ERRoS: Energetic and Reactive Robotic Swarms 1
1 Introduction and Background As articulated in a recent presentation by the Deputy Assistant Secretary of the Army for Research and Technology, the future force projection of the United States Army relies heavily on the seamless integration of, and coordination between, manned and unmanned mobile platforms which collectively have a high degree of situational awareness and can sense, decide, and act/strike faster than adversarial forces [1]. To realize this forward-looking vision of manned-unmanned teaming, it is critical for research to advance on a number of closely-related topical fronts, including, but not limited to, networked communications; sensor fusion; GPS-denied navigation; multi-agent control; energetic and reactive materials and structures; and swarm robotics. In light of this reality, the present effort seeks to advance basic research understanding in the latter categories through the systematic development of Energetic and Reactive Robotic Swarms (ERRoS). Specifically, the effort seeks to leverage recent advancements in the additive manufacturing of reactive materials to fabricate energetic and reactive structures, which can be integrated with novel initiation systems and commercial off-the-shelf (COTS) hardware to create compact, unmanned aerial and ground vehicles. These vehicles will, in turn, be integrated in heterogeneous swarms via new control algorithms, to preliminarily assess the feasibility of ERRoS as a fieldable platform. Spanning both basic and more applied research tasks, the proposed effort will be guided by the following research questions: Do the PI s existing metal/fluoropolymer composite materials used in conjunction with conventional fused deposition modeling systems have adequate structural properties? How can one control for, or even potentially exploit, the structural-level realities, such as structural inhomogeneities, warping, and buckling, that can exist with these elements? Are fluorinated carbon fiber systems feasible alternatives to the aforemention material system? How does their performance compare? How can structural design (e.g., controlled structural confinement and gas jetting pathways) be used to enhance the energetic/reactive performance of reactive structures? What are the tradeoffs (if any) from a structural perspective of these design features? What material systems/structural element designs yield an optimal balance between strength, stability, and thermodynamic/reactive performance? Can additively manufactured initiation systems be developed for use with structural energetic and reactive materials? What attributes must these systems have? Can compact unmanned aerial and ground vehicles fabricated principally from structural energetic and reactive materials be created? What are the system-level performance characteristics of these robotic platforms? How can an operator control heterogeneous robotic swarms, when the number of robots far exceeds the number of operators? Are these control strategies feasible for use in GPS-denied operational environments? If not, can suitable alternates be developed? By successfully addressing these key questions, the PIs will not only advance the technical capabilities of the United States Army, but also advance the basic research understanding of energetic and reactive structural material systems and heterogeneous robotic swarms, both which are of distinct and increasing value to the Department of Defense, and the Army in particular. 2
Figure 1: (right) A portion of an unmanned aerial vehicle. (left) A close-up view of a structural component and a scaled (75%) reconstruction 3D printed on a commercial fused deposition system using a proprietary Al/PVDF filament. Figure 2: Video frames acquired during the controlled deflagration of the component ( 10 g) shown in Figure 1. This material system, which was not optimized from an energetic perspective released appreciable energy and left no meaningful remnants. 3
2 Proposed Technical Approach Generally speaking, the proposed basic and applied research effort consists of three main thrusts: (1) fabricating energetic and reactive structures and characterizing their performance from strength, stability, and combustion perspectives; (2) fabricating and characterizing ignition systems suitable for use with the aforementioned structural elements; and (3) constructing a heterogeneous swarm of unmanned aerial and ground vehicles, which can be controlled in a GPS-denied environment. As part of Thrust 1, the PIs will leverage their prior experience related to the development of metal/fluoropolymer composite materials that are amenable for use with commercial fused deposition modeling systems to 3D print prototypical structural elements [2]. In contrast to other ongoing work by the PIs, the focus here will not be on material characterization, but rather the structural characterization of trusses, beams, and plates with particular emphasis placed on their strength, stability (i.e., warping and buckling), and energetic/reactive performance. A key component of this task will be exploring how these three, often conflicting, performance metrics change if alternate material systems are used (e.g., fluorinated carbon fiber, nanoscale metal/fluoropolymer composites, or mechanically-activated metal/fluropolymer composites). In addition, the PIs will investigate the potential to utilize structural design to enhance energetic/reactive performance through reaction confinement (e.g., using enclosed truss geometries to create low explosive effects) and gas jetting pathways. Particular consideration will also be given to the aging of the structural components, and how their performance changes as a function of time, as their operational lifetime is likely of practical consideration. Concurrent with the aforementioned activities, as part of Thrust 2, the PIs will explore various printable initiator concepts based on electrically-conductive fused deposition modeling filaments. This effort will build upon the PIs recent work on inkjet printed initiation systems by exploring whether or not these systems can be co-fabricated with the structural elements delineated above using bridge wire or spark gap form factors. A particular research challenge here is the development of an electrical initiation system that is reliable, operates on a stringent power budget (set by the untethered mobile form factor), and is easily fabricated and integrated. The potential of electrically-conductive energetic and reactive elements will also be assessed as part of this thrust. Finally, in Thrust 3, the PI s will leverage the extensive experience of Co-PI Cappelleri in the development of custom designed and fabricated aerial and terrestrial robots composed principally of energetic and reactive structural materials and commercial off-the-shelf components. Specifically, the PIs will adapt Cappelleri s most recent aerial robot platform (the I-BoomCopter) [3, 4] and a modified TurtleBot3 platform such that most, if not all, of the structural components are replaced with energetic or reactive counterparts (see Figures 1-3). As currently designed, these systems have appreciable range (e.g., the I-BoomCopter has 8.8 km of range in its current configuration when using a single battery) and allow for autonomous movement or teleoperation. As part of the current effort, the ranges will be extended, and the control architectures bulked up to allow for operation in GPS-denied environments, as enabled through direct robot-to-robot communication and periodic interface with an operator. This will be done within a framework of shared autonomy, wherein some system operations will be performed autonomously, while others are carried out by the operators. This requires appreciable research in motion planning, control, machine learning, and human-robot interactions. Of specific interest will be shared autonomy control designs that 4
Figure 3: (left) The I-BoomCopter with pertinent performance metrics. (right) The proposed aerial and terrestrial platforms. off-load basic functions from the operators but do so in a way that still allows for fluent intervention, as needed, to complete complex mission objectives. 3 Impact on the Department of Defense Additively manufactured energetic and reactive structural materials have the potential to fundamentally change the capabilities of the Department of Defense, due to not only to their potential use in unmanned systems, but their impact on future munition systems as a whole. However, this potential cannot be fully realized unless there exists both a fundamental understanding of the material-process-structure-function relationships associated with these structures, and a demonstration of their utility in a practical context this is the focus of the proposed work. 4 Team Organization, Capabilities, and Management Plan The proposed effort will leverage the experience of five PIs with distinct, yet complementary, expertise. Rhoads has expertise in the areas of dynamics and vibration, energetic materials, and additive manufacturing. He will be responsible for overall project management, and will guide the experimental characterization of the structural energetic and reactive elements, and design and fabricate the initiation systems. Cappelleri has expertise in motion planning, robotics and multi-agent control. He will be responsible for designing and assembling the robotic platforms and assessing their integration and performance. Gunduz has expertise in material science and additive manufacturing. He will be responsible for fabricating the structural elements. Son has expertise in energetic materials and their characterization. He will serve as a subject matter expert to ensure proper formulation, safety, and handling, and will be responsible for thermodynamic/reaction characterization. Finally, Chiu has expertise in mechatronics, sensor integration, and control. He will 5
be responsible for implementing the developed control architecture with COTS sensor packages. In the proposed effort, the PIs will meet weekly as a group, with their students, pooling their expertise to realize the stated research objectives. Reporting requirements will be addressed on a group basis, with the PI having ultimate authority on all deliverables. It should be noted that the PIs have an extensive record of collaboration, as demonstrated through a number of joint publications, and the co-advising of multiple graduate research assistants. Additionally, the PIs have contributed to and successfully led multiple, large Department of Defense sponsored initiatives. To achieve the stated research objectives the PIs will leverage the unique experimental capabilities of the Ray W. Herrick Laboratories and Maurice J. Zucrow at Purdue University. For more information on these facilities, please visit: www.engineering.purdue.edu/herrick and www.engineering.purdue.edu/zucrow. 5 Summary of Estimated Costs The proposed, three-year activity is estimated to have a budget of TBD. These funds will be used for student, post-doc, and faculty support; the creation of a new remote fabrication, characterization, and storage space (necessary due to the kilograms of material that will be fabricated); the creation of a new remote robotics course suitable for use with energetic and reactive materials; remotely operated extruders and printers; consumable supplies; and travel to relevant technical meetings. References 1. T. Russell. Purdue Energetic Materials Summit. 2017. 2. T. J. Fleck, et al. Additive Manufacturing. 2017. Submitted. 3. D. McArthur, et al. IEEE International Conference on Robotics and Automation. 2017. 4. D. McArthur, et al. ASME International Design Engineering Technical Conferences. 2017 6