The only problem I see with this is the moment you introduce another component I.E. a relay into the equation you have one more point of potential failure. Let us assume for a moment that this relay is damaged in combat, or just fails, there is the real possibility of you having the situation where you have a robot with an LED that is on (safe in your eyes) but in reality you have a fully powered up robot on your hands!!! As for relying in a separate supply for said LED...yet again, something else to fail.
Ever heard of K.I.S.S. ?...Keep It Simple Stupid!(no offence intended) All that is required is an LED wired across the side of your removable link that is isolated when the link is removed and 0V. As a back up we use 2 LEDs in parallel, just in case one does fail.
Link in.. circuit closed..LED on, robot live! Link out.. circuit open..LED off, robot dead!
I know this is not the perfect solution and there is still the remote possibility that an incorrect indication could occur but there is a lot less of a chance than by using your idea!
We use this principle on both our heavy and featherweight machines and we have NEVER had a problem in the arena or when submitting the machines for tech. checks either at RW or live events.
In conclusion, the whole point of a visible indication of a powered up machine is exactly that...an INDICATION ONLY! There is no substitute for safe working practice and proper observation of ALL safety procedures when arming / disarming your machine. I wouldnt trust my own, or any of my teams safety solely to an LED, on or off!
Just my two pennies worth!
Geoff,
Team Scorpion,