I've added a guide on how the example solution to the homework of lesson 3 works, it is now up here as lesson 4.

Our little rover can move and steer now!

The "homework" for part 3 of the tutorial ended up being much harder than I thought it would be (although a lot of that was me being too lazy to do it well at first, so I had to redo it), so part 4 of the tutorial will be going over this example solution to part 3, and then we will continue with doing some other plugin types (sensors are coming soon).