I’m sorry if this is buried in there somewhere, but I haven’t put one of these together yet…
Is there an “e-Stop”, or a place to wire one in? Somewhere to centrally kill power to the motors at least. I guess I could plug everything into a centrally switched plug so that one switch kills the router and all (that would probably be safest), but given beta code (and even production code) can do “odd things” sometimes, would like a quick kill method…
Thoughts?
Good point. I have the power for the router and the power for motorshield / motors on a cord with a switch, now placed on the table next to the laptop. One day, on a final frame, I will let that cable run through one or more E-Stops. Thinking of three buttons mounted to 1x2 running over the floor under the frame, so from any position I can just kick it. https://github.com/MaslowCNC/Mechanics/wiki/Safety-First
If you kill the AC power it’ll take a bit of time for the DC to drop, hard to say what it’ll do to the motor controllers if you abruptly cut the DC. At least with Printrboards cutting power while running can occasionally scramble the firmware and/or blow the (quite different from the Maslow) controller chips. The router has the most potential for causing injury and damage; I found a comment on Instructables that shorting a universal motor’s power input will act as a brake but don’t know how accurate that really is.
Some CNC controllers (like the Gecko G540) implement estop in the controller. Smack the big red switch and everything quits moving, although I don’t recall if it also killed the SSR driven through the G540 spindle,
There’s an open github issue for estop support.
I set things up so that killing the 12volt power to the motors will stop them immediately and safely without affecting the controller at all so the USB connection and the machine’s position won’t be lost.
@mooselake is right that we do have the ability to actively brake the motors by shorting their terminals. This feature is not used by the firmware right now, but might be in the future. Because of the reduction gear system even though the motor doesn’t come to an immediate halt when power is cut, the sprocket will only move a tiny amount once power is cut.
Think you could repeat that in front of my (formerly) teenage daughters 
Can the back EMF from the motors damage the controller chips when you abruptly cut power?
Happily! Maybe we could make an animated gif that just repeats 
The back EMF is a great question. Yes, it could damage the controller, but we put in protection diodes for exactly this situation so any back EMF is shorted to ground 
An important point!
I can report so far, that I have used that switch at least 5 times in the past 4 moths and so far nothing was fried. Even then, I’d rather have the mega or the shield going up in smoke, then have the sled been torn apart and a tool with a cutting bit swinging through the room and into my AC or the window.