Ekaggart Singh Kalsi
i built the first doodle clock http://hackaday.com/2012/03/14/robotic-doodle-clock/ 3 years ago as a joke. But to watch the clock work was so mesmerizing that i wanted it to be a practical desk clock. The biggest problem with the first clock was the drying up of the markers after just 30 minutes of working. So the solution to that i found was the magnetic writing boards http://www.walmart.com/ip/Fisher-Price-Doodle-Pro-Basic-Purple/26012794 made for children. I used 2mm cylindrical magnets inside a solenoid to write and erase the text. Next i replaced the servos with small geared steppers to make the clock very silent and smoother. And finally all parts were designed and 3d printed . I also got the final pcb manufactured .The clock uses two 1:100 geared 15mm stepper motors to move the arms configured in a scara fashion. The motors are located at the base to keep the weight very low on the arms. The tip of the arms contains two solenoids with cylindrical magnets inside them. I initially tried electromagnets but to get the text to be as dark as what is written by the magnet which comes along with the board needed a lot of power. The entire clock is run by a atmega 644p with a arduino bootloader. The motors are run by the standard stepstick and the coils are run by a l293dd dual h-bridge. The kinematics for the arm was solved by a user on the reprap forum. http://forums.reprap.org/read.php?185,283327 the only problem that remains is that the board gets scratched only after a day of use. i am looking into covering it with a scratch resistant film or plexiglas.