Speed of a Cumulative Compound DC Motor

[mobin.abrar]

I came across an equation for the Speed ω in Radians/seconds of a Cumulative Compound DC motor.

ω= K(V_t-I_A[R_A+R_F)/($\Phi$_P+$\Phi$_S)

• How would we calculate K in this equation?
• Shouldn't the Terminal Voltage Vt be replaced by Armature Voltage Ea?
• I came across a lot of varying torque speed curves. WIll the curve be exponentially decaying or linear?

 

[mfb]

Maybe you should explain your formula and the used variables, or at least give its source.
My guess: K is some constant given by the geometry of the motor.

I came across a lot of varying torque speed curves. WIll the curve be exponentially decaying or linear?

I don't think that any of these curves are perfectly exponentially or linear. In addition, it might depend on the motor (e.g. how its internal friction depends on the angular velocity).