I turned this lesson into a Skee Ball challenge.  Using a paper box lid, exacto knife, paperclip holder, a ball, and a sharpie, I created a tournament where the groups would pair off and compete with each motor for several rounds.  The medium motor was able to earn 1, 5, or 10 points. The large motor was able to earn 5, 10, or 20 points (two different lids).  The students could fault if they touched the motor, ball, or lid (playing field) after they set up for the round.  Each team chose another team to sign off on the scorecard and keep everyone honest.  This exercise opened up a conversation about producing consistent results and building ridged frames. Scorecard attached below: