I am not saying safety is not VERY important.
Good - we agree!
I am just saying a heartbeat monitor is guaranteed not the way to implement it.
It is not the normal way to monitor safety and is plain inaccurate.
Set too low and the excitement of trying it shuts it off immediately, set too high and its useless.
Something that I didn't make clear in my post was that the suggestion of "heartbeat monitoring" was something to be investigated (along with the other items), not that it was necessarily needed; only the designer/builder could determine that. If the OP were only using a single controller (aka Arduino), then it wouldn't help. If, however, multiple controllers were used (say separate ones to monitor/control steering and other functions), then some form of "heartbeat" or check between the controllers could help to determine if one or more have failed, and if so, activate the "full-emergency-stop" functionality.
FWIW, You should have a LARGE relay on the main power to the motors and in case the safety system is triggered, it will kill all motor power even in the event of the relay or mosfet controlling the motors short.
That's a good idea; ultimately it will be up to the OP to determine how far to take the safety system, depending on where and how the device is planned to be used (and the level of supervision given to it).
