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Electric Motor Specifications

Jun 20, 2017

Take a good look at the motor specifications.

Before choosing a motor, you should look at least three primary specifications:

  • Motor type: electrical motors can be divided in different criteria including here the cheapest motors or how simple is to work with it. In every aspect, the DC motors wins and there are very high chances to find the desired electric motor that can fit in your robot;

  • Electrical characteristics: before planning what battery packs will be used in the project, you have to find the nominal voltage where the motor runs, and the values for stall and rated currents. Most DC motors can run in the 12-24V range, while the stall currents can vary from a 1-2 amps to over 30 amps;

  • Mechanical characteristics: these characteristics include details about the stall torque of the motor, rated torque, no-load speed of the motor, and other mechanical characteristics. Most of DC electrical motors can reach between ~5000 rpm and up to ~20000 rpm, and have a linear torque to speed ratio;

Some additional further considerations

  • the speed of the motor is solely dependent on the voltage applied to the motor for a given load, and regardless of speed, a constant current applied to a DC motor produce a constant output torque;

  • a general rule for DC motor related to the most efficient area of operation is to operate the motor at approximately 70% to 90% of its no-load speed and from 10% to 30% of its stall torque;

  • the power of a motor is the product of speed and torque, while the maximum power of a DC motor can be achieved at the operating point that is defined by operation at half the no-load speed and half the stall torque;

  • depending on additional factors such as environmental conditions or weight, the speed and torque produced at a constant voltage are inversely related. This is the case when the motor produces a higher torque at a lower speed;

  • to have a lower noise when the motor is used with gearing and in the same time save the battery life, the motor should be selected for the minimum speed practical by choosing a motor with higher voltage ratings than the available voltage supply;