# Mini-Mapper 6: Motor encoder mechanical design

Before looking at the circuitry needed for the motor encoder, we need to think about the mechanical interface between the motor, motor encoder and the motor prototype PCB.

The idea is to have an encoder disk attached to the motor output that passes through the gap of a photointerrupter (an infra-red LED and a phototransistor in a shared package with a slot in it), and for the photointerrupter to be mounted on the PCB, with the PCB being attached to the robot chassis. Getting all that to work nicely requires a little bit of mechanical design, which is what this video is about!

• The project repository is at tag episode-006 for this video.
• I'm using FreeCAD for the mechanical modelling, because it's awesome and free.
• The mechanical models are in the mech directory of the repository, but here's a PDF document with some views of the models so you don't need to set up FreeCAD.