Technology
Linear induction motors
Contactless thrust for transit, launch and industrial motion. Choose the motor layout, reaction plate and mounting arrangement around your duty.
How a LIM works
A powered primary creates a travelling magnetic field. This induces currents in a conductive reaction plate; their interaction produces thrust across an air gap. Think of a rotary induction motor unrolled into a straight line.
During motoring, the field moves faster than the plate. This speed difference—slip—affects thrust, current and plate heating. Gap, plate material and operating speed also matter.
Thrust does not depend on wheel–rail grip. Gradients still add load, and the running gap and environmental conditions remain design inputs.
Diagram: a rotary motor unrolled
Illustration · not to scale. Scroll sideways if needed.
Illustration only; the rotation-to-linear sequence explains the principle.
Single- or double-sided?
| Design choice | Single-sided (SSLIM) | Double-sided (DSLIM) |
|---|---|---|
| Arrangement | One primary faces a conductive plate, usually backed by steel. | Two primaries face a bare aluminium or copper fin. |
| Mechanical loads | The structure and bearings must carry the normal magnetic pull. | Symmetry can balance normal forces on the fin; the frame still carries magnetic loads. |
| Choice | One active face and no second-primary frame. | Two active faces can provide more thrust within a given track width; centring and support matter. |
Diagram: single- and double-sided construction
Illustration · not to scale. Scroll sideways if needed.
One active primary, a single-sided steel-backed plate, then two primaries around a bare fin.
Where the primary sits
| Design choice | Primary on the vehicle | Primary in the track |
|---|---|---|
| Moving hardware | Powered primary on each vehicle. | Passive reaction plate on each vehicle. |
| Track hardware | Passive reaction rail along the powered route. | Primaries and power connections in the active zones. |
| Trade-off | Motor count follows fleet size; reaction-rail cost follows route length. | Lighter vehicles; more track-mounted motors and sectional control. |
Diagram: a track-mounted motor driving a vehicle
Illustration · not to scale. Scroll sideways if needed.
A powered primary acts on the reaction plate carried by the vehicle.
Diagram: propulsion viewed from above
Illustration · not to scale. Scroll sideways if needed.
Plan view of the reaction plate crossing powered motor sections.
Plate choice and sizing
Aluminium is a common starting point where moving mass matters; copper is another option. Higher conductivity is not automatically better: plate material and thickness must suit the slip and speed range.
- Duty: mass, thrust, acceleration, target speed, route, gradients, stops and cycle time.
- Installation: available space, mounting, running gap and any existing plate or rail.
- Limits: supply, temperature, weight and cost.
Axis provides motor sizing, performance predictions and drive requirements, supported by circuit models, finite-element analysis (FEA), route and thermal simulation. See our design service for the deliverables and checks.
Have a motor duty in mind?
Send the load, speed, route and available space.