Participants make app-controlled fighting robots made from potatoes and other veggies and then they fight (and have a race if there's room). They use the PCB and motors from my Smartibot kit with some additional 3D printed bits so everything spikes into the vegetables. There's a video about the time I ran it at the Apple Store here: https://www.youtube.com/watch?v=EXbMMBYNRKg