8. Soft Robotics

Introduction and Research

For the Soft Robotics week of Fabricademy, I focused on designing and creating a functional silicone bellow. My primary objective was to delve deeply into the process of designing molds, casting silicone components, and assembling functional soft robotic actuators. This exploration aimed to develop my technical and creative skills in soft robotics while addressing challenges associated with prototyping. I began by extensively researching existing soft robotics projects to understand the fundamental principles, mechanisms, and potential applications of soft actuators. This research highlighted the versatility and importance of soft robotics in various fields, ranging from medical devices to animatronics and biomimetic designs.

Inspiration

One of the primary sources of inspiration for this project was the Soft Mod Bots initiative, particularly their ingenious use of bellows in their frog and bird models. These projects vividly demonstrated the flexibility, adaptability, and functionality of soft bellows in creating lifelike movements. The ability of these designs to mimic natural forms and actions resonated with my project goals. This motivated me to design a bellow system that could be integrated into similar applications, potentially expanding their use cases in soft robotics and beyond. By studying their methodologies and material choices, I gained insights into effective design and production techniques, which significantly informed my approach.

Soft Mod Bots Website

The Bellow Project

I initiated the project by parametrically designing the bellow in Fusion 360, leveraging its advanced modeling capabilities to create a highly adjustable and precise design. The bellow's geometry featured different ridges and cavities, which were essential for ensuring smooth inflation and contraction. The parametric approach enabled quick adjustments to dimensions and structural features, optimizing the bellow’s performance. After finalizing the design, I shifted focus to creating a two-part mold to cast the silicone. This mold was specifically designed to produce only half of the bellow, simplifying the fabrication process while maintaining high accuracy. The plan was to later glue two identical halves together using Ecoflex silicone from Smooth-On, ensuring a seamless and robust assembly.

a. Design in Fusion 360

1. Defining Parameters: I started by setting up key parameters such as the number of ridges, ridge width, overall length, and inner/outer diameters. This ensured a scalable and modifiable design.

1. Creating the Bellow Section: I sketched a single ridge profile, extruded it to create a small section of the bellow, and then copied and repeated the section multiple times.

2. Joining the Sections: The repeated ridges were joined together into a single body, ensuring continuity in the design.

3. Shell Tool: The shell tool was applied to hollow out the bellow and make it flexible for inflation and contraction.

1. Splitting the Body: Using the split body tool, I divided the bellow into two symmetrical halves, allowing for mold design based on a single half.

2. Creating the Mold: I placed a rectangular block around the half bellow and used the cut tool to create the mold cavity. The mold was then refined by:

   • Adding alignment features.
   • Designing pour holes on the sides for silicone injection.

b. Printing the Mold

Once the mold design was finalized, it was exported to Cura for slicing.

Slicing Settings

• Layer Height: 0.2 mm

• Wall Thickness: 1.2 mm (to ensure strong mold walls)

• Infill: 20%

• Print Speed: 50 mm/s

• Supports: Enabled for overhanging features

• Adhesion: Brim to prevent warping

After printing, the molds were cleaned, and minor defects were removed before proceeding with the casting.

c. Casting Tests

The casting process began with preparing the Smooth-On Ecoflex 30 silicone., ensuring accurate measurements for optimal curing and performance. The first casting attempts yielded imperfect results, with minor air bubbles and uneven edges. Despite these imperfections, I chose to retain these initial casts for further experimentation, recognizing their potential value for iterative learning. These early tests provided valuable insights into the curing process, mold behavior, and silicone properties, enabling refinements in subsequent attempts.

Casting Process:

1. Mixing Ratio: 1:1 (Part A to Part B by weight)

2. Weighing and Mixing: Using a precision scale, I weighed equal amounts of both parts and mixed them thoroughly.

1. Degassing: The mixture was placed in a vacuum chamber to remove air bubbles.

1. Pouring: The degassed silicone was poured into the mold. I tried injecting it with a syringe from the holes on the side, but that did not work, so i just poured it into the open mold and closed it, with the excess pouring out.

1. Curing Time: 4 hours at room temperature.

d. Utilizing Imperfect Casts

Several initial casts had defects such as incomplete edges or tearing when removed from the mold. Instead of discarding them, I decided to seal the half-bellows by designing an acrylic mold to close the open face of the half-bellows, giving them a new functional dimension. Using waste acrylic sheets from previous projects, I laser-cut the precise outline of the bellow and assembled the pieces into a compact mold. This mold allowed me to cast silicone into the closed shape, effectively sealing the open face of the half-bellows. This adaptation not only salvaged the earlier casts but also expanded the project’s creative scope.

1. Designing a Mold: I designed a rectangular sealing mold with adjustable wall heights.

1. Laser Cutting Preparation: The design was prepared in Rhino by setting lines to hairline thickness and red color.

2. Cutting Settings for 3mm Acrylic:

   • Power: 100%
   • Speed: 20 mm/s
   • Frequency: 5000 Hz

1. Assembling the Molds:

   • The acrylic pieces were glued together using chloroform.

 - Different mold heights were created by stacking layers.

1. Using the Molds:

e. Gluing the Full Bellow

After successfully casting two perfect half-bellows, I moved on to the assembly phase. Using Ecoflex silicone as an adhesive, I carefully aligned and glued the halves together, ensuring a strong and airtight bond. This step required precision and patience to avoid misalignment or gaps that could compromise the bellow’s functionality. The curing process was monitored closely to achieve a seamless connection, resulting in a fully functional bellow ready for testing.

1. Mixing Ecoflex 30 in small quantities.

2. Applying a thin layer to the edges of both halves.

3. Aligning and pressing them together for a seamless bond.

4. Allowing full curing before testing.

f. Designing and 3D Printing Adapters

To enable inflation, I designed and 3D-printed adapters tailored to fit the bellow’s openings. These adapters, printed in PLA, were designed to snugly accommodate a range of pipe and hose sizes. By keeping the bellow openings larger, I introduced flexibility in selecting the appropriate tubing for various applications. The adapters were securely attached to the bellows, providing a reliable interface for air input while maintaining structural integrity. This modular approach enhanced the versatility and practicality of the final design.

I designed three PLA adapters:

1. For inflating the full bellow

2. For inflating the half-bellow

3. For connecting two half-bellows with a syringe in between (gripper setup)

Design Process in Fusion 360:

• Sketching the base profile.

• Extruding to create the adapter body.

• Adding fillets for smooth connections.

• Creating precise holes for airtight fittings.

• Slicing and printing with:

  • Layer Height: 0.15 mm
  • Infill: 30%

g. Paper Bird Project

I replicated the Soft Mod Bots bird by designing a paper-based model in Rhino and integrating the bellow.

Design and Laser Cutting

1. Sketching bird components in Rhino.

1. Laser cutting paper using:
   • Power: 40%
   • Speed: 150 mm/s

1. Assembling the pieces using glue.

1. Integrating the full bellow inside.

1. Observing wing movement during inflation.

h. Testing and Results

The testing phase involved evaluating both the complete and modified half-bellows for their functionality and performance. The tests included inflating the bellows to observe their expansion and contraction, assessing their durability, and exploring potential use cases. The closed-face half-bellows demonstrated unique properties that could be harnessed for specific applications, while the full bellow exhibited consistent and reliable performance. These tests provided valuable feedback for future iterations and potential improvements.

1. Half-Bellow Gripper: Successfully grasped objects using syringe-based actuation.

1. Bird Project: Worked as expected, with wings moving as the bellow inflated.

Final Thoughts and Conclusion

This project allowed me to explore mold design, silicone casting, and soft robotic movement, offering insights into adapting to imperfections and leveraging alternative solutions. The functional gripper and bird prototype highlight the potential of soft actuators in real-world applications. Moving forward, I plan to refine the molding process, explore more advanced bellows, and integrate electronics for closed-loop control in soft robotics applications.

The iterative process, from design failures to functional results, reinforced the value of experimentation and problem-solving in fabrication.

Through this journey, I developed a comprehensive understanding of soft actuator design and production, gaining hands-on experience with materials, tools, and techniques. This project has not only expanded my technical capabilities but also fueled my enthusiasm for exploring more complex and innovative soft robotics applications in the future.

Files:

• Half Bellow Mold A STL
• Half Bellow Mold B STL
• Half Bellow Face Mold DXF
• Half Bellow Adapter STL
• Full Bellow Adapter STL
• Gripper Adapter STL
• Bird DXF