Hands-On ROS for Robotics Programming

Composing motions

We have already learned how to find the actual X, Y, and Z axes of the robot. Go back to Chapter 4, Creating the Virtual Two-Wheeled ROS Robot, the Building a differential drive robot with URDF section, if you need to remember how.

Keeping their orientations in mind, let's design a more complex trajectory by combining both translation (linear X) and rotation (angular Z). The goal is to get GoPiGo3 to follow a circumferential path that has a 0.25 m radius at a speed of 45º/s:

• The angular Z speed is 45º/s = 0.785 rad/s. We just need to change units from sexagesimal degrees to radians.
• The linear X speed can be obtained by multiplying the requested radius by the angular speed; that is, 0.25 m * 0.785 rad/s = 0.196 m.

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