Cheap Powerful Electric Gearmotors

Bought 2 powerful motors for a mini sumo from Ebay for $11 each.


  • Static Torque: 1.5 N*cm
  • Voltage: 12V DC
  • RPM: 1000RPM
  • Diameter: 25mm
  • Length: 52mm
  • Shaft diameter: 4mm (D-profile)
  • Weight: 76g
Measured parameters:
  • Inductance: 0.9 mH
  • Resistance: 2.5~3 Ohm
  • BEMF or Torque constant: 0.112
  • Inertia: 1.071e-4 kg*m^2
  • No-load Current: 0.11 A at 12V
  • No-load Torque: 1.232 N*cm
  • Electromagnetic time constant: 0.36 ms
  • Mechanical time constant: 21.34 ms
By connecting a signal generator to a motor with a resistor in series to measure current with an oscilloscope.

Image from DSO203

Measure Time Constant of a dynamic process and multiply it with Full active resistance in series, to find out the Inductance.

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