Step 6: Tail Wheel
As of now, your robot is probably awkwardly leaning backwards... that's why it is time to insert the tail wheel! Take the little black ball, and line the holes in its side up with the holes on the back of the robot (see pictures). Then, insert the cotter pin through all these holes, and fold up the two ends so that it can't come out. Now you're robot should stand level, and have a low friction caster for turning.