Lecture Notes: Comparison of MKS Servo 42C Closed Loop Stepper Motor and Other Motors

Introduction

• Purchased MKS Servo 42C closed loop stepper motor from AliExpress.
• Fascination with motors prompted addition to collection.
• Setup was straightforward with connectors, motion control board, and calibration.
• Comparisons with NEMA 17 open loop stepper motor and self-designed servo.

Setup and Calibration

MKS Servo 42C

• Arrived well-packaged.
• Features a small OLED display for navigation.
• Calibration without load recommended; took approximately one minute.

Comparison Motors

• NEMA 17 Open Loop Stepper Motor:
  • Larger size.
  • Driven by TMC 2209 driver.
• Self-designed Servo:
  • Smaller BLDC motor (C3548).
  • Extensive calibration process (six minutes).
  • After calibration, eliminates cogging and stiction.

Thermal Performance

• Comparison during holding position with no load:
  • Servo and Closed Loop Stepper: Minimal current, electronics barely warm.
  • Open Loop Stepper: Draws about 12W, driver heats up significantly.

Performance Testing

Test Setup

• Linear system similar to 3D printer for acceleration and speed tests.
• Components: Linear guide, GT2 belt, optical end stop, accelerometer.
• SKR 1.4 motion control board with Clipper; uses 3200 steps per revolution.
• Tests conducted at 12V and 24V (testing at 24V damaged SKR 1.4).

Testing Process

• Python program for stress testing.
• Home, move, home again to check for skipped steps.
• Binary search to find maximum acceleration and speed.

Test Results

Open Loop Stepper Motor

• Acceleration test: 1000 mm/s² comfortable, maximum acceleration decreases with load.
• Speed test: Fails at higher speeds due to reduced torque.
• Results show potential as a simple, low-cost solution despite power usage.

Servo

• Provides detailed feedback including position error.
• Hits 40,000 mm/s² cap without load.
• Struggles with 500g load due to overshoots; possible tuning issue.
• Faster than stepper in every test.

Closed Loop Stepper

• Quiet operation but limited speed (333 mm/s observed).
• Suspected reporting issues with position error.
• Performance suffers with load; disappointing results in speed and acceleration tests.
• Potential configuration issues.

Conclusion

• Each motor type has strengths and weaknesses:
  • Closed Loop Stepper: Quiet, energy-efficient, suitable for specific applications like camera dollies.
  • Servo: Best for speed and acceleration if control loops are well-tuned.
  • Open Loop Stepper: Good low-cost option despite power inefficiency.
• Future potential for further testing and applications.