DC motors worksheet with answers

Free printable DC motors worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy
+−120 VRa​Ia​ = 6 AM+−EωT = ?

A permanent-magnet DC motor has the torque constant k = 0.08 N·m/A. Find the torque T it develops at an armature current of 6 A.

k = 0.08 N·m/AIa = 6 A
T = N·m
2.Easy
+−120 VRa​Ia​ = 15 AM+−EωT = ?

A permanent-magnet DC motor has the torque constant k = 1.5 N·m/A. Find the torque T it develops at an armature current of 15 A.

k = 1.5 N·m/AIa = 15 A
T = N·m
3.Medium
T (N·m)n (rpm)Tst​ = ?n0​

A DC motor with k = 0.6 N·m/A and Ra = 0.2 Ω is connected to 220 V. Find its stall torque Tstall, the torque at zero speed.

V = 220 Vk = 0.6 N·m/ARa = 0.2 Ω
Tstall = N·m
4.Medium
T (N·m)n (rpm)4 N·mn0​n = ?

A DC motor (k = 0.8 N·m/A, Ra = 0.8 Ω) runs from 110 V and drives a load torque of 4 N·m. Find its speed n in rpm.

V = 110 Vk = 0.8 N·m/ARa = 0.8 ΩT = 4 N·m
n = rpm
5.Hard
T (N·m)n (rpm)4 N·m750 rpm

A DC motor with k = 1 V·s/rad and Ra = 1 Ω must drive a load of 4 N·m at 750 rpm. Find the armature voltage V it needs.

k = 1 V·s/radRa = 1 ΩT = 4 N·mn = 750 rpm
V = V
6.Hard
+−110 VRa​ = 1.5 ΩM+−EωT

A small DC motor has an armature resistance of 1.5 Ω and runs from 110 V. Neglecting rotational losses, find the largest mechanical power Pmax it can develop at any speed.

V = 110 VRa = 1.5 Ω
Pmax = W

Answer key

  1. 1. T = 0.48 N·m
  2. 2. T = 22.5 N·m
  3. 3. Tstall = 660 N·m
  4. 4. n = 1265 rpm
  5. 5. V = 82.54 V
  6. 6. Pmax = 2017 W

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