Probably the prosthetic hand I printed that you can see if you look under the “Read More” section under “My Typical Day” on my profile page. It’s a great design that when you operate it makes the fingers grip. This can transform someone’s life and all it cost was £3.50 in materials to make. I’ve just printed a second one where the design has been improved, I’m just about to start assembling it.
It’s closely followed by the 3D print I made for Lecture 3 of of this years RI Christmas Lectures – you can read all about that here :