On Nov 27, 12:33*pm, "Bill Noble" wrote:
"Jim Wilkins" wrote in message
....

beware - this logic would probably be implemented via software, and as one
who has in the past worked with safety critical systems, a software lockup
is one thing to suspect - from a safety design point of view, an override
that requries no software of any kind, and operates through separate wires
and switches is needed.-

The connection between the batteries, drive bridge and motors needs to
be short and as low in resistance as reasonably possible. The
components you might use to break that connection have their own
failure modes, FETs can short and mechanical relays contacts can weld
closed, mercury relays are TOO DANGEROUS FOR OUR CHILDREN. I'ved
worked on designs that had an SCR across the load to blow ("crowbar")
the main fuse, but that solution isn't perfect either. Even a big
knife switch can weld and stick. I'm told the electric motor control
panel on an old Diesel sub was a dangerous duty station.

jsw