Motor Performance and Characteristic Curves

Vocabulary flashcards covering DC motor specifications, mechanical power, torque-speed relationships, efficiency, gear ratios, and motor performance curves.

Four Primary Motor Specifications

The essential measurements required to characterize a motor at a given voltage: power, efficiency, current, and speed.

No-Load Speed ($\omega_{\text{no-load}}$)

The angular speed at which a motor spins when it is loaded with no external torque ($\tau = 0$).

Stall Torque ($\tau_{\text{stall}}$)

The load torque applied to a motor that causes the motor to stop spinning completely ($\omega = 0$).

Mechanical Power ($P$)

The rate at which work is performed in a given time, calculated as torque multiplied by angular speed ($P = \tau \times \omega$).

Maximum Power Point

The operating point where a motor delivers maximum mechanical output power, occurring at half of the stall torque ($\frac{1}{2}\tau_{\text{stall}}$) and half of the no-load speed ($\frac{1}{2}\omega_{\text{no-load}}$).

Motor Efficiency ($\eta$)

The ratio of mechanical power output ($P_{\text{out}}$) to electrical power input ($P_{\text{in}}$), expressed as a percentage: $\eta = \frac{P_{\text{out}}}{P_{\text{in}}} \times 100\%$

Gear Ratio ($GR$)

The ratio of output torque to input torque in a mechanical gear train system, given by $GR = \frac{\tau_{\text{out}}}{\tau_{\text{in}}}$

Current at Maximum Output Power ($I_{\text{maximum output power}}$)

The operating current halfway between the stall current and the no-load current: $I_{\text{maximum output power}} = \frac{I_{\text{stall}} + I_{\text{no load}}}{2}$

Heat Power Loss Rate ($P_{\text{heat}}$)

The rate at which electrical energy supplied to a motor is transformed into unwanted thermal energy, calculated as $P_{\text{heat}} = (1 - \eta_{\text{max}}) P_{\text{electrical}}$

Motor Characteristic Curves

Graphical curves showing how motor speed, power output, current, and efficiency depend on motor torque at a constant operating voltage.