This is a 3 speed transmission with reverse. This transmission is designed to work and transmit real power. It uses dog clutches and an H box. I designed this for the latest revision of my steam kart, which will be using an air drill for the engine. The ratios are 3.15:1, 1.25:1, 1:1.6, and reverse is 4.0:1. I have included both straight cut gears and herringbone gear stl files. The shafts are square rods because the dog clutches need to slide on them but still transmit torque, and there's really no other cheap way to do that.

You will also need some hardware: 8x 6-32 x 3/4" screws 2x 5/16 x 1ft threaded rod 6x 8-32 x 1ft threaded rod 2x 3/8in x 1ft square rod 4x 6-32 x 2 3/4in bolts (or 4 pieces of 6-32 threaded rod and 4 6-32 nuts) 5/16 nuts 8-32 wingnuts 1x 5mm x ~40mm bolt and nylock nut, for the reverse idler

8x 6003 bearing (17mm x 35mm x 10mm), Open bearing or SS is preferrable for minimum friction. 2x MR105 bearing (5mm x 10mm x 4mm), for the reverse idler