Working with radians, Multiple Robots and Custom Messages

Plan for today

  • This lab will be a guided team programming session. You will be in a breakout room with your teammates and collaborate on the solutions.
  • Please do the following during lab while we are around to help everyone solve their problems.
  • The goal is that it takes 90 minutes but if you need the extra 30 minutes we will stick around

<%= callout(“NB”, “ After completing each section, invite a TA into your breakout room so they can sign off”, :small) %>

Sections

  1. Write this function, and write test cases for it.

<%= source_begin “language-python” %>

def best_turn_direction(current, target): “"”Given a current orientation and a target orientation, return optimal direction to turn.

 current -- current orientation in radians (positive or negative)
 target -- target orientation in radians (positive or negative)

 Returns:
 +1 if it's best to turn counterclockwise
 -1 if it's best to turn clockwise
 0 if no turn is required

 Examples:

 best_turn_direction(0, PI/2) => +1
 best_turn_direction(PI/2, 0) => -1
 best_turn_direction(PI/2, -PI/2) => -1
 best_turn_direction(-PI/2, PI/2) => +1
 (but there are much trickier cases)   """ <%= source_end %>

  1. Create a Gazebo world with three simulated robots in it, and write a very simple ROS program ti make them move. The simplest is if they all just respond to cmd_vels identically. So if they start next to each other, in theory they would all move together. Here is a page out of our Lab notebook which in turn has two further links.

  2. Define a custom message (.msg), make the appropriate updates to CMakeFile and Package.xml. Write a trivial script that includes it so you can show the the python builds: Here’s one reference, but there are many more: Defining Custom Messages