ATRIAS is a human-scale 3D-capable bipedal robot designed to mechanically embody the

We present a reduced-order approach for dynamic and efficient bipedal control, culminating in 3D balancing and walking with ATRIAS, a heavily underactuated bipedal robot. These results are a development toward solving a number of enduring challenges in bipedal locomotion: achieving robust 3D gaits at various speeds and transitioning between them, all while minimally draining on-board energy supplies. Our reduced-order control methodology works by extracting and exploiting general dynamical behaviors from the spring-mass model of bipedal walking. When implemented on a robot with spring-mass passive dynamics, e.g. ATRIAS, this controller is sufficiently robust to balance while subjected to pushes, kicks, and successive dodge-ball strikes. The controller further allowed smooth transitions between stepping in place and walking at a variety of speeds (up to 1.2 m/s). The resulting gait dynamics also match qualitatively to the reduced-order model, and additionally, measurements of human walking. We argue that the presented locomotion performance is compelling evidence of the effectiveness of the presented approach; both the control concepts and the practice of building robots with passive dynamics to accommodate them.

Despite enhancements in the development of robotic systems, the energy economy of today's robots lags far behind that of biological systems. This is in particular critical for untethered legged robot locomotion. To elucidate the current stage of energy efficiency in legged robotic systems, this paper provides an overview on recent advancements in development of such platforms. The covered different perspectives include actuation, leg structure, control and locomotion principles. We review various robotic actuators exploiting compliance in series and in parallel with the drive-train to permit energy recycling during locomotion. We discuss the importance of limb segmentation under efficiency aspects and with respect to design, dynamics analysis and control of legged robots. This paper also reviews a number of control approaches allowing for energy efficient locomotion of robots by exploiting the natural dynamics of the system, and by utilizing optimal control approaches targeting locomotion expenditure. To this end, a set of locomotion principles elaborating on models for energetics, dynamics, and of the systems is studied.

B iological bipeds have long been thought to take advantage of compliance and passive dynamics to walk and run, but realizing robotic locomotion in this fashion has been difficult in practice. Assume The Robot Is A Sphere (ATRIAS) is a bipedal robot designed to take advantage of the inherent stabilizing effects that emerge as a result of tuned mechanical com pliance (Table 1). In this article, we describe the mechanics of the biped and how our controller exploits the interplay bet ween passive dynamics and actuation to achieve robust locomotion. We outline our development process for the incremental design and testing of our controllers through rapid iteration. By show time at the Defense Advanced Research Pro jects Agency (DARPA) Robotics Challenge (Figure 1), ATRIAS was able to walk with robustness, locomote in ter rain from asphalt to grass to artificial turf, and traverse changes in surface height as large as 15 cm without planning or visual feedback. Furthermore, ATRIAS can accelerate from rest, transition smoothly to a running gait, and reach a top speed of 2.5 m/s (9 km/h). Reliably achieving such dynamic locomotion in an uncertain environment required rigorous development and testing of the hardware, software, and control algorithms. This endeavor culminated in seven live shows of ATRIAS walking and running, with disturbances and without falling, in front of a live audience at the DARPA Robotics Challenge. Approaches to Biped Control Walking and running on two legs is an enduring challenge in robotics. Avoiding falls becomes especially tricky when the terrain is uncertain in both its geometry and rigidity. A promising approach to achieving stable control is to relin quish some authority to purposeful passive dynamics, per haps by adding mechanical compliance [1] or removing actuators entirely [2]. If the machine's unactuated dynam ics are thoughtfully designed, they can passively attenuate disturbances and require smaller adjustments from the controller [33].