Technology and Engineering · High school

Brushed DC motor

Set the voltage and the brake; in slow motion, watch the commutator reverse the current every half turn.

In the learning section below the figure, predict, try, complete the tasks and check yourself with short questions.

Fig. 1Brushed DC motor

Slide the voltage and the brake; look inside with the cutaway or take the motor apart

Parts and inside

Separation0%

With the motor apart, hover over a part, tap it or pick it from the list.

Pick a part to see what it does and what it is made of in a real motor.

Speed: 0 rpm
Current: 0.00 A
Torque: 0 mN·m
Back EMF: 0.0 V

Voltage0.0 VBrake (load torque)0 mN·m

Your own values

Type in the voltage, the load and the motor’s two constants yourself; values beyond the sliders work too. Use a comma or a point for decimals.

Voltage

Load

Winding resistance R

Motor constant k

At this voltage this motor runs at about 0 rpm with no load; at start-up it draws 0.00 A and gives 0 mN·m of torque.

No voltage: no current flows in the coil, so there is no force.

Learn

Progress is kept on this page only; no points are given.

1Predict
2Try
3Explain

With the motor running at 12 V, what happens to the current it draws if you tighten the brake?

Purple arrow: force on a side of the coil (its length is proportional to the current)Gold half ring: the commutator segment touching the positive brushWhite dots: direction of the current in the coilThe numbers come from a simple DC motor model: V = I·R + k·ω and T = k·I. Example motor: winding resistance R = 2 Ω, motor constant k = 0.02 V·s/rad, bearing friction 2 mN·m. At 12 V it runs at about 5600 rpm with no load and draws 6 A when starting. The coil in the drawing turns at about one sixtieth of the real speed (one six-hundredth in slow motion; for very fast motors you enter yourself the drawing turns at a capped speed), and the speed-up is slowed down too so you can follow it. If you enter your own values, every number is worked out from them with the same equations. Real motors have many coils and segments to smooth out the torque.

How does an electric motor turn? Inside a brushed DC motorRead the article