Bio-inspired Pneumatic Amphibious Soft Robot: Implementation and Motion Analysis

We achieved the second place in the graduate project competition in PME department.

Abstract

Our project has successfully manufactured a functional amphibious soft robot via additive manufacturing. The robot is capable of swimming at a maximum speed of 0.40 BLS (Body Lengths per Second) and walking at a speed of 0.01 BLS. We observed that incorporating grooves and fin-like structures enhanced the robot's swimming capabilities, enabling faster and more stable movement under the same condition. Additionally, we have introduced an sawtooth limb design to facilitate ground locomotion. We anticipate that this robot could be instrumental in wilderness exploration where hard robots and humans face limitations. 

Objectives

Current exploration robots lack adaptability to different environments, while soft robots, with their excellent flexibility and deformation capabilities, can adapt to narrow spaces like caves. We take inspiration from nature, using the salamander as a reference to mimic its terrestrial crawling and swimming abilities. This project utilizes 3D printing to create a soft robot structure capable of both swimming and crawling.

Materials and Method

First, we use Inventor to design the mold and print it with a 3D printer. We specially designed this split mold to facilitate demolding later and to extend its lifespan. Next, we prepare the silicone, vacuum it to eliminate bubbles, pour it into the mold, and wait for it to solidify before demolding. Then, we assemble the different parts. For the middle of the body, we use a composite material of silicone and fabric for the fixed end, waterproof tape for the tail, and harder Teflon tubes for the pipes connecting to the body.

The following image shows the system providing power, including the pump, valves, and controller. 

During the actual test, we will record videos for later motion analysis. We use the Tracker video analysis software to calculate swimming speed, oscillation frequency, and oscillation angle. Additionally, we use a syringe and a pressure gauge to measure the relationship between the oscillation angle and pressure. 

Result

According to the experimental results, in the graph showing the relationship between oscillation frequency and swimming speed, the following observations can be made:

The red section represents the data distribution for the tail without grooves, corresponding to lower swimming speeds, indicating less forward movement. The blue section represents the data distribution for the tail with grooves, which shows not only faster swimming speeds but also an increasing trend with higher frequencies. For example, with a half-body grooved structure, a frequency of 2.31 Hz can achieve a swimming speed of 0.40 body lengths per second.

Looking at the graph of the relationship between pressure and angle, we can observe that the oscillation angle is greater with the grooved design at the same pressure. This indicates that to achieve the same amplitude, the structure with an inflatable half-body and grooves requires the least air pressure, making it a more efficient motion design.

From the above results, we found that swimming is mainly influenced by the tail. The grooved structure allows the tail to generate a larger oscillation angle at the same air pressure, and limiting the chamber's expansion to the posterior section makes the motion more efficient, increasing movement speed. Therefore, the design with an inflatable half-body and grooves has the fastest swimming speed.

Currently, for crawling, we have designed a serrated structure on the soles to modify the distribution of ground friction. Additionally, we use a composite material of silicone and cardboard at the fixed end to increase mechanical strength and support the body during crawling. In the future, we aim to optimize the legs and install a sensor system for exploratory applications.

The poster pdf document is attached below. Feel free to check it out!