ardrone_velocity

Introduction

Ardrone Velocity is a ROS Package for PID Velocity control of the AR.DRone 2.0. It is designed to work together with the ardrone_autonomy package.

Based on a velocity reference (given by the user) and a velocity measurement (obtained from ardrone_autonomy), this package implements a PID velocity controller of the Quadcopter. Since this controller depends on Wifi communication with the AR.Drone to obtain the velocity measurement, it won't be perfect due to delays in communication.

Dependencies

Requires an AR.Drone 2.0 Quadcopter and the ROS package ardrone_autonomy.

ROS Dependencies:

• ardrone_autonomy
• dynamic_reconfigure
• geometry_msgs
• roscpp
• rospy
• nav_msgs
• std_msgs.

Installation

Compile from source

• Install the ardrone_autonomy package following the instructions of their repository.

• Clone ardrone_velocity repository into the src folder of an existing or new catkin compatible workspace, and then build using catkin. To compile in ROS Indigo:

cd ~/catkin_ws/src
git clone https://github.com/raultron/ardrone_velocity.git
cd ~/catkin_ws
rosdep install --from-paths src -i
catkin_make

Usage

Launch the ardrone_autonomy driver (follow the instructions from the ardrone_autonomy documentation. This command works well with our package:

rosrun ardrone_autonomy ardrone_driver _realtime_navdata:=True _navdata_demo:=0 _looprate:=400

Then run the ardrone_velocity main PID controller node:

rosrun ardone_velocity pid_control

Units

All units and frames are [ROS REP 103]{http://www.ros.org/reps/rep-0103.html} compatible. Input velocity reference for the controller must be in m/s.

Parameters

• cmd_vel_ref_topic : The controller subscribes to this topic, expects a velocity reference published as a "Twist message" - Default: /cmd_vel_ref
• odometry_topic : The controller subscribes to this topic, expects a "Odometry Message" with the odometry information of the platform - Default: /ardrone/odometry
• cmd_vel_out_topic : The controller publish in this topic a "Twist message" with the controlled velocity to be sent to the platform - Default: /cmd_vel

Dynamic reconfiguration of PID Parameters

It is possible to reconfigure dynamically the following parameters:

• Kp_xy: Proportional Coefficient in X and Y direction - Default = 0.3
• Ki_xy: Integral Coefficient in X and Y direction - Default = 0.04
• Kd_xy: Derivative Coefficient in X and Y direction - Default = 0.05

Use the following command for convenient reconfiguration using a graphical user interface:

rosrun rqt_reconfigure rqt_reconfigure

The input of this package is a cmd_vel_pid Twist message with the required linear velocities in x,y,z in the quadcopter frame and the required angular velocity around z.

The output of this package is a cmd_vel Twist message, all the values should be between (-1;+1) since that is expected by the Ardrone SDK (implemented in ROS by ardrone_autonomy package). The Ardrone SDK interprets the signals as follows:

• phi (left-right angle): cmd_vel.linear.x
• theta (front-back angle): cmd_vel.linear.y
• gaz (up-down vertical speed): cmd_vel.linear.z
• yaw (Angular speed around Z axis): cmd_vel.angular.z

As stated in the Ardrone SDK Developers Manual:

"In order to allow the user to choose between smooth or dynamic moves, the arguments of this function are not directly the control parameters values, but a percentage of the maximum corresponding values as set in the drone parameters. All parameters must thus be floatingpoint values between −1.0 and 1.0."