On the subject of weight being off--the other thing whole robot models ignore, besides nuts and bolts, is wiring, and sometimes pneumatics as well. (I have never been able to find a CAD model for a compressor.) 6 gauge wire is heavy, and smaller gauge adds up. Also, nuts and bolts are steel, which is more than 3x as dense as aluminum. (.30 lbs/in^3 vs. .098 lbs/in^3 Rachel knows these numbers by now
) We took off a handful (literally, I held them, maybe 10?) of bolts and t-nuts, that we had added as spares in our 80-20, and I would estimate it lost us a pound.
The most accurate way I found was to just weigh the base in real life, and assume that weight for that assembly. All other assemblies were a lot closer to reality.