Intro to Soft Robotics Workshop
How To Make (Almost) Anything, Fall 2019

Ali Shtarbanov

MIT Media Lab

alims at mit.edu

Systems built from highly-compliant materials with mechanical properties similar to those found in living tissues. Many kinds of soft robots exist, but in this workshop we will focus primarily on pneumatically actuated soft robots.

Pressure Actuated

Radial Expansion: Modular CubesBubble, Self SleeveSPA Skin

Axial Expansion: Fiber-Reinforced Actuator, Extending McKibben Muscle,

Axial Contraction: Contracting McKibben Muscle,

Twisting: Fiber-Reinforced Actuator

Bending: PneuNetsFiber-Reinforced Actuator

Gripping: SoftRoboticsOther

Growing: Vine Robots,

 

Locomotion: Rolling, Walking, Crawli, FRCMR, Millipede, Tube Climbing (paper)

Complex Movement: Honeycomb PneuNet, Stewart Platform

Semi-Soft Robots

Arthrobots: paper, video, supplementary material,

Vacuum Actuated

Buckling: Rotation, Gripping, Linear Motion

Complex Movement and Locomotion: V-SPA

Surface Display: Soft Reconfigurable Surface

Particle Jamming:

FlexShapeGripper, DIY Gripper, Jamming User Interfaces

Layer Jamming:

JamSheets (paper)

Laminar Jamming, (paper1, paper2) :

Hybrid Gripper

Materials

Equipment

Vacuum Pump (with pressure relief valve)

Vacuum Chamber

Mixing Container

Stirring Rod

Spreader

Transparent Cover

Glass

Acrylic

Weights

Lab Coat

Squeeze Bottle with Cap

Heated Plate (60-80 degrees C)

Curing Oven

Electronic Scale (with no Auto-Shutoff)

Actuator Design Tips

Create a positive CAD model of the actuator with at least a Base and a Top part, and assembled them to confirm proper fit.

Design the base part with an outer perimeter slightly larger than that of the top part.

Carefully plan where the air will be coming from and how it will flow between chambers.

In SolidWorks use Section-Cut feature to inspect the internal structure of the chambers.

Include a hole (with an elevated tail) for the supply tube into your CAD design. 

Don't just punch a hole for the tube at the very end, as most online tutorials would have you do.

The hole diameter should equal that of the tube, or be slightly larger

Make the actuator wall thicknesses parametrically represented

T >= 1.75mm

Wall should be thick enough so that the structure won't buckle under its own weight.

Create the molds from your positive CAD models.

In SolidWorks you can do this using either Combine, Intersect, or Cavity feature.

Fillet all interior edges and corners of the molds to prevent tearing of the silicone during demolding.

R >= 0.25mm

(You can add the fillet to the exterior edges of the positive model or interior edges of the negative model.)

Make your walls slightly drafted whenever possible (rather than vertical) to make remolding easier.

Sometimes this is required, especially if your mold is taller than a couple centimeters.

Print your mold with 100% infill.

Actuator Fabrication Tips

Material Preparation:

1. Before you start, determine what is the total mass of silicone you would need, then mix about 10-15% more than the minimum required amount. An easy way to do this is by filling the molds with water and measuring the water volume

(The specific gravity of silicone is 1.07, thus for every 100g of water, you need 107g of Silicone to fill the same volume.)

2. Add 2-3% Slo-Jo to Part B and mix thoroughly. Note that this typically means just a few drops of Slo-Jo!

3. Add an equal amount of Part A and mix thoroughly

4. Put mixture into the vacuum chamber and degas until all bubbles are gone.

Bubbles are the main enemy, leading to weakness, tears, and leaks.

Ensure that your mold is 3D printed with 100% infill to minimize the air trapped in the material during the printing process.

Air trapped in the 3D printed material will expand and escape through the walls when the mold is under vacuum. This could lead to formation of new air-bubbles in the silicone during degassing. 100% infill helps prevent this problem.

But even with 100% infill, some air would still be trapped in the structure. Thus, another precautionary measure you can do is to print your structure such that the air is more likely to escape through the tap rather than through the sides when placed under vacuum. This can be achieved by adjusting the advanced settings in your 3D printer's slicer software and making the top more porous than the walls.

Use a vacuum chamber for degassing after each of the following steps:

After mixing parts A and B.

After pouring just enough silicone to cover the mold surface.

After filling the mold.

Variable vacuum leads to faster bubble extraction than constant vacuum.

Use the pressure relief valve to oscillate between max vacuum to low vacuum several times.

Bubbles are much more likely to form at corners and edges than elsewhere in the mold

Fillet all interior corners and edges of your mold

Always use Slo-Jo, even if you don't need the extra working time it provides.

Lowers the viscosity of the silicone

Reduced bubble formation.

Bubbles can escape more easily.

Allows more time for trapped bubbles to escape.

Surface tension causes uneven surfaces and leads to poor actuator behavior. 

Overfill the mold and put a transparent acrylic cover (and weight on top) to achieve smooth, even surface.

Overfilling helps ensure you don't trap any bubbles while putting the cover. 

Lower-durometer actuators can operate at much lower pressures, but also apply lower forces. 

Jamming chambers are great in this case for add stiffness to the actuators.

Use Sil-Poxy to seal the supply tube to the actuator.

Only use silicone tube and never a vinyl tube, or it will start leaking eventually.

Ecoflex / DragonSkin do not provide as strong seals as Sil-Poxy.

TechBond (tbbonding.com) also works as an  adhesive for silicone materials.

However, the bond is quite rigid, and the product is quite toxic while working with it.

FlowIO Platform

Fully Integrated Wearable System

Pumps

Valves

Sensors

Microcontroller

Power Electronics

Built-In Battery

Rechargable via Micro USB port

Control Options

Firmware Programming

Web-GUI via Google Chrome

Processing GUI over USB

Processing GUI over BLE

Port Independent Pneumatic Capabilities

Inflation

Release

Vacuum

Pressure Sensing

Pressure Hold with zero power

Dynamic Flow Control

Reconfigurable Pneumatic Configurations

General Purpose

Parallel Inflation

Series Inflation

Parallel Vacuum

Series Vacuum

Communication Ports

Bluetooth Low Energy

Standard Bluetooth

Micro USB

14-Pin Expansion Port

I2C

SPI

UART

GPIO Pins

Peripheral Modules

Expansion Port Breakout

Sensors++

16 Channel Analog Input

Documentation

Libraries & APIs

Source Code

Examples

Research paper

Video

Make your own

Application Spaces

Soft Robotics

Telepresence

Haptic Feedback

User Interfaces

Wearables

Assistive technology

Swarms

Assignment

Make something soft that can do an action under change of internal pressure. 

Try incorporating into your project a combination of the concepts you learned today (e.g. Hybrid gripper).

You can work individually or in groups, depending on the complexity of your projects.

(You will have access to a FlowIO Platform device if you need one.)