This paper presents the design of the hydraulically actuated quadruped robot HyQ2Max. HyQ2Max is an evolution of the 80kg agile and versatile robot HyQ. Compared to HyQ, the new robot needs to be more rugged, more powerful and extend the existing locomotion skills with self-righting capability. Since the robot's actuation system has an impact on many aspects of the overall design/specifications of the robot (e.g. payload, speed, torque, overall mass, compactness), this paper will pay special attention to the selection and sizing of the joint actuators. To obtain meaningful joint requirements for the new machine, we simulated 7 characteristic motions that cover a wide range of required behaviors of an agile rough terrain robot, including trotting on rough terrain, stair climbing, push recovery, self-righting, etc. We will describe how to use the obtained joint requirements for the selection of the hydraulic actuator types, four-bar linkage parameters and valve size. Poorly sized actuators may lead to limited robot capabilities or higher cost, weight, energy consumption and cooling requirements. The main contributions of this paper are (1) a novel design of an agile quadruped robot capable of performing trotting/crawling over flat/uneven terrain, balancing and self-righting; (2) a detailed method to find suitable hydraulic cylinder/valve properties and linkage parameters with a specific focus on optimizing the actuator areas; and (3) to the best knowledge of the authors, the most complete review of hydraulic quadruped robots.

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A common disadvantage of quadruped robots is that they are often limited to load carrying or observation tasks, due to their lack of manipulation capability. To remove this limitation, arms can be added to the body of the robot, enabling manipulation and providing assistance to the robot during body stabilization. However, a suitable arm for a quadruped platform requires specific features which might not all be available in off-the-shelf manipulators (e.g. speed, torque-controlled, lightweight , compact, without external control unit). In this paper, we present a systematic approach to design a robotic arm tailored for an 80kg quadruped robot. A full robot with arms and legs (aiming for a centaur-style robot) was simulated performing a range of "representative" tasks to estimate joint torques and velocities. This data was then extensively used to select the design parameters, such as the joint actuators to develop a novel, compact (0.743m fully extended), lightweight (12.5kg), and fast (maximum 4m/s no-load speed at end-effector) hydraulically actuated robotic arm with 6 torque-controlled degrees of freedom. The enclosed video presents preliminary experimental results.

Geoff Parker’s investigations of the yellow dung fly mating system revitalized interest in sexual selection theory, sparked development of sperm competition and sexual conflict theories, and stimulated use of this species as an important model system. Numerous studies across widespread populations have demonstrated large-male advantages in competition contests occurring on dung in cow pastures; however, recent work suggests that smaller males adopt an alternative mating tactic by avoiding dung and instead copulating with females at foraging sites. Though this finding has the potential to expand our understanding of sexual selection in yellow dung flies, such behavior has to date been documented at only one field site, raising the possibility that this phenomenon is highly localized. Here, we report the expression of size-dependent alternative mating tactics across three discrete populations. These findings provide a cautionary tale for researchers limiting their attention to aggregation sites where study organisms are most conveniently encountered.

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