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Pseudonymous engineer and YouTuber "Skyentific" has built what he describes as a "strange robot arm," based on a virtual sphere design and using Dynamixel servos and an OpenRB-150 controller — resulting in a device that can contort itself in novel ways. Mechanical Robot Arm

Skyentific's Virtual Sphere Rolling Joint Gives This 3D-Printed Robot Arm Mesmerizing Motion - Hackster.io

"I have built [a] very unusual robotic arm," Skyentific explains of his latest project, which blends off-the-shelf parts with a 3D-printed framework. "Its unique design allows for the organic motions, which are not accessible to other robots."

The robot arm's design is based on a "virtual sphere rolling joint" building up from a simple hinge-joint to a rolling joint with one degree of freedom before adding a second degree of freedom. "It moves like two spheres rolling one on another," Skyentific explains, "but from [a] mathematical point of view these are not really spheres — so this is just an approximation of the rolling sphere joint."

Taking three virtual rolling sphere joint stages and joining them together creates a robot arm with six degrees of freedom — but capable of expressing those freedoms in a manner, which resembles a snake or an elephant's trunk more than a traditionally-jointed 6DoF robot arm.

"This is already the third prototype," Skyentific adds. "This robot arm is going to be a kind of test robot arm, so I don't want to make it expensive — and that's why this particular [design] is not very suitable, because it's quite bulky, it's big and it's heavy, and I would like to use quite inexpensive servos to drive this robot [but] the servos need to be quite precise, and that's why I chose the Dynamixel servos [at] around $50 per servo."

A video showcasing the design is now up on the Skyentific YouTube channel, while CAD files are available to Skyentific's Patreon backers but have not yet been released publicly.