The Graphotron Mini Makerfaire Robot

This little gadget is the graphotron 6000/graphotron 8000/remote drawing robot. The makerspace I’ve been frequenting wanted a little robot thing to display at a Mini Makerfaire and they tasked me with the project about 26 hours before it was due. I enjoy these hackathon-style binges once in a while.

I started out with a basic Arduino Uno, a handful of servos, and an equal amount of potentiometers. The initial goal was to build a remote-operated robot that plays Operation, kind of like a really dumb DaVinci surgical robot. Problems arose with figuring out the end-effector so after talking it over with the client, the Duh-Vinci became the Graphotron. The makerspace specializes in art, so drawing just kind of made sense.

The arm is a (potentially) 4 DOF manipulator made of hobby servos, dowels, and 3D printed structural components. I say potentially 4 DOF because I had some weird issues with controlling the end-effector servo dynamically, so I just stuck it at 120 degrees (or something) to hold the pen steady. The three bigger servos towards the base of the arm run on 6V, so they needed some unique regulation down from the 12V I was using. Variable voltage regulators were the solution there. The little guy on the end only needed 5V, so I used a pretty generic 5V regulator for that.

The controller, as I’ve been calling it, is almost identical to the arm in terms of dimensions to make it easier to translate the controller motion to the arm. There’s a potentiometer at each joint which measures the angles for the arm to mimic. Structurally, it consists of the same dowels and 3D printed plastic as the arm.

On the software side, linking the arm to the controller was probably as easy as it could possibly be. The Arduino measured each potentiometer on the controller and moved each corresponding servo on the arm to the same angle. Basically, it’s the Servo Knob example three times.

All-in-all the Graphotron was a hit with the kiddos. Actually using the gadget is as simple as using a pen; however, getting the result you want on the arm side is not easy due to the servos being the cheapest I could find and the angles between the potentiometers and the servos not being 1:1. The adopted slogan was “It’s like drawing, but if your hand had no nerves and your muscles only cost $60”. Super catchy.