How they built them

[deathproof]

I may have asked this before, but are there any resources regarding how the droids from the OT were built?


There are bits pieces here and there... we know IG-88's head was from a specific jet engine. The eye pieces for WED-15 are from a 70's slide projector.

But how did the droid builders come up with the R2 and R5 heads? Or their bodies? Did they use existing pieces from something or were they built from scratch? What about the Probe Droid or Death Star Droid? Star Wars was on a tighter budget so you'd think they would use as many existing parts as possible to negate the need to custom build anything.