This robotic arm writes the time on a Magna Doodle

Clock a Doodle doo!

Ah, the good ol’ Magna Doodle. For kids, it’s a neat toy. For parents, it’s a chalkboard without the mess. For Makers, well, it’s an innovative canvas to keep track of their day.

The idea to devise a mechanism that can write the time in pen or marker isn’t all that new. Not only isn’t it innovative, it is only a temporary solution as pens run out of ink and markers dry up. Inspired by a dry-erase doodling clock that he built a few years ago as a joke, Ekaggrat Kalsi decided to do something a little different. The Maker had found his previous gadget to be so mesmerizing that he wanted to transform it into a practical, everyday desk accessory.


For this, the mechanism needed to be a bit more reliable, aesthetically pleasing, and of course, accurate. This got him to thinking: Why not use a magnetic drawing board that could perpetually jot down the hours and minutes?

Based on an ATmega644P, the Maker’s new time-writing machine consists of a Magna Doodle display, a robotic arm controlled by a pair of 1:100 geared 15mm stepper motors, and two solenoids with cylindrical magnets on the end of the arm. The motors are handled by a standard StepStick, while the coils are driven by an L293DD Dual H-Bridge. It should also be noted that the project’s kinematics was solved with the help a fellow user on the RepRap forum.


Before arriving at his latest product, Kalsi devised two prototypes. The first one employed a motor on the base and another motor mounted to the arm, which drove the upper arm by a thin cable. The end result wasn’t as precise as he’d like. For the second iteration, the Maker swapped out the cable for a connecting rod, as the cable kept slipping. Still not perfect. And now, there’s this… See it in action below!

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