An apparatus has a first truck that includes a frame. A roller is rotatably attached to the frame and a lever arm is pivotably connected to the frame. The lever arm includes a load point, a magnet, and a non-ferrous conductive material. A biasing element biases the lever arm into a first angular position. A load applied to the load point drives the lever arm against a biasing force of the biasing element, and towards a second angular position.