In the world of industrial robots, six-axis models are perhaps what comes to mind. However, SCARA – Selective Compliance Assembly/Articulated Robot Arms – are also quite common, for applications where complicated 3D orientation isn’t needed. While these machines can cost many thousands of dollars, and are normally refined over years of work, YouTuber How To Mechatronics created a version of his own using four NEMA 17 motors and an array of 3D-printed components.
As seen in the video below, the device employs timing belts and pulleys inside the segments for power transmission and gear reduction in the horizontal direction. The Z-axis is driven by another stepper, along with a lead screw, held in place with a series of four rods and linear ball bearings. For the "hand" portion, a servo motor controls an end effector, enabling it to pick and place objects as necessary.
The robot is controlled via an Arduino Uno, with a CNC shield and four A4988 stepper drivers to move the servos directly. User interface is via a nearby laptop, running Processing code that lets one adjust positions using forward and inverse kinematics, as well as the speed and acceleration. The interface allows movements to be stored and repeated, manipulating objects automatically!