# Publications

2019
A. De, A. Stewart-Height, and D. E. Koditschek, “Task-Based Control and Design of a BLDC Actuator for Robotics,” RAL, pp. 8, 2019. Publisher's VersionAbstract
This paper proposes a new multi-input brushless DC motor current control policy aimed at robotics applications. The controller achieves empirical improvements in steady-state torque and power-production abilities relative to conventional controllers, while retaining similarly good torquetracking and stability characteristics. Simulations show that non-conventional motor design optimizations whose feasibility is established by scaling model extrapolations from existing motor catalogues can vastly amplify the effectiveness of this new control-strategy.
2018
A. Shamsah, A. De, and D. E. Koditschek, “Analytically-Guided Design of a Tailed Bipedal Hopping Robot”. IEEE, pp. 2237–2244, 2018. Publisher's Version
A. De and D. E. Koditschek, “Averaged anchoring of decoupled templates in a tail-energized monoped,” in Robotics Research, Springer, 2018, pp. 269–285.
A. De, S. A. Burden, and D. E. Koditschek, “A hybrid dynamical extension of averaging and its application to the analysis of legged gait stability,” The International Journal of Robotics Research, vol. 37, no. 2-3, pp. 266-286, 2018. Publisher's VersionAbstract
We extend a smooth dynamical systems averaging technique to a class of hybrid systems with a limit cycle that is particularly relevant to the synthesis of stable legged gaits. After introducing a definition of hybrid averageability sufficient to recover the classical result, we illustrate its applicability by analysis of first a one-legged and then a two-legged hopping model. These abstract systems prepare the ground for the analysis of a significantly more complicated two legged model: a new template for quadrupedal running to be analyzed and implemented on a physical robot in a companion paper. We conclude with some rather more speculative remarks concerning the prospects for further extension and generalization of these ideas.
A. De and D. E. Koditschek, “Vertical hopper compositions for preflexive and feedback-stabilized quadrupedal bounding, pacing, pronking, and trotting,” The International Journal of Robotics Research, vol. 37, no. 7, pp. 743-778, 2018. Publisher's VersionAbstract
This paper applies an extension of classical averaging methods to hybrid dynamical systems, thereby achieving formally specified, physically effective and robust instances of all virtual bipedal gaits on a quadrupedal robot. Gait specification takes the form of a three parameter family of coupling rules mathematically shown to stabilize limit cycles in a low degree of freedom template: an abstracted pair of vertical hoppers whose relative phase locking encodes the desired physical leg patterns. These coupling rules produce the desired gaits when appropriately applied to the physical robot. The formal analysis reveals a distinct set of morphological regimes determined by the distribution of the body’s inertia within which particular phase relationships are naturally locked with no need for feedback stabilization (or, if undesired, must be countermanded by the appropriate feedback), and these regimes are shown empirically to analogously govern the physical machine as well. In addition to the mathematical stability analysis and data from physical experiments we summarize a number of extensive numerical studies that explore the relationship between the simple template and its more complicated anchoring body models.
2017
A. De, “Modular Hopping and Running via Parallel Composition,” University of Pennsylvania, 2017. Publisher's VersionAbstract
Though multi-functional robot hardware has been created, the complexity in its functionality has been constrained by a lack of algorithms that appropriately manage flexible and autonomous reconfiguration of interconnections to physical and behavioral components.Raibert pioneered a paradigm for the synthesis of planar hopping using a composition of parts'': controlled vertical hopping, controlled forward speed, and controlled body attitude. Such reduced degree-of-freedom compositions also seem to appear in running animals across several orders of magnitude of scale. Dynamical systems theory can offer a formal representation of such reductions in terms of anchored templates,'' respecting which Raibert's empirical synthesis (and the animals' empirical performance) can be posed as a parallel composition. However, the orthodox notion (attracting invariant submanifold with restriction dynamics conjugate to a template system) has only been formally synthesized in a few isolated instances in engineering (juggling, brachiating, hexapedal running robots, etc.) and formally observed in biology only in similarly limited contexts.In order to bring Raibert's 1980's work into the 21st century and out of the laboratory, we design a new family of one-, two-, and four-legged robots with high power density, transparency, and control bandwidth. On these platforms, we demonstrate a growing collection of $\{$body, behavior$\}$ pairs that successfully embody dynamical running / hopping gaits'' specified using compositions of a few templates, with few parameters and a great deal of empirical robustness. We aim for and report substantial advances toward a formal notion of parallel composition---embodied behaviors that are correct by design even in the presence of nefarious coupling and perturbation---using a new analytical tool (hybrid dynamical averaging).With ideas of verifiable behavioral modularity and a firm understanding of the hardware tools required to implement them, we are closer to identifying the components required to flexibly program the exchange of work between machines and their environment. Knowing how to combine and sequence stable basins to solve arbitrarily complex tasks will result in improved foundations for robotics as it goes from ad-hoc practice to science (with predictive theories) in the next few decades.
V. Vasilopoulos, O. Arslan, A. De, and D. E. Koditschek, “Sensor-based legged robot homing using range-only target localization”. IEEE, pp. 2630–2637, 2017.
2016
G. Kenneally, A. De, and D. E. Koditschek, “Design Principles for a Family of Direct-Drive Legged Robots,” IEEE Robotics and Automation Letters, vol. 1, no. 2, pp. 900-907, 2016.
G. Wenger, A. De, and D. E. Koditschek, “Frontal plane stabilization and hopping with a 2DOF tail”. IEEE, pp. 567–573, 2016. Publisher's Version
T. T. Topping, V. Vasilopoulos, A. De, and D. E. Koditschek, “Towards bipedal behavior on a quadrupedal platform using optimal control”. pp. 98370H, 2016. Publisher's Version
2015
A. De and D. E. Koditschek, “Parallel composition of templates for tail-energized planar hopping”. IEEE, pp. 4562–4569, 2015. Publisher's Version
A. De and D. E. Koditschek, The Penn Jerboa: A Platform for Exploring Parallel Composition of Templates. 2015. Publisher's Version
A. L. Brill, A. De, A. M. Johnson, and D. E. Koditschek, “Tail-assisted rigid and compliant legged leaping”. IEEE, pp. 6304–6311, 2015.
2014
A. De, K. S. Bayer, and D. E. Koditschek, “Active sensing for dynamic, non-holonomic, robust visual servoing”. IEEE, pp. 6192–6198, 2014. Publisher's Version
A. De and D. E. Koditschek, Parallel Composition of Templates for Planar Hopping - Technical Report. University Of Pennsylvania, 2014.
2013
A. De, A. Ribeiro, W. Moran, and D. E. Koditschek, “Convergence of Bayesian histogram filters for location estimation”. IEEE, pp. 7047–7053, 2013.
M. M. Ankarali, H. T. Sen, A. De, A. M. Okamura, and N. Cowan, “Haptic Feedback Enhances Rhythmic Motor Control By Reducing Variability, Not Convergence Rate,” Journal of Neurophysiology, pp. jn.00140.2013, 2013. Publisher's VersionAbstract
Stability and performance during rhythmic motor behaviors such as locomotion are critical for survival across taxa: falling down would bode well for neither cheetah nor gazelle. Little is known about how haptic feedback, particularly during discrete events such as the heel-strike event during walking, enhances rhythmic behavior. To determine the effect of haptic cues on rhythmic motor performance, we investigated a virtual paddle juggling behavior, analogous to bouncing a table tennis ball on a paddle. Here, we show that a force impulse to the hand at the moment of ball-paddle collision categorically improves performance over visual feedback alone, not by regulating the rate of convergence to steady state (e.g. via higher gain feedback or modifying the steady-state hand motion), but rather by reducing cycle-to-cycle variability. This suggests that the timing and state cues afforded by haptic feedback decreases the nervous system's uncertainty of the ball's state to enable more accurate control, but that the feedback gain itself is unaltered. This decrease in variability leads to a substantial increase in the mean first passage time, a measure of the long-term metastability of a stochastic dynamical system. Rhythmic tasks such as locomotion and juggling involve intermittent contact with the environment (i.e. hybrid transitions), and the timing of such transitions is generally easy to sense via haptic feedback. This timing information may improve metastability, equating to less frequent falls or other failures depending on the task.
A. De and D. E. Koditschek, “Toward dynamical sensor management for reactive wall-following”. IEEE, pp. 2400–2406, 2013.
2011
A. De, G. Lynch, A. Johnson, and D. Koditschek, “Motor sizing for legged robots using dynamic task specification,” 2011 IEEE Conference on Technologies for Practical Robot Applications (TePRA). pp. 64 -69, 2011.Abstract
We explore an approach to incorporating task and motor thermal dynamics in the selection of actuators for legged robots, using both analytical and simulation methods. We develop a motor model with a thermal component and apply it to a vertical climbing task; in the process, we optimally choose gear ratio and therefore eliminate it as a design parameter. This approach permits an analytical proof that continuous operation yields superior thermal performance to intermittent operation. We compare the results of motor sizing using our proposed method with more conventional techniques such as using the continuously permissible current specification. Our simulations are run across a database of commercially available motors, and we envision that our results might be of immediate use to robot designers for motor as well as gearbox selection.
2010
A. De, “Neuromechanical Control of Paddle Juggling,” Johns Hopkins University, 2010.