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We introduce an agility measure enabling the comparison of two very different leaping-from-rest transitions by two comparably powered but morphologically different legged robots. We use the measure to show that a flexible spine outperforms a rigid back in the leaping-from-rest task. The agility measure also sheds light on the source of this benefit: core actuation through a sufficiently powerful parallel elastic actuated spine outperforms a similar power budget applied either only to preload the spine or only to actuate the spine during the leap, as well as a rigid backed configuration of the identical machine. Abstract. We introduce an agility measure enabling the comparison of two very di↵erent leaping-from-rest transitions by two comparably powered but morphologically di↵erent legged robots. We use the measure to show that a flexible spine outperforms a rigid back in the leapingfrom-rest task. The agility measure also sheds light on the source of this benefit: core actuation through a su ciently powerful parallel elastic actuated spine outperforms a similar power budget applied either only to preload the spine or only to actuate the spine during the leap, as well as a rigid backed configuration of the identical machine. Disciplines Electrical and Computer Engineering | Engineering | Systems Engineering

In the field of haptics, conditions for mechanical "transparency"[1] entail such qualities as "solid virtual objects must feel stiff" and "free space must feel free"[2], suggesting that a suitable actuator is able both to do work and readily have work done on it. In this context, seeking actuator transparency has come to mean a preference for minimal dynamics [3] or no impedance [4]. While such general notions seem satisfactory for a haptic interface, actuators with good mechanical transparency are now being used in high-performance robots [5, 6] where once again they must be able to do work, but are now also expected to perceive their environment by processing signals related to contact forces in the leg or manipulator when an explicit force sensor is not present. As robotics researchers develop models [7] suitable for programming behaviors that require systematic making and breaking of contact within the environments on which they perform work, actuators must be capable of: (a) generating the high forces at speed needed to accelerate the body during locomotion [5]; (b) robustness to high forces and impacts during locomotion [8]; (c) perceiving high force events quickly, such as touchdown in stance [9]; (d) perceiving contact quickly without exerting significant force on the object, such as in gentle manipulation [10]; and (e) reacting quickly during time-sensitive behaviors [11]. This work aims to describe a quantitative assay of transparency that might, for example, predict the advantage in proprioceptive tasks of an electromagnetic directdrive (DD) motor (i.e., one without gearbox), relative to actuation schemes consisting of both a motor and a geared reduction. Specifically, we explore the prospects for characterizing transparency as revealed by comparing the energetic cost of "feeling" the environment. Our sample proprioceptive task is instantiated by a simple torque estimator in Sec. 2. This scheme is then instrumented in simple contact detection experiments paired with a model to empirically explore the relationships between collision energy and detection time delay in Sec. 3. The actuators are then tested with a feel-cage task to illustrate the advantage of good transparency in Sec. 4.

This paper contributes to quantifying the notion of robotic fitness by developing a set of necessary conditions that determine whether a small quadruped has the ability to open a class of doors or climb a class of stairs using only quasi-static maneuvers. After verifying that several such machines from the recent robotics literature are mismatched in this sense to the common human scale environment, we present empirical workarounds for the Minitaur quadrupedal platform that enable it to leap up, force the door handle and push through the door, as well as bound up the stairs, thereby accomplishing through dynamical maneuvers otherwise (i.e., quasi-statically) achievable tasks. Abstract-This paper contributes to quantifying the notion of robotic fitness by developing a set of necessary conditions that determine whether a small quadruped has the ability to open a class of doors or climb a class of stairs using only quasi-static maneuvers. After verifying that several such machines from the recent robotics literature are mismatched in this sense to the common human scale environment, we present empirical workarounds for the Minitaur quadrupedal platform that enable it to leap up, force the door handle and push through the door, as well as bound up the stairs, thereby accomplishing through dynamical maneuvers otherwise (i.e., quasi-statically) unachievable tasks.

This paper examines the design of a parallel spring-loaded actuated linkage intended for dynamically dexterous legged robotics applications. Targeted at toe placement in the sagittal plane, the mechanism applies two direct-drive brushless dc motors to a symmetric five bar linkage arranged to power free tangential motion and compliant radial motion associated with running, leaping, and related agile locomotion behaviors. Whereas traditional leg design typically decouples the consideration of motor sizing, kinematics and compliance, we examine their conjoined influence on three key characteristics of the legged locomotion cycle: transducing battery energy to body energy during stance; mitigating collision losses upon toe touchdown; and storing and harvesting prior body energy in the spring during stance. This analysis leads to an unconventional design whose "knee" joint rides above the "hip" joint. Experiments demonstrate that the resulting mechanism can deliver more than half again as much kinetic energy to the body (or more than double the kinetic energy if the full workspace is used), and offers a five-fold increase in energy storage and collision efficiency relative to the conventional design. Abstract-This paper examines the design of a parallel spring-loaded actuated linkage intended for dynamically dexterous legged robotics applications. Targeted at toe placement in the sagittal plane, the mechanism applies two direct-drive brushless dc motors to a symmetric five bar linkage arranged to power free tangential motion and compliant radial motion associated with running, leaping, and related agile locomotion behaviors. Whereas traditional leg design typically decouples the consideration of motor sizing, kinematics and compliance, we examine their conjoined influence on three key characteristics of the legged locomotion cycle: transducing battery energy to body energy during stance; mitigating collision losses upon toe touchdown; and storing and harvesting prior body energy in the spring during stance. This analysis leads to an unconventional design whose "knee" joint rides above the "hip" joint. Experiments demonstrate that the resulting mechanism can deliver more than half again as much kinetic energy to the body (or more than double the kinetic energy if the full workspace is used), and offers a five-fold increase in energy storage and collision efficiency relative to the conventional design.