It would make a cradle with electric method indicated in the figure (the average arc specified transparent convention: for the kind of place position of the spring). Instead of a huge board for mounting the electromagnet and a spring may apply loads, weighing no less tear strength.

In my version of motion parameters cradles regulated: the amplitude of the output voltage of the autotransformer TV1, the frequency - variable capacitor C2. But these options profitable (and waveform) to determine the most optimal and use the cradle without these controls.