We're always testing our ideas with physical prototypes so we use digital fabrication equipment to knock out experiments quickly in ways that we can tweak individual variables and track changes. We've got a 20"x12" 60W laser cutter and an Ultimaker 2 in house. We also make liberal use the CNC tools at NYC Resistor, our local hackerspace. Delrin is an excellent material for prototyping rigid mechanisms and flexures on the laser cutter and fabric backed neoprene cuts beautifully for experimenting with garments and medical braces. I also build prototypes in sheet metal and wire and use a homemade spot welder to get them together.