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A simple robot drive system that includes skid steering joystick teleoperation, control of a panning servo to look around the robot, and Arduino firmware.
- Maintainer status: maintained
- Maintainer: Daniel Snider <danielsnider12 AT gmail DOT com>
- Author: Daniel Snider <danielsnider12 AT gmail DOT com>, Matthew Mirvish <matthewmirvish AT hotmail DOT com>
- License: Unlicense
- Source: git https://github.com/danielsnider/simple_drive.git (branch: master)
A simple robot drive system. Features include:
- skid steering joystick teleoperation with three drive speeds
- joystick control of a servo (left and right only)
- dedicated left and right thumbsticks for left and right wheel speeds
- a cmd_vel multiplexer to support a coexisting autonomous drive system
- simple Arduino firmware to talk to PWM motors and a servo
This package does not do the following:
This package is divided into four parts:
Drive your robot with a joystick in skid steering mode (also known as diff drive or tank drive). Left joystick thumbstick controls left wheels, right thumbstick controls right wheels.
Motor commands from multiple sources are forwarded with a preference for human control over autonomous commands.
Send motor commands to your microcontroller.
Microcontroller software that controls your motors. Not a ROS node.
Package created by Ryerson University students for the University Rover Competition, summer 2017.
$ sudo apt-get install ros-kinetic-simple-drive
2. Launch ROS nodes:
$ roslaunch simple_drive drive_teleop.launch joy_dev:=/dev/input/js0 $ roslaunch simple_drive cmd_vel_mux.launch $ roslaunch simple_drive simple_drive.launch serial_dev:=/dev/ttyACM0 OR all-in-one launch: $ roslaunch simple_drive drive.launch
3. Install the drive_firmware onto a microcontroller connected to motors and wheels by PWM. The microcontroller must also be connected to the computer running the simple_drive ROS node by a serial connection (ex. USB).
4. Drive your robot around.
This diagram is also available in Visio format.
This node converts sensor_msgs/Joy messages from the joy node into a variety of commands to drive the robot at low, medium, and high speed, look around with a servo, and cancel move_base goals at any moment. This node simply sends commands to other nodes. Typically the servo is used to move a camera so that the teleoperator can look around the robot.
The button mapping was tested on an Xbox 360 controller and should require little or no modification for similar controllers.
$ roslaunch simple_drive drive_teleop.launch joy_dev:=/dev/input/js0
Subscribed Topicsjoy (sensor_msgs/Joy)
- Controller joystick button presses are received on this topic. See joy node for more info.
Published Topicsteleop/cmd_vel (geometry_msgs/Twist)
- Output motion commands that drive the robot.
- Output servo commands that control the angle of a servo.
Parameters~servo_pan_speed (int, default: 5)
- The degrees of servo motion per button press.
- The maximum angle of servo rotation in degrees.
- The minimum angle of servo rotation in degrees.
The cmd_vel_mux node receives movement commands on two sensor_msgs/Twist topics, one for teleoperation and one for autonomous control, typically move_base. Movement commands are multiplexed to a final topic for robot consumption. If any teleoperation command is received autonomous commands are blocked for a set time defined by the block_duration parameter.
$ roslaunch simple_drive cmd_vel_mux.launch
Subscribed Topicsteleop/cmd_vel (geometry_msgs/Twist)
- Human generated movement commands from a teleoperation node such as the drive_teleop node.
Published Topicscmd_vel (geometry_msgs/Twist)
- Movement commands for consumption by the robot. Autonomous movement commands will be blocked for block_duration seconds if any teleoperation command is received.
Parameters~block_duration (int, default: 5)
- The amount of time autonomous movement is blocked after any human movement is received.
This node communicates with the drive_firmware using a custom serial protocol described below. An example serial data packet could be 0,0.5,0.5 which would mean drive motors forward at half speed and rotate at half speed.
Serial data packet
Twist motor command
(BYTE) 0, (FLOAT) LINEAR_VELOCITY, (FLOAT) ANGULAR_VELOCITY
Servo position command
(BYTE) 2, (FLOAT) SERVO_ANGLE
If your microcontroller supports subscribing to ROS twist messages (Arduinos can use rosserial_arduino) then it would be simpler to do that and skip this node. However, this node is written in python so you could more easily add complex functionality in python and then in your microcontroller do the minimum amount of work necessary.
$ roslaunch simple_drive simple_drive.launch serial_dev:=/dev/ttyACM0
Subscribed Topicscmd_vel (geometry_msgs/Twist)
- Motor commands received on this topic are encoded and sent over serial to the drive_firmware.
- Servo position commands received on this topic are encoded and sent over serial to the drive_firmware.
Parameters~serial_dev (string, default: /dev/ttyACM0)
- The microcontroller, often an Arduino, as seen in linux, that this node will send motor commands to.
- Sets the serial device data transmission rate in bits per second (baud).
The drive_firmware microcontroller code does the minimum amount of work possible to receive motor commands from a USB serial connection and output voltages to digital PWM output to be received by motor controllers.
We connected an Arduino by USB serial to our main robot computer. We tested on a Arduino Mega 2560 and Arduino Due, however many other boards should work with the same code and setup steps thanks to PlatformIO. You may need to change to change the pin numbers.
Caution! This software does not stop moving the robot if no messages are received for certain period of time. A pull request for this is very welcome.
We deploy the drive_firmware to an Arduino microcontroller using PlatformIO.
Install and configure drive_firmware
This steps were tested on Ubuntu 16.04.
1. Install PlatformIO
$ sudo python -c "$(curl -fsSL https://raw.githubusercontent.com/platformio/platformio/master/scripts/get-platformio.py)" # Enable Access to Serial Ports (USB/UART) $ sudo usermod -a -G dialout <your username here> $ curl https://raw.githubusercontent.com/platformio/platformio/develop/scripts/99-platformio-udev.rules > /etc/udev/rules.d/99-platformio-udev.rules # After this file is installed, physically unplug and reconnect your board. $ sudo service udev restart
More PlatformIO install info: http://docs.platformio.org/en/latest/installation.html#super-quick-mac-linux
2. Create a PlatformIO project
$ roscd simple_drive $ cd ./drive_firmware/ # Find the microcontroller that you have in the list of PlatformIO boards $ pio boards | grep -i mega2560 # Use the name of your board to initialize your project $ pio init --board megaatmega2560
More PlatformIO info: http://docs.platformio.org/en/latest/quickstart.html
3. Modify wiring if necessary
$ vim src/main.cpp +4
Depending on how you want to wire your microcontroller this wiring could be changed:
4. Modify PWM Settings
$ vim src/main.cpp +17
Edit the following section to match your motor controller PWM specs:
5. Deploy Code to Arduino
$ pio run --target upload
6. Drive your robot!
Other Implementation Details
Tank to Twist Calculation
When a left and right joystick inputs are received by the drive_teleop node, representing left and right wheel velocities (ie. skid steering or differential drive), a geometry_msgs/Twist with linear and rotational velocities is calculated as:
- Linear velocity (m/s) =
(left_speed + right_speed) / 2.0
- Angular velocity (rad/s) =
(right_speed - left_speed) / 2.0
Twist to Tank Calculation
- Left wheel velocity (m/s) =
linear_speed + angular_speed
- Right wheel velocity (m/s) =
linear_speed - angular_speed
Similar to simple_drive:
http://wiki.ros.org/differential_drive - Differential drive software with support for a velocity PID target, a small GUI to control the robot, and more.
Similar to drive_teleop:
http://wiki.ros.org/teleop_twist_joy - This teleop node converts joy messages to twist messages.
http://wiki.ros.org/joy_teleop - This teleop node takes joy messages and publishes topics or calls actions according a configuration file.
Similar to cmd_vel_mux:
http://wiki.ros.org/twist_mux - Multiplex several velocity command topics with prioritization or disabling according to a configuration file.
Feature requests, bug reports, and contributions are welcome at https://github.com/danielsnider/simple_drive.
Special thanks to anyone who sends a picture of this package in action on their robot!