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
+−220 VRa​Ia​ = 12 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 12 A.

k = 0.08 N·m/AIa = 12 A
T = N·m
2.Easy
+−24 VRa​ = 0.5 ΩIa​ = 2 AM+−EωT

A DC motor runs from 24 V with an armature current of 2 A. The armature resistance is 0.5 Ω. Find the developed (electromagnetic) power Pdev.

V = 24 VIa = 2 ARa = 0.5 Ω
Pdev = W
3.Medium
+−VRa​M+−En = 1200 rpmT = ?

A DC motor delivers 15 kW of mechanical power at 1200 rpm. Find the shaft torque T.

P = 15 kWn = 1200 rpm
T = N·m
4.Medium
T (N·m)n (rpm)0.2 N·mn0​nFL​

A DC motor (k = 0.1 V·s/rad, Ra = 1 Ω) runs from 24 V. At full load it draws 2 A. Neglecting the no-load current, find its speed regulation SR = (n₀ − nFL)/nFL in percent.

V = 24 Vk = 0.1 V·s/radRa = 1 ΩIFL = 2 A
SR = %
5.Hard
T (N·m)n (rpm)7.2 N·m400 rpm

A DC motor with k = 0.6 V·s/rad and Ra = 0.4 Ω must drive a load of 7.2 N·m at 400 rpm. Find the armature voltage V it needs.

k = 0.6 V·s/radRa = 0.4 ΩT = 7.2 N·mn = 400 rpm
V = V
6.Hard
+−48 VRa​ = 2 ΩM+−EωT

A small DC motor has an armature resistance of 2 Ω and runs from 48 V. Neglecting rotational losses, find the largest mechanical power Pmax it can develop at any speed.

V = 48 VRa = 2 Ω
Pmax = W

Answer key

  1. 1. T = 0.96 N·m
  2. 2. Pdev = 46 W
  3. 3. T = 119.4 N·m
  4. 4. SR = 9.091 %
  5. 5. V = 29.93 V
  6. 6. Pmax = 288 W

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