Stator and rotor at a glance
The two halves of every rotating electric machine, and how they interact.
- Explain stator and rotor at a glance at engineering level
- Read the numbers that define the behaviour
- Apply the idea to a real drive unit
Overview
Every rotating electric machine, from a toy motor to a 300 kW traction motor, is built from the same two halves: a fixed stator and a rotating rotor separated by a thin air gap.
In depth
Two halves, one air gap
The stator is bolted to the housing and carries the windings that create a moving magnetic field. The rotor sits inside it, connected to the output shaft, and follows that moving field around. The air gap between them is only a fraction of a millimetre to a few millimetres — small enough to keep the magnetic coupling strong, large enough to tolerate manufacturing tolerance and thermal expansion.
Stator and rotor in cross section
Switch to the cross-section view to see how thin the air gap really is.
When learning a new motor topology, first ask: which part carries the controlled current (usually the stator), and which part just responds to the resulting field (usually the rotor)?
Key takeaways
- The stator is fixed and generates the moving magnetic field.
- The rotor turns with the field and is coupled to the output shaft.
- The air gap is a critical, tightly controlled dimension.
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