When building a Lost in Space robot, more time is spent planning, deducing, and making detailed observations about the original robot costume in all its versions than is actually spent cutting, drilling, sanding, wiring, and painting. Thankfully, as a third-generation B9 robot builder, I have greatly and gratefully profited from the hard work and dedication of the previous generations of robot builders who have so generously and freely shared their findings with the rest of the B9 building world.
The Lost in Space robot was a very complicated and multifaceted creation. It is difficult for any one builder to know everything about every part of the robot. The greatest obstacle to complete knowledge about the original robot is that it no longer exists  (For the complete and tragic history of the robot, please read the excellent account at Daniel Monroe's Magnetic Lock website).  The original studio blueprints exist and are available, but the prop builders at Twentieth Century Fox greatly deviated from the blueprints when they first began construction of the robot in the spring of 1965.  Consequently, the blueprints are interesting curiosities of little practical value for the robot builder. This facts make Dave Painter's amazing new robot blueprints all the more remarkable. No robot builder can dispense with these. Still, like all blueprints, they do not convey information about the minor details that haunt the B9 builder.

Without the original robot before us to measure, calibrate, and slavishly copy, nearly all of the successes gained by the B9 robot building guild have been made through deduction and second-hand observations and tenuous reverse engineering from original publicity photographs dating from 1965 to 1968, from careful and repeated viewings of episodes of Lost in Space, and from screen grabs made from these episodes.

The following are a few observations I have made from original press photographs. I am unlikely to be the first builder to notice these details, and in many cases, I am merely replicating the conclusions gained from discussions with robot builders far more informed than I. Nevertheless, it may be useful to give these observations an additional public forum for the benefit of the novice robot builder.