A-axis pulse equivalent calculation

Space Teams CNC
1

A-axis Pulse Equivalent Calculation

User statement

The switches of the A-axis stepper motor driver of the Swift CNC at ASMBLY is set to 1600 stepper microsteps (or pulses) per revolution. One revolution is 360 degrees. The rotary chuck is driven by a 120 tooth belt gear which is directly connected by belt to the stepper motor’s 20 tooth belt gear (the 6:1 ratio is known, but the tooth count might be different). Therefore the pulse equivalent is 26.666666+ for 1 degree of chuck rotation.

Assistant response

Your arithmetic is correct, assuming there is no additional gearing inside the rotary beyond the 120:20 belt ratio.

Work:

  • Driver setting: 1600 pulses per motor revolution
  • Belt ratio: 120 tooth chuck pulley / 20 tooth motor pulley = 6:1
  • So one chuck revolution requires 6 motor revolutions
  • Pulses per chuck revolution = 1600 × 6 = 9600 pulses
  • One chuck revolution = 360°
  • Pulses per degree = 9600 / 360 = 26.6666667 pulses/degree

So the pulse equivalent for chuck rotation is:

26.6666667 pulses per degree

Equivalently:

  • 0.0375° per pulse
  • 9600 pulses per 360° chuck revolution

The only caution is terminology: this is not “1 degree of motor rotation,” it is 1 degree of chuck rotation. If that is what you meant, then yes, your result is right.

User clarification

Yes, I meant 1 degree of chuck rotation. If we write “G1 A1.000” GCODE for the A-axis the Chuck moves 1 degree.

Assistant response

Yes — under that controller configuration, that is the intended meaning.

Given:

  • driver/motion setup = 26.6666667 pulses per degree
  • A axis programmed in degrees of chuck rotation

then:

  • G1 A1.000 means move the A-axis to 1.000° chuck position in absolute mode (G90)
  • or move +1.000° from current position in incremental mode (G91)

Internally, the controller would convert that commanded 1.000° into about:

  • 26.6666667 pulses

Since the hardware can only emit whole pulses, it must quantize/accumulate that somehow, but at the G-code level the meaning is still 1 degree of chuck rotation.

A useful consistency check:

  • G1 A360.000 should produce exactly one full chuck revolution
  • because 360 × 26.6666667 = 9600 pulses

So your interpretation is correct: with that pulse equivalent, A1.000 corresponds to 1 degree of chuck motion, not 1 degree of motor shaft motion.