# Companion Computer This section introduces how to set up the (on-board) companion computer for PX4-based drones. ### Hardware Connection #### FTDI Devices / Logic Level Shifters * Connect onboard computer and Pixhawk flight controller via an FTDI Chip USB-to-serial adapter. * use the `TELEM2` port on Pixhawk and a USB port on companion computer * make sure the FTDI chip or logic level shifter is compatible in our use case * see [this section](https://docs.px4.io/master/en/peripherals/companion_computer_peripherals.html#ftdi-devices) for recommended ones (Pixdev discontinued though) * make sure the pin-to-pin connection is correct * out of 6 pins, 3 pins must be connected (TX-RX, RX-TX, GND-GND) * the red power pin must not be connected * CTS and RTS pins are optional; for the use of so called "flow control" for Pixhawk * see [this section](https://docs.px4.io/master/en/companion_computer/pixhawk_companion.html#hardware-setup) for the full wiring table * It is recommended that the FTDI chip operates at 3.3V, but not required * the red power pin is not connected anyway * according to [this section](https://docs.px4.io/master/en/companion_computer/pixhawk_companion.html#hardware-setup) in PX4 docs, all Pixhawk serial ports operate at 3.3V and are 5V level compatible. * Example: [USB FTDI Serial to JST-GH (Basic)](https://store.mrobotics.io/USB-FTDI-Serial-to-JST-GH-p/mro-ftdi-jstgh01-mr.htm) * warning: this product is not a ready-to-go adapter; need to switch RX and TX cables (cut them off and then solder together) * see [this video](https://www.youtube.com/watch?v=NSqPHQ1zQco) for a quick recap about soldering two wires together * soldering quality can also affect the performance; bad soldering will lead to high noise level in the communication * the connection link is: computer --- USB port --- USB to micro USB cable --- micro USB port --- FTDI chip --- 6-pin JST port --- JST cable --- 6-pin TELEM2 port --- Pixhawk ![(left) FTDI cable after soldering (right) final cable after hot-glue gun and heat-shrink tubing](https://3310611219-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LwRt8_BWYScDaMKj3wZ%2F-MfBXyfncaVxaRivMU44%2F-MfBZWQYRRdZrZfuP0UH%2FPX4_FTDI_Connection.PNG?alt=media\&token=8a094ce4-3922-45b7-9fb0-d7b1ed2d30c5) #### WiFi Router Need to prepare a high-speed low-latency WiFi router * edit settings to shrink DHCP range and leave a range of IP addresses unused for static IP * in my case, I use `192.168.0.21` for onboard computer and `192.168.0.121` for gcs computer ### PX4 Firmware * Need to enable MAVLink on a configurable serial port (typically `TELEM2`). * Connect the Pixhawk flight controller to QGroundControl via USB or Telemetry (TELEM1), so that you can change parameters in the parameter table and push them to the vehicle. * Set param MAV\_1\_CONFIG = `TELEM 2` (MAV\_1\_CONFIG is often used to map the TELEM 2 port) * Reboot the vehicle to make other parameters visible. * Set the remaining parameters if not being set by default. * MAV\_1\_MODE = `Onboard` * SER\_TEL2\_BAUD = `921600` (921600 or higher recommended for applications like log streaming or FastRTPS) * Once this parameter is enabled, when Pixhawk is powered on, it will automatically broadcast messages (drone status) via TELEM2 port. The RX indicator should be flickering accordingly. ### Onboard Computer * Set up a static IP address for WiFi connection * in my case, I use `192.168.0.21` for onboard computer and `192.168.0.121` for gcs computer * optional: edit `hosts` file by `sudo gedit /etc/hosts` and add item `192.168.0.121 arcs-gcs` * udev rule: create a new file at `/etc/udev/rules.d/99-pixhawk.rules` with the following content * double check by `lsusb` the actual vendor and product ID of the FTDI chip ```bash # NOTE: use the actual vendor and product IDs (check it by lsusb) SUBSYSTEM=="tty", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6015", SYMLINK+="ttyPixhawk" #SUBSYSTEM=="tty", ATTRS{idVendor}=="1a86", ATTRS{idProduct}=="7523", SYMLINK+="ttyPixhawk" # optional; can be omitted if Arduino is not being used SUBSYSTEM=="tty", ATTRS{idVendor}=="2341", ATTRS{idProduct}=="0042", SYMLINK+="ttyArduino" ``` * Add current user to the `tty` and `dialout` groups to avoid to have to execute scripts as root ``` sudo usermod -a -G tty sudo usermod -a -G dialout ``` * Launch file is the same as `mavros/launch/px4.launch` except for the following modifications * set `fcu_url` to `/dev/ttyPixhawk:921600` * set `gcs_url` to `udp://@arcs-gcs:14550` * double check if `tgt_system` matches `MAV_SYS_ID` parameter in PX4 firmware (default 1) * double check if `tgt_component` matches `MAV_COMP_ID` parameter in PX4 firmware (default 1) ### Ground Control Station (GSC) Computer * Set up a static IP address for WiFi connection * in my case, I use `192.168.0.21` for onboard computer and `192.168.0.121` for gcs computer * optional: edit `hosts` file by `sudo gedit /etc/hosts`and add item `192.168.0.21 arcs-robot` * optional: set up password-free SSH login by `ssh-copy-id arcs@arcs-robot` * Download QGroundControl Ubuntu amd64 build (arm architecture is not supported) * run `./QGroundControl` and you can see drone status * it will automatically listen to port 14550 for UDP connections ## Troubleshooting #### Hardware connection * `lsusb` check the vendor ID and product ID of FTDI chip * `ls -l /dev/ttyPixhawk` check the read/write permission * use a multi-meter to check voltage level * find a chip that has TX/RX indicators to help debugging #### mavros connection * `rostopic echo -n1 /diagnostics` * `rosrun mavros checkid` #### Issue: FCU not connected * If TELEM2 port is indeed broadcasting messages, then `cat /dev/ttyPixhawk` should print out random symbols/streaming and `rostopic echo -n1 /diagnostics` should have RX packages/bytes received. * See [this issue in mavros repository](https://github.com/mavlink/mavros/issues/1592) for more details. ## References * PX4 docs: [Companion Computer Peripherals](https://docs.px4.io/master/en/peripherals/companion_computer_peripherals.html) * PX4 docs: [Companion Computer for Pixhawk Series](https://docs.px4.io/master/en/companion_computer/pixhawk_companion.html) * PX4 docs: [MAVLink Peripherals (GCS/OSD/Companion)](https://docs.px4.io/master/en/peripherals/mavlink_peripherals.html) * PX4 docs: [Serial Port Configuration](https://docs.px4.io/master/en/peripherals/serial_configuration.html) * Holybro docs: [Pixhawk 4 Pinout Manual](http://www.holybro.com/manual/Pixhawk4-Pinouts.pdf) ## Examples for Healthy/Successful Connections #### roslaunch mavros px4.launch ``` auto-starting new master process[master]: started with pid [25993] ROS_MASTER_URI=http://localhost:11311 setting /run_id to 52bef7b4-ea8d-11eb-b0f6-204ef6c5ef8f process[rosout-1]: started with pid [26011] started core service [/rosout] process[mavros-2]: started with pid [26029] [ INFO] [1626917830.064227539]: FCU URL: /dev/ttyPixhawk:921600 [ INFO] [1626917830.075512530]: serial0: device: /dev/ttyPixhawk @ 921600 bps [ INFO] [1626917830.077993842]: GCS URL: udp://@arcs-gcs:14550 [ INFO] [1626917830.079239602]: udp1: Bind address: 0.0.0.0:14555 [ INFO] [1626917830.079788274]: udp1: Remote address: 192.168.0.121:14550 [ INFO] [1626917830.123951216]: Plugin 3dr_radio loaded [ INFO] [1626917830.133589392]: Plugin 3dr_radio initialized [ INFO] [1626917830.134123504]: Plugin actuator_control loaded ... [ INFO] [1626917831.596142837]: Plugin wind_estimation loaded [ INFO] [1626917831.599738645]: Plugin wind_estimation initialized [ INFO] [1626917831.599962517]: Autostarting mavlink via USB on PX4 [ INFO] [1626917831.600359957]: Built-in SIMD instructions: ARM NEON [ INFO] [1626917831.600489557]: Built-in MAVLink package version: 2021.3.3 [ INFO] [1626917831.600601205]: Known MAVLink dialects: common ardupilotmega ASLUAV all autoquad icarous matrixpilot paparazzi standard uAvionix ualberta [ INFO] [1626917831.601232277]: MAVROS started. MY ID 1.240, TARGET ID 1.1 [ INFO] [1626917831.607340148]: IMU: High resolution IMU detected! [ INFO] [1626917831.623283188]: IMU: Attitude quaternion IMU detected! [ INFO] [1626917831.712271824]: CON: Got HEARTBEAT, connected. FCU: PX4 Autopilot [ INFO] [1626917831.726061328]: IMU: High resolution IMU detected! [ INFO] [1626917831.727046608]: IMU: Attitude quaternion IMU detected! [ INFO] [1626917832.734570666]: GF: Using MISSION_ITEM_INT [ INFO] [1626917832.734848618]: RP: Using MISSION_ITEM_INT [ INFO] [1626917832.735039114]: WP: Using MISSION_ITEM_INT [ INFO] [1626917832.735182506]: VER: 1.1: Capabilities 0x000000000000e4ef [ INFO] [1626917832.735327146]: VER: 1.1: Flight software: 010b03ff (a6274bc5ed000000) [ INFO] [1626917832.735467946]: VER: 1.1: Middleware software: 010b03ff (a6274bc5ed000000) [ INFO] [1626917832.735595530]: VER: 1.1: OS software: 080200ff (ec20f2e6c5cc35b2) [ INFO] [1626917832.735720650]: VER: 1.1: Board hardware: 00000032 [ INFO] [1626917832.735841738]: VER: 1.1: VID/PID: 26ac:0032 [ INFO] [1626917832.736006506]: VER: 1.1: UID: 4356500d20383058 [ WARN] [1626917832.736531306]: CMD: Unexpected command 520, result 0 [ INFO] [1626917837.984168559]: udp1: Remote address: 192.168.0.121:14550 [ WARN] [1626917837.999627759]: FCU: Preflight: GPS Speed Accuracy too low [ INFO] [1626917838.736300702]: VER: 1.1: Capabilities 0x000000000000e4ef [ INFO] [1626917838.736565246]: VER: 1.1: Flight software: 010b03ff (a6274bc5ed000000) [ INFO] [1626917838.736837118]: VER: 1.1: Middleware software: 010b03ff (a6274bc5ed000000) [ INFO] [1626917838.737020766]: VER: 1.1: OS software: 080200ff (ec20f2e6c5cc35b2) [ INFO] [1626917838.737107582]: VER: 1.1: Board hardware: 00000032 [ INFO] [1626917838.737212190]: VER: 1.1: VID/PID: 26ac:0032 [ INFO] [1626917838.737322942]: VER: 1.1: UID: 4356500d20383058 [ INFO] [1626917838.929431802]: WP: seems GCS requesting mission [ INFO] [1626917838.929658650]: WP: scheduling pull after GCS is done [ INFO] [1626917838.957424154]: GF: seems GCS requesting mission [ INFO] [1626917838.957704026]: GF: scheduling pull after GCS is done [ INFO] [1626917838.984743641]: RP: seems GCS requesting mission [ INFO] [1626917838.984973657]: RP: scheduling pull after GCS is done [ INFO] [1626917841.716082666]: HP: requesting home position [ INFO] [1626917843.932448880]: WP: mission received [ INFO] [1626917843.961392944]: GF: mission received [ INFO] [1626917843.987520816]: RP: mission received [ INFO] [1626917845.005917544]: PR: parameters list received [ INFO] [1626917851.715933397]: HP: requesting home position [ INFO] [1626917861.715935981]: HP: requesting home position [ INFO] [1626917871.715917420]: HP: requesting home position ``` #### rostopic echo -n1 /diagnostics ``` header: seq: 461 stamp: secs: 1626918167 nsecs: 602185190 frame_id: '' status: - level: 0 name: "mavros: FCU connection" message: "connected" hardware_id: "/dev/ttyPixhawk:921600" values: - key: "Received packets:" value: "2169" - key: "Dropped packets:" value: "0" - key: "Buffer overruns:" value: "0" - key: "Parse errors:" value: "0" - key: "Rx sequence number:" value: "98" - key: "Tx sequence number:" value: "0" - key: "Rx total bytes:" value: "7954038" - key: "Tx total bytes:" value: "194865" - key: "Rx speed:" value: "36628.000000" - key: "Tx speed:" value: "875.000000" - level: 0 name: "mavros: GPS" message: "3D fix" hardware_id: "/dev/ttyPixhawk:921600" values: - key: "Satellites visible" value: "9" - key: "Fix type" value: "3" - key: "EPH (m)" value: "0.95" - key: "EPV (m)" value: "2.03" - level: 0 name: "mavros: Heartbeat" message: "Normal" hardware_id: "/dev/ttyPixhawk:921600" values: - key: "Heartbeats since startup" value: "336" - key: "Frequency (Hz)" value: "1.000000" - key: "Vehicle type" value: "Quadrotor" - key: "Autopilot type" value: "PX4 Autopilot" - key: "Mode" value: "AUTO.LOITER" - key: "System status" value: "Standby" - level: 2 name: "mavros: System" message: "Sensor health" hardware_id: "/dev/ttyPixhawk:921600" values: - key: "Sensor present" value: "0x122E002F" - key: "Sensor enabled" value: "0x1221002F" - key: "Sensor health" value: "0x022E002F" - key: "3D gyro" value: "Ok" - key: "3D accelerometer" value: "Ok" - key: "3D magnetometer" value: "Ok" - key: "absolute pressure" value: "Ok" - key: "GPS" value: "Ok" - key: "rc receiver" value: "Fail" - key: "AHRS subsystem health" value: "Ok" - key: "Battery" value: "Ok" - key: "pre-arm check status. Always healthy when armed" value: "Fail" - key: "CPU Load (%)" value: "41.4" - key: "Drop rate (%)" value: "0.0" - key: "Errors comm" value: "0" - key: "Errors count #1" value: "0" - key: "Errors count #2" value: "0" - key: "Errors count #3" value: "0" - key: "Errors count #4" value: "0" - level: 0 name: "mavros: Battery" message: "Normal" hardware_id: "/dev/ttyPixhawk:921600" values: - key: "Voltage" value: "16.22" - key: "Current" value: "0.5" - key: "Remaining" value: "83.0" - level: 0 name: "mavros: Time Sync" message: "Normal" hardware_id: "/dev/ttyPixhawk:921600" values: - key: "Timesyncs since startup" value: "3361" - key: "Frequency (Hz)" value: "10.000005" - key: "Last RTT (ms)" value: "1.375040" - key: "Mean RTT (ms)" value: "2.221804" - key: "Last remote time (s)" value: "384.336849000" - key: "Estimated time offset (s)" value: "1626917783.223483801" --- ``` #### rosrun mavros checkid ``` OK. I got messages from 1:1. --- Received 6190 messages, from 1 addresses sys:comp list of messages 1:1 0, 1, 2, 4, 140, 141, 147, 24, 30, 31, 32, 33, 36, 74, 331, 76, 83, 340, 85, 230, 105, 111, 241, 242, 245 ```