[Rick TYler]

Originally Posted by ErichKeane

Another household device which has the body grounded is your computer case, for the same reasons. Most metal cases are grounded (as are many laptop cases, if not, at least the trays) for these reasons, and the computer manufacturers don't face huge risks from awry wiring! Again, it is to protect the user.

You're confusing 12v apples with 120v oranges. That computer case is grounded, but it's an earth ground to the house. Computer makers also don't run 120 volts through that case. Trust me. I experienced an ethernet error that carried 120 volts to the case of a PC and there was absolutely no doubt what happened. My arm still hurts when I think of it.

There is no way to provide a real earth ground on your moving robot, so that is simply not an issue or a possibility. There is no safety benefit to "grounding" your negative lead to the robot chassis mostly because there is no electrical shock hazard on your 12-volt battery. If you don't believe me, lick your thumb and forefinger and place them on the terminals of your battery. That battery is capable of amazing current flow, but humans have more than enough effective resistance to reduce that the nearly zero with only 12 volts. I still remember the day my friend Ed and I tried this on a car battery (we had both recently earned our Novice Amateur Radio licenses and knew intellectually that 12 volts wouldn't hurt us, but it took a certain amount of nerve to test this knowledge). It was exactly like placing our fingers on block of stone -- we couldn't feel a thing.