We had some of these drop on our desk a while back with a “You gotta find more of these!” message taped to it. What it turned out to be is a pretty cool, inexpensive geared stepper motor, ideal for a bunch of low-torque applications.

This 28BYJ-48 is a 5V unipolar geared stepper motor, manufactured by the boatload for the HVAC control industry, where you’ll find these little units as actuators for airflow control in ducts and vanes. It features a 5mm “Double-D” shaft, mounting lugs, and a nice 5-conductor 0.1″ pitch connector. The gearing isn’t the beefiest or most precise we’ve ever seen, but it’s adequate for reasonable loads.

Being a stepper motor, you’ll need a motor driver circuit. There are many ways to drive a stepper, but this ULN2003 driver board is specifically designed to drive these 5V stepper gear motors.

Specifications:

• 64:1 (63.68395:1) gearing
• Solarbotics Tested
• Torque @5V:
  • FULL Step mode: 821gmf*cm (11.4in*oz) @ 200mA draw
  • HALF Step mode: 598gmf*cm (8.3in*oz) @ 256mA draw
• 2038 steps per revolution
• 4-phase unipolar stepper wiring through 23cm (9″) long cable to 5-pin connector (0.1″ pitch)
• 5V nominal voltage
• ~35 ohms coil resistance
• Basic dimension:
  • 28mm diameter
  • 20mm tall (excluding shaft)
  • 5mm dia. “double-D” shaft, 9mm long
• 37g

Thanks to Graham Wideman for his additional in-depth analysis of these gear motors.