I was playing more with foam board today. I’ve used it before to make drawer dividers, but at 10mm it gets interesting. This is a rough (rabbet I think) joint I made with it, because why not.

I used no measurement, or glue - just cut based on the other part. These were offcuts from a larger robot arena.

Foam board is light, slightly flexible and easy to cut. It could be useful for light mounting on a robot. When learning robotics at home, this material can also be used to make arenas and arena props for the robot to be tested in.