Library · Optimization & control
What Actuation & Robotic Control got wrong, from 16 theses
Summary written by a model from the records below: The records evaluate various actuation mechanisms, physical models, and control policies across soft robotics, aerial platforms, and dynamic robotic systems. They identify recurring failures stemming from mechanical hysteresis, dynamic instability under contact, model breakdown, efficiency limitations, and insufficient control authority. These records come from graduate theses, 2021 to 2026, each labeled with its degree where the repository states it, and each links to its thesis. They were extracted by language models reading the full text, so treat each as a lead to read, not a verdict.
Plus 10 problems the authors left open, listed at the end.
Failure modes, by theses reporting them
Select a mode to jump to its records.
Mechanical hysteresis, compliance, and internal coupling degrade soft and cable-driven actuation
Soft pneumatic chambers, flexible cables, and fabric reinforcements suffer from mechanical hysteresis, seam-induced asymmetric stiffness, and interference between actuation and sensing. These physical properties produce path misalignment between actuation cycles, unintended non-uniform bending, and an inability to independently observe and control joint trajectories.
Tried and failed
single-chamber simultaneous pneumatic actuation and sensing applied to soft robotic end-effectors. Reason: actuation pressure changes for shape-changing interfere with using the same cavity for tactile pressure sensing
A soft robotic approach for robot-assisted palpation training · Imperial · PhD
Tried and failed
kinematic pose tracking from tendon displacement applied to continuum robot position estimation. Reason: mechanical hysteresis caused path misalignment between forward and return actuation cycles
Forward-Viewing Ultrasound Guidance of a Robotically-Steered Guidewire for Peripheral Interventions · Georgia Tech · PhD
Tried and failed
fabric tube reinforced soft pneumatic actuators applied to burrowing soft robot propulsion. Reason: overlapping fabric seams created asymmetric stiffness causing unintended non-uniform bending during actuation
Micromechanics of passive and active inclusions in granular media · Georgia Tech · PhD
Considered and rejected
Considered and rejected: Rejected cable-driven piezoelectric ultrasonic motor mechanisms due to cable flexibility and hysteresis.
Image Guided High Precision Robotic Positioning in MRI for Medical Applications · Georgia Tech · PhD
Contact dynamics and unmodeled perturbations induce resonance and instability in feedback control
Passive impedance suppression, resonant vibration locomotion, and operational space controllers experience severe instability when subjected to non-rigid interfaces, surface defects, or contact impacts. These interactions cause phase shifts that amplify oscillations, produce stochastic heading drift, and generate large velocity error spikes.
Tried and failed
servomotor-based passive impedance tremor suppression applied to wearable wrist exoskeleton. Outcome: unstable. Reason: non-rigid interface contact dynamics caused phase shifts and resonance, amplifying tremor oscillations instead of suppressing them
Design and Control of an Ergonomic Wearable Full-Wrist Exoskeleton for Pathological Tremor Alleviation · Virginia Tech · Doctorate
Tried and failed
open-loop resonant vibration actuation for locomotion applied to microrobot trajectory steering. Outcome: unstable. Reason: minute surface defects and unlevelness caused stochastic heading drift and trajectory discontinuities
Sensing, actuation, and intelligence integration in micro-robotics · Georgia Tech · PhD
Tried and failed
operational space control without impact projection applied to bipedal running robot control. Outcome: unstable. Reason: severe underactuation and velocity error spikes from impact timing sensitivity
Controlling Contact Transitions for Dynamic Robots · Penn · PhD
Considered and rejected
Considered and rejected: Rejected cancelling expected motor commands at the actuator level rather than sensory signals because it exhibits internal instability under integral feedback and fails to prevent sensor saturation.
Bio-inspired robotics: efference copies and adaptive feedforward control · Imperial · PhD
Simplified aerodynamic surfaces and multirotor arrangements lack fault tolerance and control authority
Relying on standard alternating-direction multirotor configurations or single-surface pitch control results in lost yaw authority during motor failures and large vertical accelerations during gusts. Consequently, simpler quadcopter and elevator-only setups are rejected in favor of redundant multirotor layouts and active morphing to ensure control authority and lower vibration.
Tried and failed
standard alternating-direction multirotor propeller configuration applied to fault-tolerant hexacopter control. Outcome: unstable. Reason: loss of yaw control authority following single motor or processor failure
Optimization-based design of fault-tolerant avionics · Georgia Tech · PhD
Tried and failed
single-surface pitch control without coordinated dihedral actuation applied to high-frequency vertical gust rejection. Outcome: worse than baseline. Reason: elevator-only control yielded large vertical accelerations compared to combining pitch with active dihedral morphing
Multibody Dynamics of Aeromechanical Systems · Virginia Tech · Doctorate
Considered and rejected
Considered and rejected: Rejected quadcopter configuration in favor of hexacopter (hexa+) to ensure motor-failure redundancy, reduced vibration, and proper arm alignment with crop rows.
Design of an Innovative Spraying System for High Precision Aerial Dispersion in Vineyards · Politecnico di Torino · PhD
Linear and hyperelastic constitutive models break down under nonlinear operating regimes
Linear displacement formulations fail to predict robotic actuator positioning accurately due to direction-dependent actuation differences and nonlinear friction. Similarly, finite element analysis with hyperelastic material models experiences numerical instability and breakdown when subjected to high actuation pressures in soft continuum robots.
Tried and failed
linear displacement model for actuator positioning applied to robotic actuator displacement prediction. Outcome: worse than baseline. Reason: nonlinear friction and direction-dependent actuation differences caused severe prediction errors
Image Guided High Precision Robotic Positioning in MRI for Medical Applications · Georgia Tech · PhD
Tried and failed
finite element analysis with hyperelastic material models applied to pneumatic soft continuum robot grasping. Outcome: did not converge. Reason: numerical instability and breakdown of hyperelastic constitutive models under high actuation pressures
Modeling, Planning, and Learning for Soft Robots in Human-Centric, Contact-Rich Environments · Harvard · PhD
Soft and hydrogel actuators exhibit severe energy efficiency deficits
Soft motors achieve very low operational efficiency when compared to rigid motor baselines and commercial hard motors. In addition, porous sweating polyacrylamide hydrogel actuators suffer further decreases in actuation efficiency while actively thermoregulating.
Lost to a baseline
Soft motor efficiency of 0.24% to 0.35% was lower than simulated rigid equivalent motor (~70%) and commercial hard motors
The Design and Application of Soft Electromagnetic Actuators · Georgia Tech · PhD
Lost to a baseline
Porous sweating PAAm hydrogel actuators demonstrated lower actuation efficiency while actively sweating/thermoregulating.
THE SENSITIVE SOFT ROBOT FROM MULTIMODAL SKIN TO SELF-HEALING ADAPTIBILITY · Cornell · PhD
Unconstrained policy actions and latent activations degrade reinforcement learning motor execution
Residual policy learning without action regularization allows residual actions to become excessively large, degrading trajectory quality and preventing sim-to-real transfer. Similarly, directly activating latent representation units in biomechanical policies produces erratic dashes instead of structured discrete motor actions.
Tried and failed
residual policy learning without action regularization applied to robot motor skill composition. Outcome: did not generalise. Reason: unregularized residual actions grew excessively large, degrading trajectory quality and preventing sim-to-real transfer
Learning interactive robot behaviors using deep reinforcement learning · Georgia Tech · PhD
Tried and failed
latent unit activation for behavioral control applied to biomechanical reinforcement learning policy. Outcome: did not generalise. Reason: activating internal representation units yielded erratic dashes rather than structured discrete motor actions
Modeling the neural control of movement with a virtual rodent · Harvard · PhD
Left open by the authors
Problems the authors named and did not get to.
Left open
Deploy and validate the developed sampling-based Model Predictive Control (MPC) frameworks on real-world robotic hardware. Blocker: Requires access to physical robotic hardware systems and an experimental robotics lab setup.
Sampling-based Dynamic Optimization: Theory, Analysis and Applications · Georgia Tech · PhD
Left open
Test motor averaging versus performance-optimization on intermediate reaching movements under forced response times below 222ms using a robotic manipulandum setup. Blocker: Requires human subjects and experimental hardware (robotic manipulandum/vBOT reaching apparatus)
Understanding How Environmental Dynamics and Uncertainty Affect Adaptive Changes in Motor Planning · Harvard · PhD
Left open
Evaluate parallel trajectory planning performance on offloaded mobile robotics SLAM workloads and multi-robot physical testbeds. Blocker: Requires access to multiple physical manipulator robots and mobile robotic hardware setups
MATRIX: Manipulator Avoidance Trajectories via Reactive, Integrated eXtreme-scale computing · Queen's University · Master's
Left open
Train a neural network conditioned on previous robot states and actions to model real-world actuation noise for sim-to-real transfer. Blocker: Requires real robot hardware trajectory data to model real-world actuation dynamics.
Sim2Robot: Training Robots for the Real-World with Imperfect Simulators · Georgia Tech · PhD
Left open
Implement a rate-dependent or multi-axis vector Preisach hysteresis model parameterized across actuation speeds for soft robotic actuators. Blocker: Requires a physical soft actuator apparatus to collect multi-speed and multi-axis characterization data.
Mechanics of Soft-Rigid Interactions: From Wearable Robots to Stingray Skeletons · Harvard · PhD
Left open
Integrate selectively stiffening microchannels or dielectric elastomer actuators into elastomer domes to reprogram deflection directions for omnidirectional actuation. Blocker: Requires a physical soft robotics fabrication laboratory, specialized elastomer materials, and testing apparatus
Manufacturing and Design of Echinoderm-Inspired Underwater Soft Robots · Harvard · PhD
Left open
Integrate soft logic valves directly inside soft robot appendages to replace discrete solenoid valves for decentralized control. Blocker: Requires a physical soft robotics manufacturing and testing lab to fabricate and validate the soft logic valves and appendages.
Manufacturing and Design of Echinoderm-Inspired Underwater Soft Robots · Harvard · PhD
Left open
Incorporate embedded soft sensors directly into DEA-driven pump-valve structures for closed-loop fluidic feedback. Blocker: Requires soft robotics fabrication lab, dielectric elastomer actuators, elastomeric channels, and physical testing hardware
Sensing, Actuation, and Control of Soft Fluid-driven Robots by Liquid-elastomer Composite Sensors and Dielectric Elastomer Actuators · Harvard · PhD
Left open
Develop a soft robotic hand with an integrated 1-DOF mechanism to dynamically adjust digit arrangements on the fly. Blocker: Requires mechanical engineering hardware fabrication and a robotics lab to construct and test the physical soft gripper mechanism.
Design Principles for Improving Precision and Dexterity of Soft Robotic Hands · Harvard · PhD
Left open
Investigate dielectric elastomer actuators or electroactive polymers to replace pneumatic joint stiffening in soft flexure robotic joints. Blocker: Requires a physical materials/robotics lab and fabrication hardware to test dielectric elastomer actuators.
Characterization of Soft Structures for Synergy-Based Performance Optimization in Robotic Grasping and Other Manipulation Tasks · Georgia Tech · PhD
Who has worked on this
Authors of the public theses cited on this page, most-cited first.
- Daniel Enrique Martinez · Georgia Tech · PhD · 2024
Image Guided High Precision Robotic Positioning in MRI for Medical Applications - Michael Austin Bell · Harvard · PhD · 2021
Manufacturing and Design of Echinoderm-Inspired Underwater Soft Robots - Mohamed Ahmed Yehia Zakaria · Virginia Tech · Doctorate · 2026
Multibody Dynamics of Aeromechanical Systems - Kieran S. Lachmansingh · Queen's University · Master's · 2026
MATRIX: Manipulator Avoidance Trajectories via Reactive, Integrated eXtreme-scale computing - Benjamin Campbell · Imperial · PhD · 2025
Bio-inspired robotics: efference copies and adaptive feedforward control - Connor Michael McCann · Harvard · PhD · 2025
Mechanics of Soft-Rigid Interactions: From Wearable Robots to Stingray Skeletons - Zhijian Hao · Georgia Tech · PhD · 2024
Sensing, actuation, and intelligence integration in micro-robotics - Niranjan Kumar Kannabiran · Georgia Tech · PhD · 2024
Learning interactive robot behaviors using deep reinforcement learning - Noah Kohls · Georgia Tech · PhD · 2024
The Design and Application of Soft Electromagnetic Actuators - Diego Aldarondo · Harvard · PhD · 2024
Modeling the neural control of movement with a virtual rodent - Joanne Truong · Georgia Tech · PhD · 2024
Sim2Robot: Training Robots for the Real-World with Imperfect Simulators - William Yang · Penn · PhD · 2024
Controlling Contact Transitions for Dynamic Robots
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