A good base has a little weight to it, sits perfectly flat on a table and allows for a dowel to be sunk into it. If using a small block of wood, for example, drill a slightly undersized hole in the center, add a dab of wood glue and tap the dowel into place. I got lucky and had a few valve handles lying around, one of which my colored pencil fit snugly in to.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.