The GummiArm Project: A Replicable and Variable-Stiffness Robot Arm for Experiments on Embodied AI

Abstract

Robots used in research on Embodied AI often need to physically explore the world, to fail in the process, and to develop from such experiences. Most research robots are unfortunately too stiff to safely absorb impacts, too expensive to repair if broken repeatedly, and are never operated without the red kill-switch prominently displayed. The GummiArm Project was intended to be an open-source “soft” robot arm with human-inspired tendon actuation, sufficient dexterity for simple manipulation tasks, and with an eye on enabling easy replication of robotics experiments. The arm offers variable-stiffness and damped actuation, which lowers the potential for damage, and which enables new research opportunities in Embodied AI. The arm structure is printable on hobby-grade 3D printers for ease of manufacture, exploits stretchable composite tendons for robustness to impacts, and has a repair-cycle of minutes when something does break. The material cost of the arm is less than $6000, while the full set of structural parts, the ones most likely to break, can be printed with less than $20 worth of plastic filament. All this promotes a concurrent approach to the design of “brain” and “body,” and can help increase productivity and reproducibility in Embodied AI research. In this work we describe the motivation for, and the development and application of, this 6 year project.

Design and Prototyping of a 3DOF Worm-drive Robot Arm

“…One approach involves building inherent compliance into their designs [9,10]. One such design, the Gummiarm, achieves this by making use of compliant non-linear tendons driven by Dynamixels [11,12]. However, incorporating passive compliance can often compromise performance.…”

Design and prototyping of a low-cost light weight fixed-endpoint orientation planar Cobot

“…Firstly, arms can be made inherently compliant [7,8]. This approach was taken with the Gummiarm [9,10]. However, the introduction of passive compliance can often affect performance.…”

“…There are many other ways of implementing safety features in robotic arms other than force monitoring adopted in Cobots [11]. Some approaches, in particular the Gummiarm, have used co-contracting tendons which offer a means to implement passive variable stiffness actuation [9,10] and some recent work has investigated the dynamics and control of such a joint using state feedback control [18] and industrial controllers [19]. Passive compliance has a big advantage of making a mechanism resistant to impulsive disturbances, such as physical knocks, which are hard to deal with active compliance due to the limited controller bandwidth.…”