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Servo Tester

A dedicated hardware debugging tool that measures servo angle accuracy against a potentiometer reference to catch factory calibration defects.

Project Overview

Cheap hobby servos like the SG90 and MG90 don’t always turn to the exact angle they’re commanded to — a factory defect that throws off kinematics calculations on robots like my Quadruped Spider Robot. This tester measures that error directly: a reference potentiometer sets a target angle, the servo is driven to match it, and a second potentiometer attached to the servo horn reports the actual angle achieved.

Source Code Repository

Technical Details

  • Built around an Arduino Nano with a 128x32 OLED display for live angle readout.
  • Two 10k potentiometers (reference input and servo feedback), a push button, and a 220µF capacitor for power smoothing.
  • 3D-printed attachment jig, glued to the servo horn after zeroing the potentiometer to its default position.
Close-up of the assembled servo tester: Arduino Nano, OLED display, two potentiometers, and a push button on protoboard Schematic of the servo tester: Arduino wired to the OLED, potentiometer, rotary encoder, and servo header

Conclusion

Measuring servo error with a potentiometer is imperfect — the attachment point introduces its own small deviation, and results only hold at constant voltage — but the tool still significantly sped up debugging on the quadruped robot.

References