I have video from one more activity in Amazing Cardboard Tube Science. This shows one of my first attempts at the car for On a Roll on page 20.
The force of the air coming from the balloon is almost too weak to get the car moving. So weak, in fact, that when I put a passenger in the car, the balloon deflated without the car moving at all. I later determined that the problem was in my axles. They weren’t exactly parallel, so they wasted a lot of energy working against each other. One of them was also not centered in the middle of the wheel.
Testing your designs and improving them is an important part of the engineering design cycle. If you don’t get exactly the results you are hoping for, keep working!
Student Challenge: Build the car on page 20. Once you get it moving, try adding a passenger (such as a Playmobile or Lego figure). Can you make the car work efficiently enough to carry the extra load?
I’d love to see your results!