The best robots are robots that can do a job. To paraphrase a source I can’t remember, robots that are good at their jobs eventually become appliances. Your inkjet printer, for instance, fits most definitions of a “robot.” If you want some more proof, check out Ivan Miranda’s 3D-printed robotic permanent marker printer.
This is basically a robot that only moves in one direction, and drags permanent markers behind it to print out a picture. There are a total of 16 large permanent markers that have been arranged in two rows. Each of those markers is mounted on a servo arm, so the robot can raise the marker up and down onto the sheet of paper. As the robot drives along, it touches the markers to the paper to plot out simple images.
Those servos are controlled by an Arduino Mega through four motor drivers. All of that is mounted on a 3D-printed frame, which is moved by a pair of beefy gearmotors. In theory, this is a pretty straightforward build. But, as Miranda demonstrates, the machine is quite finicky. Getting the markers to touch the paper well — and then lift off properly — was a big challenge.
In Miranda’s second and third videos on the permanent marker printer, he shows how tricky that is to accomplish. The markers either pushed too hard on the paper and lifted the entire robot up, or didn’t make solid contact. But, after a few design changes and a lot of fine-tuning, he was able to get it printing somewhat recognizable pictures. Miranda has plans to further improve the design, so be sure to follow along with his progress!