The Mechpen SCARA Plotter

We’ve seen a variety of ‘drawbots’ here at hackster, but this SCARA (Selective Compliance Assembly Robot Arm)-style plotting arm is certainly one of a kind. With its combined shoulder and elbow joints, the robot is able to reach out at up to 140 cm, allowing it to cover a piece of A0 Paper.

The first challenge with creating such a ’bot is how to keep weight down in order to prevent it from sagging too much at the end, as well as to keep it controllable. As such, creator Alex Weber went so as to drill “lots of holes in almost every part f the arm to save some weight.” He used 6mm carbon tubes to form the arm frame, with diagonal tubes added in the upper arm for greater support. Even this, employing a tiny 180D servo to activate the pen on the end wasn’t enough to keep the pen on the end from sagging, however. To remedy the situation, he utilized a VL6180X distance sensor to get a grid of height values, the same sort of process used to level 3D printer beds.

Like many 3D printers, the device is controlled by OctoPrint running on a Raspberry Pi, which allows Weber to upload G-code and start print files over WiFi. An Einsy RAMBo board — which is also generally used for 3D printers — is used to handle the two NEMA 23 stepper motors that drive arm movement. Gear reduction, along with 1/32nd stepping, is used to provide an impressive effective resolution of 177.778 steps per degree.

It’s beautifully demonstrated in action in the first video below, and the second shows clips of the build process.

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Author: Jeremy S. Cook

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