Sketch the root locus of the armature-controlled dc motor model in terms of the damping constant c,

Question:

Sketch the root locus of the armature-controlled dc motor model in terms of the damping constant c, and evaluate the effect on the motor time constant. The characteristic equation is
LaIs2 + (RaI + cLa)s + cRa + KhKT = 0
Use the following parameter values:
Kb = KT = 0.1 N · m/A I = 12 × 10-5 kg · m2
Ra = 2Ω La = 3 × 10-3 H