To begin the project, you'll first need to build a robot arm to do the drawing. There are several robotic arms, which are available at many online electronics outlets and eBay, that would do well for this application. A less expensive approach would be to use a set of servo brackets and construct your robotic arm. The following is an image of this arm:
To construct this arm, you can purchase a set of servo brackets on eBay or look for a kit that uses a six degrees of freedom (DOF) mechanical robotic arm at any one of the several online electronics retailers. You can either build the kit or an arm of your own design. Remember to make sure that you get servos with enough torque. For the upper end of the arm, almost any servo will do. For the servo attached at the base and up the chain, you'll need servos with fairly significant torque capabilities. I like to use the HS-645MG servos by Hitec for this application, they have metal internal...