DC Motor Torque

A DC motor produces torque because current flowing through its armature conductors experiences a magnetic force in the motor’s magnetic field. The torque constant k_t tells you how much turning effect the motor creates per ampere, so for a given motor design the torque rises linearly with current. This relationship is a practical motor model used when the motor is operating in its normal linear range, before saturation, overheating, or other non-ideal effects become significant.

Use this formula when estimating how much twisting force a DC motor can deliver from a known current draw, such as in robotics, actuators, and drive systems. It is also useful when designing current limits or checking whether a motor can meet a torque requirement.

• Using the wrong units for k_t, such as N·m instead of N·m/A
• Confusing current with voltage and plugging in volts for I
• Forgetting that this gives torque only for the ideal linear model, not the exact behavior under all conditions