We used a very simple design. We are using 4 solid state 12V DC relays for our four drive motors. We connect the power to the relays to the output from the fuse panel to the Victors controlling the motors. When the Victors lose power the relay trips a digital input. We have four LED's on the
operator interface to show when the motors are tripped. The base driver also has special glasses with LED's in the side to show them the same thing. That way the driver knows when to let off and the arm driver can hit em if he doesn't slow down. Redundency is good.