Soft Robotics Toolkit: Design Fabrication Modeling & Control

Elastomers are viscoelastic polymer materials that exhibit both elastic and viscous properties, allowing them to stretch significantly and return to their original shape without permanent deformation; they achieve this unique flexibility through minimal cross-linking between polymer chains, distinguishing them from other polymers like thermoplastics which lack significant cross-linking and thermosets which have extensive cross-linking that limits mobility.

Viscoelasticity is a material behavior combining elastic and viscous properties. Elastic solids deform and recover (Hooke's Law), while viscous fluids deform without recovery (Newton's Law). Viscoelastic materials recover only part of deformation, with behavior shifting from elastic at low temperatures to viscous at high temperatures. Four key properties reveal viscoelasticity: creep (continuous deformation under constant load), stress relaxation (decreasing stress under constant deformation), cyclic loading (hysteresis loop indicating energy dissipation), and strain rate dependence. Common examples include memory foam, gels, gelatin, and silicone putty. NASA developed flexible polyurethane viscoelastic materials for pressure relief applications.

Viscoelastic materials exhibit both elastic and viscous responses simultaneously. Elastic materials follow Hooke's law (ε = σ/E) while viscous materials follow Newton's law (dε/dt = σ/η). True viscoelastic materials show instantaneous deformation followed by continuous deformation under load, with partial recovery upon unloading and some permanent set. This behavior is typical of polymers like bitumen. Understanding these fundamental principles enables proper characterization through transient experiments (creep and relaxation tests) and dynamic oscillatory methods.

This video introduces fundamental concepts in material science, focusing on three key categories of material behavior under stress: elastic, unelastic (plastic), and viscoelastic. Elastic materials return to their original shape after deformation when the applied force is removed, demonstrating reversible deformation. Unelastic or plastic materials undergo permanent deformation where the material does not fully recover its original dimensions. Viscoelastic materials exhibit time-dependent behavior, showing characteristics of both elasticity and viscosity—deforming gradually under constant load and recovering slowly when the load is removed. Understanding these behaviors is essential for selecting appropriate materials in engineering applications, as each category responds differently to mechanical stress and environmental conditions.

Viscoelastic behavior represents a combination of elastic and viscous properties in materials under applied stress. A viscoelastic material exhibits both instantaneous elastic response and time-dependent viscous flow, meaning it partially returns to its original shape but also undergoes permanent deformation over time. This behavior combines solid-like elastic and liquid-like viscous properties. The response to stress depends on loading rate: faster loading results in more elastic behavior, while slower loading leads to more viscous behavior. Key phenomena include creep (gradual deformation under constant stress) and stress relaxation (gradual decrease in stress under constant strain). These materials can be modeled using Maxwell, Kelvin-Voigt, and standard linear models. Common examples include polymers, biological tissues, and glass. A practical application is memory foam mattresses, which gradually recover their shape after deformation.

A control system is an arrangement of components that performs a specific task by transforming input through a process to produce output; it can be classified into open loop systems (which operate without feedback and assume output meets requirements) or closed loop systems (which use feedback to automatically adjust and maintain desired output).

Control systems are classified as open-loop or closed-loop based on feedback presence. Open-loop systems follow a sequential chain: Controller → Amplifier → Actuator → Plant, with no feedback path. The timer-controlled lamp example demonstrates this: a 555 timer generates timing pulses, a transistor amplifies the signal, and a relay activates the lamp for a predetermined duration. These systems are simple and cost-effective but cannot compensate for disturbances or errors once they occur. Closed-loop systems add a feedback path: Plant output connects back to the summing point via Sensor → Transducer → Signal Conditioning. The error signal (reference minus actual) drives the controller. Robotic manipulators demonstrate closed-loop principles with continuous sensing and comparison. Closed-loop systems continuously monitor output and adjust control actions in real-time, providing inherent immunity to disturbances and ensuring accurate tracking of reference inputs.

Control systems are combinations of physical components arranged to produce proper output for a given reference input, and they are classified into two main types: Open Loop Control Systems, where the control action depends only on the input signal and not on the output, and Closed Loop Control Systems, where the control action depends on both the input signal and the output through a feedback path. Feedback is further divided into Positive Feedback, where the feedback signal is added to the input signal, and Negative Feedback, where the feedback signal is subtracted from the input signal.

A control system is a type of system that produces desired output by controlling its input, distinguishing it from a normal system which simply transforms input to output; control systems are categorized into two main types: open loop control systems, which operate without feedback and directly generate control signals to produce output, and closed loop control systems, which incorporate a feedback path that measures the actual output, compares it with the desired input at a mixer to generate an error signal, and automatically adjusts the control signal to achieve the desired output.

An Open Loop Control System is a system without feedback where the output does not affect the control action. A Closed Loop Control System is a system with feedback where the output is measured and fed back to compare with the desired input, allowing the system to correct errors automatically. Negative Feedback Systems are the most commonly used feedback configuration, where the feedback signal is subtracted from the input signal to reduce error and improve stability.

CAD (Computer-Aided Design) is the digital equivalent of manual drawing, enabling precise dimension specification and manufacturing preparation. Two fundamental manufacturing types exist: additive manufacturing (3D printing) builds objects layer by layer, while subtractive manufacturing (CNC machining) removes material from solid blocks. Popular CAD software includes Fusion 360 (free for students), SolidWorks, and FreeCAD. Mouse navigation controls include scroll wheel for zoom/rotation, middle button for rotation, and right button for panning. Standard views include Home (isometric), Front, Right, and Top views. Before 3D modeling, designers must master 2D sketching, selecting appropriate sketch planes (Front, Right, Top) based on design perspective. Primitive shapes (cubes, cylinders, triangles) serve as foundational building blocks. The origin point provides a reference coordinate system. Dimensioning uses the dimension tool to specify exact measurements. Converting 2D sketches to 3D requires understanding extrusion (extending profiles along an axis) and revolve (rotating sketches around an axis). The fillet tool creates rounded edges for manufacturability. Design flexibility is key—multiple approaches can achieve identical outcomes as long as dimensions are correct.

SolidWorks is a Computer-Aided Design (CAD) software that enables users to design equipment, perform simulations, and conduct strength analysis. The software provides three default templates: Part (3D single or multi-body parts), Assembly (combining multiple parts with mechanisms and motion studies), and Drawing (production representations). The Novice system restricts users to default templates, while Advanced mode allows custom template creation. The 3D modeling workflow involves: (1) Creating 2D sketches using basic geometric shapes on reference planes, (2) Defining dimensions and establishing geometric relationships between elements (blue indicates undefined, black indicates fully defined), (3) Converting 2D sketches to 3D objects using Extrude Base (adds material) or Extruded Cut (removes material), (4) Using Hole Wizard for uniform holes or Extruded Cut for irregular shapes. This foundational knowledge prepares learners for the structured tutorial series covering basic to professional CAD skills.

This comprehensive lesson covers the complete workflow for 3D CAD modeling. First, master 2D CAD commands as 3D builds upon 2D skills. Extract five essential icons: Solid Editing, Surface Editing, Modeling, Visual Styles, and View. Learn two methods for joining broken lines: JOIN for closed shapes and UNION for partially connected objects. Switch to South-East view for 3D operations. Use EXTRUDE command to create 3D objects from joined 2D profiles, specifying height. Understand the difference between Solid Extrusion (filled objects) and Surface Extrusion (hollow/mesh-like). Switch to Visual Styles to see actual 3D forms. This foundational workflow prepares students for advanced operations like union, difference, and intersection.

CAD (Computer-Aided Design) is the use of computer software for creating, modifying, and optimizing designs. Major CAD programs include Autodesk 3ds Max (popular 3D modeling and animation), Blender (open-source 3D modeling with game engine), AutoCAD (30+ years of development, 2D/3D capabilities), Autodesk Maya (3D design for advertising, gaming, film), SolidWorks (3D modeling and optimization for engineering sectors), CATIA (transportation design for automotive, aerospace, shipbuilding), and SketchUp (accessible 3D modeling for architects and designers). Each program serves specific industry needs, from professional engineering to educational purposes.

Computer-Aided Design (CAD) is a method for creating designs of products or objects using computer software. CAD enables designers to create both 2D and 3D representations. The technology is widely used in mechanical engineering, architecture, civil engineering, and graphic design. Key CAD software includes AutoCAD for product design and architectural drawings, SolidWorks for 3D modeling, and Adobe Illustrator for graphic design and logo creation. 3D modeling allows designers to create complex objects with realistic appearances. 3D drawing represents objects using length, width, and height measurements across X, Y, and Z axes. CAD software provides various drawing tools for creating circles, curved lines, text labels, hexagons, rectangles, and circles, along with dimensioning tools for adding measurements.

Fluidic soft actuators are limited by mass transport requirements - moving fluid into chambers to cause actuation, typically achieving 2-10 Hz. This is slower than field-driven actuators (dielectric elastomers) which respond almost instantaneously. The smaller the actuator, the more exacerbated this problem becomes due to pressure drop. Pneumatic actuators face integration challenges: each actuator requires its own pipeline, creating serial rather than parallel connections. The energy medium is related to energy rate - fewer molecules in smaller pipelines means less power. Solutions include multiplexing techniques (like Quake valves from microfluidics) and distributed computation throughout the robot.

Hydraulics and pneumatics is a polytechnic subject that studies the behavior of fluids (liquids and gases) in engineering systems, covering key concepts such as fluid classification based on viscosity (Newtonian vs non-Newtonian), density (mass per unit volume, e.g., water = 1000 kg/m³, mercury = 13500 kg/m³), specific weight, viscosity (resistance to flow), surface tension, and adhesion/cohesion forces that govern fluid behavior in mechanical systems.

This video covers the design and analysis of pneumatic actuators, explaining how to calculate force from pressure and area (F = P × A), determine acceleration using Newton's second law, and understand minimum pressure requirements for system movement. It also introduces Bernoulli's principle and the continuity equation for fluid dynamics, explaining how pressure and velocity are related in fluid systems, and discusses pressure losses in fluid conduits due to friction and turbulence.

Traditional soft actuator research focuses exclusively on structural mechanics, failing to capture the true physics of pneumatic actuation. When pressurized, fluid interactions within actuator cavities generate forces that deform the structure, yet these interactions remain poorly understood. Most published works lack detailed investigation of internal fluid dynamics, leaving critical questions unanswered about what actually happens inside pneumatic networks during operation. This knowledge gap prevents standardization of soft actuator development and leads to unpredictable test results. Addressing this requires fundamentally new simulation approaches that couple fluid dynamics with structural mechanics to reveal the complete picture of actuation physics.

A fluidic control board can be programmed using Arduino to control the flexion and extension of a soft tip actuator by managing pressure valves through specific digital pin configurations (pins 3, 9, and 5), where pins 3 and 9 are initialized as outputs and turned off while pin 5 is turned on to activate the actuator movement.