I have access to (not quite working) 3D printer. It has no endstops, no switches that would detect extreme positions of head or table. I know this because I was there when it was assembled. All cables are accounted for. 4 for each Nema 17 step motor, 2 x 2 for thermistors, 6 x 2 for heaters and that's all.
Yet, despite the lack of any sensors, printer can move head to extreme right or left, can move table to the bottom or to the top and so on. And motors don't get hot. It just goes to the end and then moves back a fraction of millimeter and stops.
So, how could they do it? What's the "signal" of end of possible movement, when all we got to work with is 4 cables that power said motor? Of course in my projects I plan to use proper endstops, but in case they fail, this would be a welcomed backup mechanism.
To clarify: When we first assembled this thing, it didn't crash to the side, and head was at pretty random position then. Or even if it was a crash, printer apparently somehow got to know about it, because now it has no problems with positioning.