About

Nicholas Gravish is an Associate Professor in the Mechanical & Aerospace Engineering department at UC San Diego. His research focuses on movement dynamics in biology and robotics, driven by the development of new methods for analyzing and generating locomotion. He employs tools from robotics, computer vision, and physics to advance understanding and innovation in these areas. Gravish completed his postdoctoral scholarship at Harvard University from 2013 to 2016, working in the School of Engineering & Applied Sciences and the Department of Organismic and Evolutionary Biology under advisers Robert J. Wood and Stacey A. Combes. He earned his Ph.D. in Physics at Georgia Tech between 2008 and 2013, where his thesis investigated the collective dynamics of active and passive granular media, with a minor in mechanics of materials, advised by Daniel I. Goldman. He holds a B.S. in Physics from UC Santa Barbara, awarded in 2005, where he also received undergraduate research honors in 2004 and 2005.

Research topics

• Computer Science
• Artificial Intelligence
• Engineering
• Physics
• Medicine
• Geography
• Civil engineering
• Materials science
• Cartography
• Mathematics
• Geotechnical engineering
• Geometry
• Structural engineering
• Physical medicine and rehabilitation
• Simulation
• Mechanical engineering

Selected publications

• Limb Compliance for Underactuated Propulsion in Resistive Media

  2026-04-07

  articleSenior author
  PublisherDOI

• Opportunities for Soft Electrohydraulic Actuation for Burrowing in Dry and Submerged Granular Media

  2026-04-07

  article

  Development of robotic platforms capable of burrowing in granular media (GM) has shown potential for applications in agriculture, construction of infrastructure, and extraterrestrial exploration. A promising strategy for burrowing is the use of high-frequency vibration to locally fluidize the GM to reduce drag forces. However, there have been few implementations of this method for robotic burrowers. In this work, we explore the use of hydraulically amplified, self-healing electrostatic (HASEL) actuators for soft robots capable of burrowing in dry and submerged GM. We propose that HASEL actuators can achieve both high-frequency vibration to fluidize GM and low-frequency, high-strain actuation for effective burrowing. We present a prototype multi-segmented robot design using HASEL actuators. We evaluate the drag reduction effects of high-frequency HASEL actuation in GM, and investigate the locomotion properties of the multi-segmented robots on the surface of, and burrowing inside, GM. We also demonstrate the capability of our actuators to detect obstacles within GM, and analyze the power consumption and operational endurance of our system. This work opens up opportunities for the future use of HASEL actuators for soft burrowing robots.

  PublisherDOI

• Multi-Functional Granular Propulsion: Bio-Inspired Orientation Control and Local Fluidization for Crawl-To-Dig Transitions

  2025-10-19

  articleSenior author

  Existing robots designed for locomotion in granular media typically excel at a single purpose—either surface travel or subsurface digging—while lacking the ability to perform both within the same platform. In contrast, nature offers various examples of burrowing organisms that exhibit multi-functional digging behaviors by separating their body into two essential parts: a digger for substrate intrusion and rest of the body as anchor for stabilization and controlling digger orientation. Inspired by these biological strategies, we present an extension to an existing Screw Propelled Vehicle (SPV) that incorporates an adjustable body anchor to reduce drag and enable orientation control. This integration allows the robot to transition between horizontal crawling and vertical digging. We also investigate the effect of local fluidization (LF), a bio-inspired technique that temporarily reduces the resistive forces in granular media. Experimental results show that integrating LF improves surface propulsion performance in terms of speed and depth with increment of over 5x compared to the baseline configuration. These findings support the hypothesis that bio-inspired design principles—specifically body–anchor separation and local fluidization—significantly enhance both the functionality and efficiency of granular locomotion robots, providing a pathway toward more versatile, autonomous, and high-performance subsurface exploration.

  PublisherDOI

• Autonomous Burrowing and Retrieval of Soft Robotic Anchors in Granular Media

  2025-04-22 · 2 citations

  articleSenior author

  Vertical digging into and out of granular media is a challenging task for autonomous systems. Granular media present considerable resistance to vertical penetration due to the high friction forces and large pressure at depths. In this paper, we present a soft robot that is capable of digging into and out of granular media to depths over 10× its body length. Our robot incorporates a vibration motor to locally fluidize the granular media for burrowing, and a soft pneumatic actuator to adjust the volume and hence the density of the robot, allowing it to transition from digging down to digging up. To analyze the performance of the robot, we measure its weight and density, track its location using a motion capture system, and investigate the effect of local fluidization. When the robot is buried and inflated with vibration turned off, it can increase its passive anchoring force by 5.22× (up to 35 N) relative to when the robot is deflated with vibration on. By contrast, by inflating the soft pneumatic bladder and providing vibration the robot is able to actively unburrow.

  PublisherDOI

• Burrowing and unburrowing in submerged granular media through fluidization and shape-change

  Frontiers in Robotics and AI · 2025-07-31 · 1 citations

  articleOpen access

  Subterranean exploration in submerged granular media (GM) presents significant challenges for robotic systems due to high drag forces and the complex physics of GM. This paper introduces a robotic system that combines water-jet-based fluidization for self-burrowing in submerged environments and an untethered, volume-change mechanism for burrowing out. The water-based fluidization approach significantly reduces drag on the robot, allowing it to burrow into GM with minimal force. To burrow out, the robot uses a soft, inflatable bladder that undergoes periodic radial expansion, inspired by natural systems such as razor clams. Experimental results demonstrate that increased water flow rates accelerate the burrowing process, while the unburrowing mechanism is effective at varying depths. Comparisons between pneumatic and hydraulic untethered systems highlight trade-offs in terms of operational time and unburrowing speed. This work advances the capabilities of robots in underwater environments, with potential applications in environmental monitoring and underwater archaeology.

  PublisherOA PDFDOI

• Active contacts create controllable friction

  ArXiv.org · 2025-01-16

  preprintOpen accessSenior author

  Sliding friction between two dry surfaces is reasonably described by the speed-independent Amonton-Coulomb friction force law. However, there are many situations where the frictional contact points between two surfaces are "active" and may not all be moving at the same relative speed. In this work we study the sliding friction properties of a system with multiple active contacts each with independent and controllable speed. We demonstrate that multiple active contacts can produce controllable speed-dependent sliding friction forces, despite each individual contact exhibiting a speed-independent friction. We study in experiment a rotating carousel with ten speed-controlled wheels in frictional contact with the ground. We first vary the contact speeds and demonstrate that the equilibrium system speed is the median of the active contact speeds. Next we directly measure the ground reaction forces and observe how the contact speeds can control the force-speed curve of the system. In the final experiments we demonstrate how control of the force-speed curve can create sliding friction with a controllable effective viscosity and controllable sliding friction coefficient. Surprisingly, we are able to demonstrate that frictional contacts can create near frictionless sliding with appropriate force-speed control. By revealing how active contacts can shape the force-speed behavior of dry sliding friction systems we can better understand animal and robot locomotion, and furthermore open up opportunities for new engineered surfaces to control sliding friction.

  PublisherOA PDFDOI

• Grasping and rolling in-plane manipulation using deployable tape spring appendages

  Science Advances · 2025-04-09 · 5 citations

  articleOpen accessSenior authorCorresponding

  Rigid robot arms face a tradeoff between their overall reach distance and how compactly they can be collapsed. However, the tradeoff between long reach and small storage volume can be resolved using deployable structures such as tape springs. We developed bidirectional tape spring "fingers" that have large buckling strength compared to single tape springs and that can be spooled into a compact state or unspooled to manipulate objects. We integrate fingers into a robot manipulator that allows for object Grasping and Rolling In Planar configurations (called GRIP-tape). The continuum kinematics of the fingers enables a multitude of manipulation capabilities such as translation, rotation, twisting, and multi-object conveyance. Furthermore, the dual mechanical properties of stiffness and softness in the fingers endow the gripper with inherent safety from collisions and enables soft-contact with objects. Deployable structures such as tape springs offer opportunities for manipulation in cluttered or remote environments.

  PublisherDOI

• Active contacts control sliding friction

  Proceedings of the National Academy of Sciences · 2025-07-09

  articleOpen accessSenior authorCorresponding

  Sliding friction between two dry surfaces is commonly described by the speed-independent Amonton-Coulomb friction force law. However, there are many situations where multiple frictional contact points between two surfaces are "active" and each can move at a different relative speed. Here, we study the sliding friction properties of a system with multiple active contacts each with independent and controllable speed. We demonstrate that multiple active contacts can produce controllable speed-dependent sliding friction forces, despite each individual contact exhibiting a speed-independent friction. We study in experiment a rotating carousel with ten speed-controlled wheels in frictional contact with the ground. We first vary the contact speeds and demonstrate that the equilibrium system speed is the median of the active contact speeds. Next we directly measure the sliding friction forces and observe how the contact speeds can control the force-speed curve of the system. In the final experiments, we demonstrate how control of the force-speed curve can create sliding friction with a controllable effective viscosity and controllable sliding friction coefficient. Surprisingly, we are able to demonstrate that frictional contacts can create near frictionless sliding with appropriate force-speed control. By revealing how active contacts can shape the force-speed behavior of dry sliding friction systems, we can better understand animal and robot locomotion and furthermore open up opportunities for new engineered surfaces to control sliding friction.

  PublisherDOI

• Supra-resonant wingbeats in insects

  bioRxiv (Cold Spring Harbor Laboratory) · 2025-05-11 · 1 citations

  preprintOpen access

  Abstract Powering small-scale flapping flight is challenging, yet insects sustain exceptionally fast wingbeats with ease. Since insects act as tiny biomechanical resonators, tuning their wingbeat frequency to the resonant frequency of their springy thorax and wings could make them more efficient fliers. But operating at resonance poses control problems and potentially constrains wingbeat frequencies within and across species. Resonance may be particularly limiting for the many orders of insects that power flight with specialized muscles that activate in response to mechanical stretch. Here, we test whether insects operate at their resonant frequency. First, we extensively characterize bumblebees and find that they surprisingly flap well above their resonant frequency via interactions between stretch-activation and mechanical resonance. Modeling and robophysical experiments then show that resonance is actually a lower bound for rapid wingbeats in most insects because muscles only pull, not push. Supra-resonance emerges as a general principle of high-frequency flight across five orders of insects from moths to flies.

  PublisherOA PDFDOI

• Energetic and Control Trade-offs in Spring-Wing Systems

  arXiv (Cornell University) · 2024-03-06 · 3 citations

  preprintOpen accessSenior author

  Flying insects are thought to achieve energy-efficient flapping flight by storing and releasing elastic energy in their muscles, tendons, and thorax. However, flight systems consisting elastic elements coupled to nonlinear, unsteady aerodynamic forces also present possible challenges to generating steady and responsive wing motions. In previous work, we examined the resonance properties of a dynamically-scaled robophysical system consisting of a rigid wing actuated by a motor in series with a spring, which we call a spring-wing system \cite{Lynch2021-ri}. In this paper, we seek to better understand the effects of perturbations on resonant systems via a non-dimensional parameter, the Weis-Fogh number. We drive a spring-wing system at a fixed resonant frequency and study the response to an internal control perturbation and an external aerodynamic perturbation with varying Weis-Fogh number. In our first experiments, we provide a step change in the input forcing amplitude and study the wing motion response. In our second experiments we provide an external fluid flow directed at the flapping wing and study the perturbed steady-state wing motion. We evaluate results across the Weis-Fogh number, which describes the ratio of inertial and aerodynamic forces and the potential energetic benefits of elastic resonance. The results suggest that spring-wing systems designed for maximum energetic efficiency also experience trade-offs in agility and stability as the Weis-Fogh number increases. Our results demonstrate that energetic efficiency and wing maneuverability are in conflict in resonant spring-wing systems suggesting that mechanical resonance presents tradeoffs in insect flight.

  PublisherOA PDFDOI

Recent grants

• EFRI C3 SoRo: Control of Local Curvature and Buckling for Multifunctional Textile-Based Robots

  NSF · $2.0M · 2019–2024

• EAGER: Modeling the Interaction Physics between Soft-structures and Granular Materials

  NSF · $125k · 2018–2019

Frequent coauthors

• Daniel I. Goldman

  35 shared

• Wei Zhou

  University of Arizona

  34 shared

• Simon Sponberg

  Georgia Institute of Technology

  23 shared

• James Lynch

  University of California, San Diego

  19 shared

• Michael T. Tolley

  University of California, San Diego

  19 shared

• Kellar Autumn

  Lewis & Clark College

  16 shared

• Stacey A. Combes

  University of California, Davis

  13 shared

• Tetsuo Yamaguchi

  13 shared

Labs

• Gravish labPI

  Movement dynamics in biology and robotics

Education

• Ph.D., Mechanical Engineering

  Georgia Tech

• B.S.

  University of California, Santa Barbara

Awards & honors

• James S. McDonnell postdoctoral fellowship