Gear train simulator in 3D: build a simple train of 2 to 4 gears, with idler gears, or a compound train of 1 to 4 stages, driven by an electric motor. Choose the teeth of each gear, the motor power and speed and the efficiency of each pair, and the panel works out the gear ratio (the product of the driven gears over the product of the driving gears) and the speed, power and torque of each shaft. It warns you when two gears collide and includes the worked examples from my notes.