How a brushed DC motor turns

Current flows through brushes into a spinning coil called the armature, and the permanent magnets push on that current to make torque. A split ring called the commutator flips the current every half turn so the push always goes the same way. As the armature speeds up it acts like a generator, making a back voltage that limits the current, so the motor settles where that back voltage nearly matches the supply.

Controls

Labels

Animation speed

Supply voltage

Load torque on the shaft

Step through it

Permanent magnetsTwo magnets on the housing wall make a steady field straight across the armature, shown by the faint cyan lines.
Force on the windingsCurrent in the copper windings crosses that field, so each wire feels a sideways push. Pushes on opposite sides of the core add up to a turning torque.
Commutator and brushesFixed carbon brushes rub on a split copper ring. Every half turn the ring swaps which coil ends touch which brush, flipping the current so the torque keeps pointing the same way.
Back EMF sets the speedA spinning coil in a field also generates voltage. With no load the motor speeds up until that back voltage nearly cancels the supply, so only a little current flows.
Adding loadPush harder on the shaft and the motor slows. Lower back EMF lets more current flow, which makes the extra torque the load demands.

The simple motor equations

Torque is proportional to current: T = k x I. Back EMF is proportional to speed: E = k x speed. The supply must cover both the back EMF and the resistance loss, so V = E + I x R, which gives speed = (V minus I x R) / k.

This teaching model uses a small hobby motor with k = 0.02 volt seconds per radian, an armature resistance of 1 ohm and 0.1 amp of friction current. The spin in the scene is slowed down about fifty times so you can follow it.

Try it: set the load to zero and slide the voltage from 3 to 24 volts. Speed rises almost in step with voltage while current barely changes. Then hold the voltage and raise the load, and watch speed fall as current climbs.

Why stalled motors get hot

If the shaft is held still there is no back EMF at all, so current is limited only by the winding resistance. That stall current can be many times the running current, which is why a jammed motor overheats quickly.

Sources

Brushed DC MotorsClemson University Vehicular Electronics Laboratory
Back EMF in a DC motor (lecture demonstration)UC Santa Barbara Physics
DOE Fundamentals Handbook: Electrical Science, Volume 2 (DC motor theory)U.S. DOE Office of Scientific and Technical Information

How to cite this model

Avid Solutions International. (2026, November 11). How a brushed DC motor turns [Interactive 3D model]. Avid Field Lab. https://avidsolutionsintl.com/explore/dc-motor

Last updated November 11, 2026

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