Eddy Current Brake for Vernier DTS Carts

An eddy current brake is a non-contact braking system, most commonly used in trains and roller coasters. In an eddy current brake, magnets are used to induce eddy currents in a metal rotor or other metal part of the vehicle. According to Lenz’s Law, those induced currents create a magnetic field opposing the original field. The two opposing magnetic fields work to slow the vehicle, rather than applying a frictional force like a traditional braking system.

Chris Gaffney and Adam Catching’s article “Magnetic Viscous Drag for Friction Labs” in the Sept. 2016 edition of The Physics Teacher describes their investigation into eddy current braking. As an alternative to a traditional friction lab, their students slid magnets down a long aluminum ramp, slowed by the eddy currents they induced in the ramp.

As a company that sells a lot of aluminum tracks and magnets, it seemed natural to try it out ourselves. We designed and 3D-printed a simple magnet holder for our DTS carts. It holds up to 4 magnets about 2 mm off the surface of the dynamics track.

The attached graph shows the velocity of a DTS cart rolling on an inclined track, with either the eddy current brake (zero, two, or four magnets) or our Friction Pad installed. With zero magnets, the cart’s velocity increases linearly, as expected. With the Friction Pad installed on the cart, the velocity curve is similarly linear, albeit with a shallower slope.

The shape of the velocity curve differs when the eddy current brake is installed. As expected, the induced drag on the cart increases with the number of magnets installed. It is also apparent that the nature of the eddy current braking force is different than simple kinetic friction. For example, it appears that with four magnets installed, the cart reaches a terminal velocity in the four seconds shown.

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