Anorher means of knowing bit has hit board with motor not runing would see a tilt in the sled angle. Accerleratoon miight be more difficalt to detect as leadscrew gives stepper motor a gear reduction. Conductive probably most accurate. Bit could dent into wood befote tilting sled. Current detection enteresting idea that might detect but probably would need multiple tries up and down to find z azis home. EMI is difficult to remove. Even steel may not block. What shield rooms require with constant monitoring is exceptional. I had thought that if needed maybe using copper tape for shielding might help but unlikely. I am questioning drivers ability to detect stepper motor current as someone has reported just one z axis motor runming. That should not be possible per Bar.
Martha