Every robot is one circuit board — round, triangular, square or hexagonal, alone or slotted into one or two more — with solar cells, one or two Tilden solar engines (a capacitor that charges in the lamp light and fires a motor, an N20 or planetary gear motor with spokes, or a solenoid when its trigger voltage is reached) and a few wires: legs, spikes or a rolling cage. The best are the simple ones that move, stack and interlock and get up on each other by themselves. Each robot is tested with a twin: dropped onto it four times (does it stay on top? how hard a sideways push does it hold — friction alone holds about 0.35 g, more is shape), side by side under the lamp for 20 s (does one climb or jump onto the other?), and alone for 30 s (how far does it get?). Score = stack + 2 × climb + rise + 0.3 × touch + 0.5 × jump + move (rise: how far one lifts itself on the other; touch: how long they touch); merit = score × simplicity. Your browser keeps the best of each kind in the map (MAP-Elites, Mouret & Clune 2015) and mutates them. A run starts from designed robots — a hopper, a wheg walker and a twin wheg, laid out from physics (designs.js) — then adds random ones. Physics, parts and sources: engines/beam-v1/. The run is kept in this browser. [S] saves the selected robot for the arena; [E] downloads it as JSON.