Using the art practice of play to communicate legged robotics research concepts

The art practice of play uses spontaneity and surprise to communicate meaningful content and inspire critical thinking (1-3). We describe three engineering education outreach efforts that use play to communicate legged robotics research concepts. In the first workshop, Penn engineering students were motivated to learn how to program a legged robot using the narrative of a “dance competition,” with the winning dances to be showcased at the Philadelphia Science Festival. In the second workshop, Philadelphia School District high school students used a poseably programmable legged robot to tell a story by performing a series of behaviors in a set of their own design and documenting the story as a video artwork. Here, there were two narratives: One created by the workshop directors, communicating concepts about complex multi-legged behaviors and gaits, and the other created by the students using the robots to express their ideas. In the final workshop, middle school students created locomoting robots using motors, post-consumer materials, and basic art supplies. The concepts of energy and physical programming were demonstrated using working Trashbots and practiced during an introductory exercise making a vibrating motor from a spinning one. Participants then created a robot of their own design using iterative experimentation. We conclude from these three workshops that play can be used as a vehicle for scientific communication. (1) David Getsy, ed. From diversion to subversion: Games, play, and twentieth-century art, Vol. 16 (Penn State Press, 2011). (2) Nato Thompson and Gregory Scholette, eds. The interventionists: Users\u27 manual for the creative disruption of everyday life (MIT Press, 2004). (3) Diedra Krieger, ‘Plastic Fantastic,’ Gyre Exhibition, Anchorage Museum, Alaska, 2014. For more information: Kod*lab

Mitigating energy loss in a robot hopping on a physically emulated dissipative substrate

We work with geoscientists studying erosion and desertification to improve the spatial and temporal resolution of their data collection over long transects in difficult realworld environments such as deserts. The Minitaur robot, which can run quickly over uneven terrain and use a single leg to measure relevant ground properties such as stiffness, is an attractive scout robot candidate for inclusion in a heterogeneous team in collaboration with a heavily geared, sensor-laden RHex. However, Minitaur is challenged by long-distance locomotion on sand dunes. Previous simulation results suggested that the energetic cost of transport can be mitigated by programming a virtual damping force to slow the intrusion of a Minitaur foot into simulated granular media following a bulk-behavior force law. In this paper, we present a ground emulator that can be used to test such locomotion hypotheses with a physical single-legged hopper jumping on emulated ground programmed to exhibit any compliance and damping characteristics of interest. The new emulator allows us to corroborate the conclusions of our previous simulation with physical hopping experiments. Programming the substrate emulator to exhibit the mechanics of a simplified bulk-behavior model of granular media characterized by linear stiffness and quadratic damping, we achieve a consistent energy savings of 20% in comparison with a nominal controller, with savings of up to 50% under specific conditions. For more information, see https://kodlab.seas.upenn.edu

Reactive Velocity Control Reduces Energetic Cost of Jumping with a Virtual Leg Spring on Simulated Granular Media

Robots capable of dynamic locomotion behaviors and high-bandwidth sensing with their limbs have a high cost of transport, especially when locomoting over highly dissipative substrates such as sand. We formulate the problem of reducing the energetic cost of locomotion by a Minitaur robot on sand, reacting to robot state variables in the inertial world frame without modeling the ground online. Using a bulk-behavior model of high-velocity intrusions into dry granular media, we simulated single jumps by a one-legged hopper using a Raibert-style compression-extension virtual leg spring. We compose this controller with a controller that added damping to the leg spring in proportion to the intrusion velocity of the robot\u27s foot into the simulated sand while the robot is pushing off in the second half of stance. This has the effect of both reducing the torque exerted by the motors because the added virtual active damping force acts in opposition to the virtual leg spring force, and reducing the transfer of energy from the robot to the sand by slowing the intrusion velocity of the foot. Varying the simulated robot\u27s initial conditions and the simulated ground parameters, we gained a consistent 20% energy savings by adding active damping with no cost in apex height. For more information, see the Kod*lab website: kodlab.seas.upenn.ed

RHex Slips on Granular Media

RHex is one of very few legged robots being used for realworld rough-terrain locomotion applications. From its early days, RHex has been shown to locomote successfully over obstacles higher than its own hip height [1], and more recently, on sand [2] and sand dunes [3], [4] (see Figure 1). The commercial version of RHex made by Boston Dynamics has been demonstrated in a variety of difficult, natural terrains such as branches, culverts, and rocks, and has been shipped to Afghanistan, ostensibly for use in mine clearing in sandy environments [5]. Here, we discuss recent qualitative observations of an updated research version of RHex [6] slipping at the toes on two main types of difficult terrain: sand dunes and rubble piles. No lumped parameter (finite dimensional) formal model nor even a satisfactory computational model of RHexs locomotion on sand dunes or rubble piles currently exists. We briefly review the extent to which available physical theories describe legged locomotion on flat granular media and possible extensions to locomotion on sand dunes

Mechanical and virtual compliance for robot locomotion in a compliant world

This abstract was accepted to the Robot Design and Customization workshop at ICRA 2019. For more information: Kod*lab

Semi-continuous anaerobic digestion of the marine micro-algal species I. galbana and D. salina grown under low and high sulphate conditions

Anaerobic digestion of marine micro-algae is a necessary step for their incorporation into the future portfolio of biofuels. Digestion of marine feedstocks can pose operational issues associated with competition and toxicity to the microbial consortium. This research examined the marine species Isochrysis galbana and Dunaliella salina continuously cultivated in a tubular photobioreactor using a low sulphate medium; D. salina was also cultivated with a high sulphate medium (4.7 g SO4 L−1). Harvested micro-algal biomass was used as feedstock in semi-continuous digestion with a salt-adapted inoculum. Stable operation was achieved with reasonable specific methane production (SMP)despite a short (15-day)retention time. SMP for I. galbana and D. salina was 0.244 and 0.233 L CH4 g−1 volatile solids (VS), with VS destruction 32% and 48% respectively. SMP ranged from 62 to 94% of the biochemical methane potential, but was only 32–49% of theoretical methane yields, indicating pre-treatments may be beneficial. Changing from low to high sulphate D. salina reduced the SMP to 0.193 L CH4 g−1 VS with a rise in H2S production. Under semi-continuous digestion, evidence for sulphide precipitation and oxidation was observed, which were not seen in batch analyses. This highlights the importance of conducting continuous rather than batch studies, to avoid overlooking these effects.</p

Experimental Methods To Support Robot Behavior Design For Legged Locomotion On Granular Media

Most models of legged locomotion assume a rigid ground contact, but this is not a reasonable assumption for robots in unstructured, outdoor environments, and especially not for field robots in dry desert environments. Locomotion on sand, a highly dissipative substrate, presents the additional challenge of a high energetic cost of transport. Many legged robots can be adapted for desert locomotion by simple morphological changes like increasing foot size or gearing down the motors. However, the Minitaur robot has direct-drive (no gearbox) legs which are sensitive enough to measure ground properties of interest to geoscientists, and its legs would lose their sensitivity if they were geared down or the footsize increased substantially. This thesis has two main contributions. First, a controller for jumping on sand with a direct-drive robot that saves significant energy in comparison to a nominal compression-extension Raibert-style controller without sacrificing jump height. This controller was developed by examining the complex interaction between the jumping leg and the ground, and devising a force to add to the leg controller which will push the robot’s foot into a more favorable state that does not transfer as much energy to the ground. The second contribution is a ground emulator robot which can be programmed to exert ground force functions of arbitrary shape. With the ground emulator, it is possible for a robot on a linear rail to jump dozens of times per experiment, whereas traditional experiments on granular media would require the ground to be reset between individual jumps. Results from the simulation experiments used to develop the controller and the ground emulator experiments used to test it on a physical robot leg are validated with experiments on a prepared granular media bed. Finally, the contributions of this thesis are contextualized in a broader project of building explainable artificially intelligent systems by composing robust, mostly reactive controllers

Comparative testing of energy yields from micro-algal biomass cultures processed via anaerobic digestion

Although digestion of micro-algal biomass was first suggested in the 1950s, there is still only limited information available for assessment of its potential. The research examined six laboratory-grown marine and freshwater micro-algae and two samples from large-scale cultivation systems. Biomass composition was characterised to allow prediction of potentially available energy using the Buswell equation, with calorific values as a benchmark for energy recovery. Biochemical methane potential tests were analysed using a pseudo-parallel first order model to estimate kinetic coefficients and proportions of readily-biodegradable carbon. Chemical composition was used to assess potential interferences from nitrogen and sulphur components. Volatile solids (VS) conversion to methane showed a broad range, from 0.161 to 0.435 L CH4 g?1 VS; while conversion of calorific value ranged from 26.4 to 79.2%. Methane productivity of laboratory-grown species was estimated from growth rate, measured by changes in optical density in batch culture, and biomass yield based on an assumed harvested solids content. Volumetric productivity was 0.04–0.08 L CH4 L?1 culture day?1, the highest from the marine species Thalassiosira pseudonana. Estimated methane productivity of the large-scale raceway was lower at 0.01 L CH4 L?1 day?1. The approach used offers a means of screening for methane productivity per unit of cultivation under standard conditions