Click a yellow button to add a new part. Click on a component to change it. Place gears close together (but not too close) to make them engage. Play with the ratios to change the speed. Use a gear with a spindle to add gears together or to put a cam on a gear. Now added pistons. You will need a Crank, a Connecting Rod and a Piston Head, all can be found in the Gears Section.
All credit to @SohCahToa314 ( =
