I’d like you to meet Tumble Buggy — class mascot and most used piece of lab equipment in 9th grade Physics 1. We use this puppy through nearly all of mechanics. For years, I’ve wished I could select a velocity other than fast or slow. Enter the Variable Velocity Tumble Buggy!

Using an inexpensive DC motor controller, I made the following proof-of-concept. Maybe I’ll tidy things up by installing the controller into the decorative cover of the car. I personally think having the knob stick out the tail end of the car would be cute.

The motor controller is sold in a 6 pack here. I’d love to hear if you find it sold elsewhere.