Induction motors
The rugged, magnet-free alternative that Tesla popularised for rear axles.
- Explain induction motors at engineering level
- Read the numbers that define the behaviour
- Apply the idea to a real drive unit
Overview
Induction motors generate rotor current entirely by electromagnetic induction from the stator field, needing no magnets and no direct electrical connection to the rotor at all.
In depth
An induction motor's rotor is typically a 'squirrel cage' — aluminium or copper bars short-circuited by end rings. The stator's rotating field induces currents in these bars, and those currents produce their own field that interacts with the stator field to create torque — but only if the rotor spins slightly slower than the field, a difference called slip.
Slip is the fractional speed difference between the synchronous field speed and the actual rotor speed; typically 1-5% at rated load.
- NoneMagnetsRare-earth magnets
- LowerPeak efficiencyHigher
- NoneCost sensitivity to magnet priceHigh
- ExcellentFree-spin (no drag) capabilityRequires disconnect
- LowerTorque densityHigher
Key takeaways
- Induction motors generate rotor current purely by induction, with no magnets needed.
- Slip — the small speed lag between rotor and field — is fundamental to how they generate torque.
- They trade some efficiency and torque density for lower cost and true zero-drag freewheeling.
Confirm you've read through and we'll count it toward your progress.