Instead of building complex machines that might need a size 6 left hand widget with a cross-thread to be kept in the spares warehouse, my philosophy is the opposite.

Build everything out of clunky interchangeable parts - as few as possible. Just like a simple Meccano set. The products are ugly, but functional, and if you bend a leg, you can replace it with an arm. If you burn out a shovel moter you can replace it with an aerial-steering one.

This gives us a need for manned missions to redesign and rebuild the robots (or at least that's my excuse for spending years as a kid building meccano and lego - I was training for a career in space).