3D Printed Mechanically Modular Two-Degree-Of-Freedom Robotic Segment Utilizing Variable-Stiffness Actuators

Here we describe the initial development of a 3D printed modular robotic segment that is driven by variable stiffness actuators (VSAs). The novelty of the presented work is the combination of cost-effective antagonist VSAs with mechanical modularity: this enables multiple segments to be used either as a stand-alone serpentine robot or as compliant joints that can easily be integrated into other robotic systems. The VSAs are comprised of antagonist DC motor pairs that separately actuate two orthogonal revolute joints via a viscoelastic tendon-based transmission system. The simplistic nature of the design also aims to minimize the effects of joint coupling. Joint-level control is performed on a microcontroller which transmits motor current and joint position information over USB to a computer. ROS packages, including those needed for Gazebo and MoveIt! were created to enable physics simulations and motion-planning of either a single isolated segment, multiple chained segments, or some combination of segments and other robotic devices. We present results of a preliminary physical prototype of one such robotic segment whose joint positions and co-contractions were manually controlled using a gamepad and subsequently visualized using the developed ROS packages. The dynamics of the VSA were analyzed and the joint-torque equations were derived as functions of tendon parameters, joint angles, and motor electrical characteristics