Improved printable eggbot

Eggbot in action: http://youtu.be/w5YWRMa1uJk. Make your own and have fun designing and plotting your own designs onto eggs, balls or light bulbs.

Remixed from earlier designs, I have added some improvements of my own as follows:

End plates have been changed to allow more pen travel. The top front hole for an M8 stud on the original design was redundant because an M8 stud fitted there would interfere with the pen when lifted. The height of the end plates also limited the possible pen travel left and right. It would be possible to reduce the overall height of the end plates to 75mm and correspondingly reduce the height of the back plate by 25mm, but I chose not to do this because the back plate offers some useful protection to the pen arm when not in use. It also makes for more vertical space to mount the electronics. I added angle brackets to either side at the front to take the flex out of the end plates and therefore better hold the axes of the drive shaft and idler shaft