K.I.S.S.

Do you know what KISS means?  It means keep it simple (stupid).  You have been thinking of things that can be propelled along the ground.  Is that the only direction things can be propelled?  Do things need to stay on the ground?  There are very easy, creative solutions for you to solve this part of the challenge with all the materials we already have, with a device that could be built in 5 minutes, by anyone who gives it a minute or two of thought.  

See you Monday.  6:30.