should start by saying that about 10 years ago I produced some 7mm kits for both a P4 and a P5 coal hopper and R2 and R4 coke hoppers. These were resin with brass strapping over layed onto them. With the moulds dying last year I decided to see if I could upgrade them to be a one piece 3D print.
This was achieved pretty quickly. But then I had the idea to make them work ie make the bottom doors open and close automatically. Easier said than done.
So starting with the P5 hopper this is how far
