With a DVM, fluorescent lighting, and a bi-color disc on the armature shaft, you can measure the motors RPM.
Painting ¼ of the tires side wall white you can measure the RPM of the rear wheels.
To measure the wheel or motor’s RPM, start the motor slowly and watch the movement of the pattern on the side wall or disc, the first time that it stops is at 3600RPM, the second time is 7200RPM.
Take either 3600 or 7200 and divide it by the Voltage read on the DVM at those speeds and multiply it by 12 to get the RPM at 12Volts.
Example;
Rear Wheel RPM3600 @ 4.51 Volts.
3600 divided by 4.51, times 12, equals 9578 RPM, times 3.11, equals 29789 motor RPM at 12 Volts.
Motor RPM 7200 @ 2.89 Volts
7200 divided by 2.89, times 12,equals 29896 RPM at 12 Volts.
This method isn’t perfect, but it will give you an idea of the wheel and motor RPM.
Free Tachometer
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