Simple Robot Car Wheel drive Train / Gearbox

Goal

Simple Robots are a great tool for teaching children and teens the basics of mechanics and electronics. This gearbox is made for educational purposes and hands-on STEM classes.

Summary

A simple one-wheel drive train that is easy to understand for children that are interested in making and robotics. The gear reduction is about 80x, so that a small, 3V toy motor can be used to drive a wheel. The pieces for one side can be printed within one hour on a decently fast machine.

Purpose

The drive unit is designed for mounting on a side of a 4-5mm fiberboard (or other) that is the base board for small two-wheel robot vehicle. Two drive units must be printed for a complete robot. The frame must be mirrored for one of the sides.

Source

Designed in FreeCad, feel free to redesign and optimize.

Assembly and additional Parts

The drive unit needs:

•  2 x 2.5mm polished steel rods as axles. 
  • Wire coat hangers cut to size might work after checking the design. The frame is designed to be a bearing fit for the 2.5mm axles, the gears and pulleys are a push-fit.
• 2 loom bands or small rubber bands as drive belts. 
  • The rubber musn't be too thick, otherwise the belt will run of the pulley. 
• 20x15mm Toy Electric Motor
  • I had motors advertised for 3V which had no torque and way too few windings. I rewound my motors with 120wdg (0.1mm enamel wire) to be reliably powerful enough at <3V.
• Zip-Tie
  • For mounting the motor to the frame
• 2 M3-screws 
  • For mounting the frame to the board. 
• M4-Screw
  • For mounting the wheel. The wheel axle hole is slightly smaller than 4mm, so that a M4-Tap can be used to thread the hole. Not-tapping-through all the way makes the screw a snug fit so that it does not come out by itself.
• Piece of bicycle inner tube
  • As tire. 3D-printed wheels are very slippery, and the tire gives it enough grip.