Pentapedal Soft Robotic Starfish

(Solo Project)

Full CAD rendering of final design (bottom perspective).

Full CAD rendering of final design (top perspective).

Fully-fabricated assembly, showing the robot's ability to stand upright and support its own weight without any buckling of the soft silicone legs.

This project was completed in the spring of 2023 for a soft robotics course at BU. The robot is called "Starfish." It is a cable-actuated, pentapedal, silicone-based soft robot, capable of locomotion and directional control. Soft robots aim to leverage the advantages of high-compliance materials, such as silicone polymers, for novel applications. Compared to traditional "rigid" robots, it is very challenging to produce the necessary force transfers required for motion through soft materials such as silicone. Controls of these materials pose similar challenges.

While many soft robots utilize pneumatics or shape memory alloys (SMA) for actuation, I've always had an interest in cable actuation and aimed to see whether this method of actuation could be leveraged.

Design

Exploded drawing view of final Starfish soft robot design. Featuring 3 MG90s metal-geared servos, with silicone (Ecoflex 00-30) limbs and PETG torso. Full components detailed in BOM.

CAD rendering Tri-hub component, which was 3D-printed in PETG for durability and ease of threading fasteners. The hubs top face has grooves which maximize adhesion of silicone to the part. The channels were designed to minimize friction, and maximize transfer of mechanical energy during tensioning.

This final design was the product of many iterative prototypes.

Fabrication

Diagram of silicone mold with key features labeled.

Completed mold with Tri-hub and servos fully seated; ready for silicone pouring.

Mold filled with curing silicone.

Live Demo Video

Demo video of final operational robot featuring initial bench tests to validate both electromechanical control and forward, left, and right maneuvering capabilities.

Controls

C++ code for real-time control of all three servo's using pair of two-axis joysticks.

Demo set up of 3D-printed joystick enclosure and prototyping board with servo wiring and DC power input.

Conclusions

Applications for soft robots include medical robotics, biomedical engineering, and other use cases where robots come into close contact with human beings or other fragile projects, e.g. produce packing, harvesting fruits and vegetables, and so on. In these settings, soft robots can leverage their compliance to reduce risk to humans and other fragile objects they interact with. These same properties make soft robots promising candidates for navigating confined spaces, where traditional rigid robots would be unable to reach (such as in remote rescue operations, or space exploration).

This robot ultimately participated in a multi-school soft robotics competition and earned the fastest run times on several of the main events, which entailed maneuvering a range of obstacles and differing substrates (e.g. traversing loosely-packed rice, turning corners, transferring objects from one location to another, and climbing inclined planes).

Diagram of silicone mold with key features labeled.

Completed mold with Tri-hub and servos fully seated; ready for silicone pouring.

Mold filled with curing silicone.

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