All the best designs start on the back of an envelope, and here’s ours. Literally it was a quick sketch I scribbled on the back of some paper hurriedly plucked from the recycling box to demonstrate the principle to my sons. Once they saw, they understood and, with both of them on message, we could proceed to the next stage. To help them understand the principles of structures and also so they can have some design input, the plan is to build a cardboard model of the chassis. Currently we are recruiting our scale subject, one Action Man toy.