Yes, you will need a sensor to determine the speed of the rotation. For instance, you can use a hall effect sensor and put a magnet on the shaft of rotation. By installing the hall effect sensor near the shaft that contains the magnet, you can use this to determine the RPM of the axis and reflect this value in Mach3 using an input in your controller and setting that input in the index line item of the Mach3 input signals dialog box.
Here is a great video that shows the circuit and process:
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You can set the Index input with Mach3 Turn and check that the Index is lit on the screen, but it is not reflected in the rotation speed. Is there any way?