Double-Sided Linear Induction Motors (DSLIM)

Why double-sided

A DSLIM places two primary windings, one either side of a thin aluminium or copper reaction fin, and energises them so their travelling fields work the plate together. Because both active faces push the same fin, a DSLIM can approach twice the thrust of a single active face for a given track width, under comparable current, air-gap and thermal limits. That makes it a natural choice where thrust per unit of track width matters and where the reaction member needs to stay light and simple.

Normal-force cancellation in the frame

A single-sided motor pulls hard toward the steel back-iron behind its reaction plate, and that normal attraction is often larger than the useful thrust. In a double-sided motor the two primaries sit on opposite faces of the fin, so their normal pulls act against each other and largely cancel within the motor frame. The result is that the mounting and bearings see mostly the useful thrust rather than a large one-sided attraction, which typically simplifies the mechanical support and the guidance system.

Thrust density and active-face area

With two working faces sharing one fin, a DSLIM concentrates more thrust into a given track length and width than a comparable single-sided layout. Thrust still comes from air-gap power divided by the field speed, refined for the longitudinal end-effect and transverse edge-effect that every finite linear motor carries, so the design work is in getting real usable force from that doubled active area rather than assuming it arrives for free. We size the geometry, winding and drive to hold that thrust across the required speed range and duty, then confirm it in simulation.

Gap tolerance and packaging

A double-sided motor splits its total working gap across two faces, and the fin has to run between the two primaries, so the mechanical alignment and the available packaging space drive the design as much as the electromagnetics do. Tighter gaps generally lift performance but demand more of the guidance and tolerances, so the sensible envelope is set by how accurately the fin can be held centred over the full route. We treat gap, alignment and packaging together, and check the chosen envelope against the thermal and structural limits before committing to metal.

The bare aluminium or copper fin (no back-iron)

Because the field is supplied from both sides, a DSLIM needs no steel back-iron behind the reaction member; the track member can be a plain aluminium or copper fin. That makes the passive part light, low-cost and simple to install over long distances, which is attractive where the whole active length has to be built into the route. The trade-offs, principally the fin material and thickness, the two-sided alignment and the added track structure, are ones we weigh explicitly against a single-sided arrangement for each application.

Applications

The double-sided configuration suits duties that want high thrust density along a light, continuous track, and where adhesion-independent drive matters because rain, ice or gradients would otherwise limit a friction drive. Typical fits include people-movers and transit, launch systems such as roller-coasters and test sleds, maglev propulsion, and industrial and material-handling lines. We size each one with equivalent-circuit models, cross-check with FEA, run the full route and duty in simulation, and confirm the thermal limits before any metal is cut.

• People-movers and transit where thrust per unit track width and a light passive rail both matter.
• Launch systems, including coaster and test-sled propulsion, needing repeatable high thrust.
• Maglev propulsion, drawing on the same travelling-field principle.
• Industrial and material handling over long, continuous active lengths.

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