switch
• set flightmode switch verify that the correct things are highlighted as you toggle the switches on the radio

8. failsafe set setup

• set everything to terminate/land as appropriate

Something that troubled us for a while was that the device id of the drone was set to 7, but mavros was publising to device 1, and so they couldnt talk to each other.

Jetson Set up

• Create a catkin workspace: eg.

cd 
mkdir catkin_ws
cd catkin_ws
mkdir src

• Clone this repo into the workspace

git clone <this repo>

• Build the workspace

catkin build

• Everytime you restart the jetson, you need to run

sudo chmod 666 /dev/ttyTHS1

which gives the terminal permission to access the serial ports of the jetson. On the raspi you can add yourself to the appropriate groups, so you have permissions once you restart the drone. You can:

sudo adduser $USER dialout
sudo adduser $USER tty

Check setup

1. Launch the initiate command

roslaunch quad_navigation initiate.launch

parameters you need to setup:

a) Inside vicon_bridge/launch/vicon.launch:

• specify the IP address of the machine that is publishing the vicon data
• specify the frame in which the data should be published. We have set it up to world b) Inside quad_navigation/launch/initiate.launch
• specify the address at which mavros communicates with the jetson

2. Check whether you are receiving vicon data

rostopic echo /vicon/<quad_name>/<quad_name>

Here you should check if the values increase as expected while you physically move the quad around

3. Check if the pixhawk is receiving the vicon data

rostopic echo /mavros/local_position/pose

and check that the vicon position is the same as the mavros estimated position Dont forget to check that the roll, pitch and yaw angles are also correct

4. Check that manual/stabilised flight modes are working reliably.

Running an experiment

1. Launch the initiate command

roslaunch quad_navigation initiate.launch

2. Launch the offboard node.

2a) If you wish to publish waypoints (ie x, y, z, and yaw angles)

rosrun quad_navigation offb_node

and you can publish desired waypoints to the topic /desired_setpoint, with messages of type geometry_msgs::Pose

2b) If you wish to publish velocities (ie vx, vy, vz and yaw_rates)

rosrun quad_navigation offb_velocity_node

and you can publish desired speeds to the topic /desiredVelocity, with messages of type of geometry_msgs::Twist

Note, I have defined the boundary of the net in our lab inside the code, and have a safety fitler onboard, such that based on the current position, the commanded velocity is modulated so the drone doesnt crash into the nets. Technically, one should verify the boundary of the nets each time the nets are set up.

3. Set RC to manual/stabilised mode, take off, and switch into offboard mode, when ready (Technically you dont need to take off, but if the yaw angle is off, it may not take off reliably.

Removing the telemetry modules, and communicating with QGC through Raspi

PX4 setup: each quadrotor has a unique MAV_SYS_ID. In this example it will be ID, defaults to 1. QGC setup (tested on v3.5.6 and newest): for each quadrotor, a separate UDP port is needed. Application Settings > Comm Links > Add and specify

• Name - a unique name for the drone
• Type=UDP
• Listening Port to a port number. Increment from the default = 14550.
• automatically connect on start = checked
• High Latency = unchecked and click ok.

and now

roslaunch mavros px4.launch fcu_url:=/dev/serial0:921600 gcs_url:=udp://:14555@<ip address of laptop>:<laptop/QGC UDP port> tgt_system:=<MAV_SYS_ID>

• Make sure QGC is running before you start mavros on the px4
• dont change MAV_COMP_ID and dont change 14555 on gcs_url.

Has been tested successfully with MAV_SYS_ID = 1, 3 with UDP ports laptop/QGC UDP port = 14550, 14551 simultaneously. We have also tried 14550, 14560.

See https://github.com/mavlink/mavros/tree/c13ceed94ce42f6c4ed961885d2b61466b5d1459/mavros for details on supported communication schema

Additional Notes:

1. In the cloned SD card for RPi, a newly flashed system connects to dd-wrt wifi by default. You can change it by editing /etc/netplan/50-cloud-init.yaml file
2. If you want to use ifconfig, install the following package first

sudo apt-get install net-tools

3. Sometimes ifconfig might show up error saying the user does not have administratrive privileges. You can give your user administrative priviliges and access to ifconfig files by running:

sudo usermod -aG sudo username
sudo ln -s /sbin/ifconfig /usr/bin/ifconfig