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1. PuzzleFlex: Kinematic Motion of Chains with Loose Joints

   Lensgraf, Samuel; Itani, Karim; Zhang, Yinan; Sun, Zezhou; Wu, Yijia; Li, Alberto Q.; Zhu, Bo; Whiting, Emily; Wang, Weifu; Balkcom, Devin (January 2020, International Conference on Robotics and Automation (ICRA))

   This paper presents a method of computing free motions of a planar assembly of rigid bodies connected by loose joints. Joints are modeled using local distance constraints, which are then linearized with respect to configuration space velocities, yielding a linear programming formulation that allows analysis of systems with thousands of rigid bodies. Potential applications include analysis of collections of modular robots, structural stability perturbation analysis, tolerance analysis for mechanical systems, and formation control of mobile robots. 

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2. A geometric characterization of observability in inertial parameter identification

   https://doi.org/10.1177/02783649241258215  

   Wensing, Patrick M; Niemeyer, Günter; Slotine, Jean-Jacques E (July 2024, The International Journal of Robotics Research)

   This paper presents an algorithm to geometrically characterize inertial parameter identifiability for an articulated robot. The geometric approach tests identifiability across the infinite space of configurations using only a finite set of conditions and without approximation. It can be applied to general open-chain kinematic trees ranging from industrial manipulators to legged robots, and it is the first solution for this broad set of systems that is provably correct. The high-level operation of the algorithm is based on a key observation: Undetectable changes in inertial parameters can be represented as sequences of inertial transfers across the joints. Drawing on the exponential parameterization of rigid-body kinematics, undetectable inertial transfers are analyzed in terms of observability from linear systems theory. This analysis can be applied recursively, and lends an overall complexity of O( N) to characterize parameter identifiability for a system of N bodies. Matlab source code for the new algorithm is provided. 

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3. The dynamics of a two link Chaplygin sleigh driven by an internal momentum wheel

   https://doi.org/10.23919/ACC.2017.7963274  

   Fedonyuk, Vitaliy; Tallapragada, Phanindra (May 2017, American Control Conference)

   A class of aquatic robots have been shown to have a correspondence to terrestrial nonholonomic systems. In particular bodies shaped as a Joukowski foil have been shown to have dynamics similar to a well known nonholonomic system, the Chaplygin sleigh. This inspires several related rigid body nonholonomic systems whose behavior is similar to other aquatic robots with other morphologies. In this paper we investigate the dynamics of one such nonholonomic system, a two-link Chaplygin sleigh that is controlled by an internal momentum wheel. This system is analogous to a similar aquatic robot with a passive tail. We also discuss results related to the accessibility and controllability of the two-link Chaplygin sleigh. 

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4. Bioinspired Model for Drosophila Larva Crawling Locomotion

   https://doi.org/10.1109/DCAS65331.2025.11045489  

   Perera, Dulanjana M; Byrd, Nathan; Huang, Yuhan; Le, Xuan Tung; Arachchige, Dimuthu_D K; Wang, Zhaosen; Zarin, Aref A; Godage, Isuru S (April 2025, IEEE)

   Fruit flies or Drosophila larvae exhibit a diverse range of locomotion gaits enabled by their soft, segmented bodies and intricate muscle arrangements. Their bodies, composed of multiple segments, are synchronously activated to propel forward through a combination of muscle elongation and contraction. Soft robotic systems, inspired by such biological marvels, face significant challenges in replicating these complex behaviors due to the intricate interplay between muscle activation, soft body dynamics, and frictional forces. To address these challenges, we propose a reduced-order model that captures the essential features of larval crawling. By modeling segments as a combination of prismatic and revolute joints, we can simulate the nonlinear motion resulting from muscle activation and body deformation. Our model demonstrates the potential of this approach to accurately describe larval movement, as validated by comparisons with actual larval trajectories. This research offers valuable insights into the design and control of soft robots and provides a framework for biologists to investigate the complex mechanisms of neuromuscular coordination in larvae. 

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5. Simulation and Fabrication of Soft Robots with Embedded Skeletons

   https://doi.org/10.1109/ICRA46639.2022.9811844  

   Bern, James M.; Zargarbashi, Fatemeh; Zhang, Annan; Hughes, Josie; Rus, Daniela (May 2022, Proceedings of the IEEE International Conference on Robotics and Automation)

   Soft robots can be incredibly robust and safe but typically fail to match the strength and precision of rigid robots. This dichotomy between soft and rigid is recently starting to break down, with emerging research interest in hybrid soft-rigid robots. In this work, we draw inspiration from Nature, which achieves the best of both worlds by coupling soft and rigid tissues—like muscle and bone—to produce biological systems capable of both robustness and strength. We present foundational, general-purpose pipelines to simulate and fabricate cable-driven soft-rigid robots with embedded skeletons. We show that robots built using these methods can fluidly mimic biological systems while achieving greater force output and external load resistance than purely soft robots. Finally, we show how our simulation and fabrication pipelines can be leveraged to create more complex robots and do model- based control. 

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