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Connect gamepad directly to the robot

We bought the Logitech 710 with a USB dongle. Allows running /joy_node from the bot, less lag, no need to carry the laptop around.

Write a Python node to monitor /joy topic and send commands to the Arduino

I wrote joy_subscriber.py

To get a mapping of your gamepad:

(T1):$ ros2 run joy joy_node
(T2):$ ros2 topic echo /joy

The Logitech 710 has two modes: X and D. Instructions recommend mode X but the mapping seems strange. Note for example Left joystick only has discrete values in mode X. Note also that MODE and VIBRATION do not trigger any response in /joy topic

Mode X Mode D
buttons[0] A X
buttons[1] B A
buttons[2] X B
buttons[3] Y Y
buttons[4] LB LB
buttons[5] RB RB
buttons[6] BACK LT
buttons[7] START RT
buttons[8] ? BACK
buttons[9] Left Stick Push on START
buttons[10] Right Stick Push on Left Stick Push on
buttons[11] Right Stick Push on
axes[0] Cross Left/Right. Discrete values Left= +1. None = 0, Right = -1 Left Stick Left/Right. Float values from +1 (Left) to -1 (Right)
axes[1] Cross Up/Down. Discrete values Up = +1, None = 0, Down = -1 Left Stick Up/Down. Float values from +1 (Up) to -1 (Down)
axes[2] LT. Float values from +1 (Not pressed) to -1 (Fully pressed) Right Stick Left/Right. Float values from +1 (Left) to -1 (Right)
axes[3] Right Stick Left/Right. Float values from +1 (Left) to -1 (Right) Right Stick Up/Down. Float values from +1 (Up) to -1 (Down)
axes[4] Right Stick Up/Down. Float values from +1 (Up) to -1 (Down) Cross Left/Right. Discrete values Left= +1. None = 0, Right = -1
axes[5] RT. Float values from +1 (Not pressed) to -1 (Fully pressed) Cross Up/Down. Discrete values Up = +1, None = 0, Down = -1
axes[6] Left Stick Left/Right. Discrete values Left= +1. None = 0, Right = -1
axes[7] Left Stick Up/Down. Discrete values Up = +1, None = 0, Down = -1

Fix the project to compile the node joy_subscriber.py.

I found the fix here: https://answers.ros.org/question/299269/ros2-run-python-executable-not-found/

  • Add the Python source file to sevillabot/scripts

  • Add an empty __init__.py file in the folder sevillabot/scripts

  • Make sure the file is executable with chmod +x joy_subscriber.py

  • Make sure the first line of code is the python shebang: #!/usr/bin/env python3

  • In CMakeLists.txt:

# Install Python executables
ament_python_install_package(scripts)

...

install(
	PROGRAMS scripts/joy_subscriber.py  
  	DESTINATION lib/${PROJECT_NAME} 
  )

Apparently mixing CPP and python in a package is a big deal, see more details here: https://roboticsbackend.com/ros2-package-for-both-python-and-cpp-nodes/

Not sure how I got it to work the first time but I am pretty sure I didnt add the install ( PROGRAMS... part.

To compile:

$ cd ~/robot_ws
$ colcon build --symlink-install 
$ source install/setup.bash

Quick start

To run you need to open several ssh terminals, source and run different nodes:

(bot1):$ ros2 launch sevillabot launch_robot.launch.py # spawns bot
(bot2):$ ros2 launch sevillabot joystick.launch.py # launches joy_node and teleop_node with params and remapping of cmd_vel
(bot3):$ ros2 run sevillabot joy_subscriber.py # launch joy_subscriber

Note on unique Arduino addresses

/dev/ttyUSB* depends of plugging order

/dev/serial/by-id/* is supposedly an unique ID but all my Arduino nanos share the same!: /dev/serial/by-id/usb-1a86_USB2.0-Ser_-if00-port0

/dev/serial/by-path/* depends on where the device is physically connected (which USB port). Could work if we assign dedicated USB ports to specific Arduinos and are consistent with it.

RPi4 USB port position /dev/serial/by-path/* address of Arduino nano
top right /dev/serial/by-path/platform-fd500000.pcie-pci-0000:01:00.0-usb-0:1.1:1.0-port0
bottom right /dev/serial/by-path/platform-fd500000.pcie-pci-0000:01:00.0-usb-0:1.2:1.0-port0
top right /dev/serial/by-path/platform-fd500000.pcie-pci-0000:01:00.0-usb-0:1.3:1.0-port0
bottom left /dev/serial/by-path/platform-fd500000.pcie-pci-0000:01:00.0-usb-0:1.4:1.0-port0

Found using:

$ ls -l /dev/ttyUSB* # detects serial devices
$ udevadm info /dev/ttyUSB0 # gets info for each device

Assignment of sevillabot USB ports: Arduino for Base robot in 1, Addon Arduino in 2, Gamepad dongle in 3, 4 is spare

Modified both ros2_control.xacro and joy_subscriber.py to use /dev/serial/by-path/* instead of /dev/ttyUSB* or /dev/serial/by-id/*

And now it works!

Note: the stepper motor just waiting consumes ~0.25A*12V = 3W!! And it gets hot!!

--

After installing the Mega, the addresses by-id remain unchanged, but by-path addresses change:

Mega4 USB port position (when plugged on top-right RPi USB port) /dev/serial/by-path/* address
left: Addon Arduino microUSB, ej. LiDAR, gun /dev/serial/by-path/platform-fd500000.pcie-pci-0000:01:00.0-usb-0:1.2.3:1.0-port0
center: gamepad dongle /dev/serial/by-path/platform-fd500000.pcie-pci-0000:01:00.0-usb-0:1.2.2:1.0-port0
right: robot base Arduino /dev/serial/by-path/platform-fd500000.pcie-pci-0000:01:00.0-usb-0:1.2.1:1.0-port0
side: Addon Arduino miniUSB ej. clamp, line follower /dev/serial/by-path/platform-fd500000.pcie-pci-0000:01:00.0-usb-0:1.2.4:1.0-port0