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Here are the robotics projects I have worked on in grad school:
Underactuated appendage driven robot for swimming and sensing in granular environments
Designed compliant/underactuated robotic mechanisms for granular and underwater environments; built constrained assemblies and iterated via quantitative experiments. Untethered robot was able to swim and sense obstacles in beach sand. It was the fastest untethered digging and sensing robot at the time.
What I did:
Designed underactuated appendages to generate propulsive thrust in granular media.
Added “terrafoils” to modulate lift and maintain subsurface depth during locomotion.
Demonstrated obstacle sensing via appendage force changes during swimming under sand.
First demonstration of burrowing robot on the beach in San Diego - fastest robot at the time
Toward Robotic Sensing and Swimming in Granular Environments using Underactuated Appendages. S Chopra, D Vasile, S Jadhav, M Tolley, N Gravish. Advanced Intelligent Systems. 2023. PDF
Tags: Robotics • Mechanism Design • Underactuated/Compliant Systems • Experimentation • Sensing Integration
Adaptive Granular Jamming feet for Robot Locomotion on sand
This work is about a soft robotic foot that passively changes shape on impact and actively changes stiffness using granular jamming to improve locomotion on sand. The work measures impact acceleration, penetration depth, shear traction, and pullout force across foot states, showing substantial reductions in impact deceleration, penetration depth, and pullout force relative to rigid feet.
What I did:
Designed a granular‑jamming foot with an airtight membrane and selectable granular fill; studied how material choice affects stiffness under load.
Built a fluidized granular bed test platform and ran drop, shear, and pullout experiments across multiple “foot state” conditions.
Quantified performance using accelerometry + high‑speed imaging + load cell measurements to link foot state to locomotion‑relevant metrics.
Granular Jamming Feet Enable Improved Foot-Ground Interactions for Robot Mobility on Deformable Ground. S Chopra, M Tolley, N Gravish. IEEE Robotics and Automation Letters. 2020. PDF
Tags: Soft Robotics • Granular Jamming • Foot–Ground Interaction • Deformable Terrain • Experimental Validation
Anisotropic friction enabled Soft Digging Robot
A pneumatically actuated, worm‑inspired soft robot uses reciprocal elongation/contraction and anisotropic friction features (setae‑inspired elements + “terrafoils”) to dig through granular material. The robot uses four air‑powered longitudinal muscles and demonstrates forward digging under granular media and controlled steering/turning on the surface
What I did (work elements described in the paper)
Designed a worm‑inspired robot architecture using longitudinal pneumatic muscles and directional friction features to generate net forward motion.
Studied terrafoil angle tradeoffs (lift vs drag) and setae angle effects (anisotropic friction) using controlled drag/lift experiments.
Demonstrated forward digging and turning behavior via chamber actuation sequences and measured resulting motion/deflection outcomes
Drotman, D., Chopra, S., Gravish, N. and Tolley, M.T., 2022, April. Anisotropic forces for a worm-inspired digging robot. In 2022 IEEE 5th international conference on soft robotics (RoboSoft) (pp. 261-266). IEEE. PDF link
Tags: Soft Robotics • Granular Jamming • Foot–Ground Interaction • Deformable Terrain • Experimental Validation
Developed closed loop actuation for Robobee using embedded sensors
Developed closed loop actuation for Robobee using embedded sensors
Used laminate based techniques to make robobee sized robot based on the Harvard Robo-Bee. Everything from piezoelectric actuators, wings, transmission and body chassis was made in house using UV laser cutter with 10 micron precision.
I integrated the strain based sensing actuators on this robot and used a simple PD controller developed in Labview for strain based actuation for full feedback control.
Tags: Piezo Actuators • Embedded Sensing • SCM Fabrication • Micro‑Robotics • Signal Conditioning • Experimental Validation
High Speed video of testing for sensing of fluid surface contact during flight
Embedded sensors to enable on‑board sensing for micro‑robotic applications
I invented a piezoelectric bending actuator with integrated strain‑sensing regions fabricated using Smart Composite Microstructure (SCM) processes. The sensing regions measure actuator deflection via the piezoelectric effect, showing a linear relationship between sensor output and displacement over a wide range of voltages/frequencies, and demonstrating detection of wing collisions and wing degradation in micro-robotic flight contexts.
What I did (work elements described in the paper)
Designed an actuator architecture with electrically isolated sensing strips mechanically coupled to actuation layers; validated decoupling via geometry (gap) and layer design.
Implemented SCM fabrication steps (laser micromachining + lamination) and created a repeatable test setup with displacement sensing and signal conditioning.
Demonstrated sensing utility through wing collision and wing degradation experiments in microrobotic actuation contexts.
Piezoelectric actuators with on-board sensing for micro-robotic applications. S Chopra, N Gravish. Smart Materials and Structures. 2019. Pdf
Tags: Piezo Actuators • Embedded Sensing • SCM Fabrication • Micro‑Robotics • Signal Conditioning • Experimental Validation
Soft Appendages generating thrust in granular media using assymetry and mechanical compliance
This study showed how different parameters such as amplitude of input torque and stiffness of the appendage affect the propulsion of a model soft appendage in granular media. A hybrid (soft +stiff) appendage was designed for this study. To support these experiments, we proposed a modification to Resistive Force Theory (RFT) to enable it’s application to soft appendages.
Mechanical and actuation asymmetry in soft appendages leads to robotic propulsion in granular media. S Chopra, S Jadhav, MT Tolley, N Gravish. Adaptive Motion in Animals and Machines. 2021. . Pdf Poster
Tags: Soft Robotics • Actuation • Underactuated Robots • Experimental Validation
Phase change in a low boiling point liquid enables a soft digging robot
For this study, we were interested in appendage enabled digging in robots inspired by digging in turtles, mole crickets and moles. We present an actuation technique where a digging robot was powered by a self contained phase-change actuation system using two appendages.
We used Liquid coolants as low boiling point fluid (37degC). The design has small form factor compared to bulky electromechanical systems
Poster PDF
Tags: Soft Robotics • Actuation • Underactuated Robots • Experimental Validation
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