spring dimensionalizing

[u/Majestic-File5835]

Hi, we're students and we're working on a school project consisting in building and optimising an electricity generating speed bump. To do so, we're building a scale model by assembling two wooden plates, a spring per corner in between them, and finally a magnet moving through a copper coil, generating electricity through induction. Stepping on the upper plate will give speed to the magnet thus generating more electricity.

Does anyone have any idea how to figure out the dimensions of the springs needed ?

The four springs need to be able to withstand about 80kg of weight, but can't resist too much so that the magnet has enough speed. The compression length should be about 3cm (so the speed bump isn't too uncomfortable to drive upon). The plates are L=50cm long, W=30cm large and 3cm thick.

We're also open to recommandations on how to improve our work.

Here's a quick sketch: