Polargraph pen plotter (with two ball bearings)

A detailed description of this model can be found in my [pen plotter blog post](https://stefan.wtf/p/penplotter).

📺 [Assemble Video at YouTube](https://youtu.be/nRvZ9aIs4nk)

💾 [Source File at Onshape](https://cad.onshape.com/documents/b317512108e41c84730e790b/w/0a81f0b6f873123403f579aa/e/00f1ccbc018d863cfe88add2?configuration=default&renderMode=0&uiState=67fcdcf98541cb14f63e8f9d)