Cool idea -- I remember having a vibrating pen when I was a little kid. I spent many hours drawing sketches with wavy lines! Beyond getting the basic mechanism working, it would be interesting to consider the physical form of the pencil. E.g., how could you attach the motor and the pencil lead so that it's intuitive to hold and easy to manipulate? What constraints does the large motor size provide? Can you work with them, or would a smaller motor be better?