Following equation shows how the angular speed ωm, applied voltage u and the generated torque τm of a
DC motor are related.
τm =
Kt
R
u −
K2
t
R
ωm
where Kt and R are constants. The mechanical power output of the motor is given by
Pout = τmωm
=
Ktu
R
−
K2
t
R
ωm
ωm
A motor operated with a 9 V supply voltage has a no-load speed of 12000 rpm. It stops rotating when an
external torque of 4.2×10−3 Nm is applied. Calculate its speed and the mechanical power output when a
torque load of 10−3 Nm is applied.
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