Design, fabrication, and locomotion analysis of an untethered, miniature, legged, compressible, soft robot: CSQUAD

Abstract

Conventional robotics has been effective for industrial applications such as fast, precise and accurate production or for sophisticatedly controlled systems for the last couple of centuries. However, as the robots become more ubiquitous in every-day lives of people, the drawbacks of conventional and rigid robots have become more and more apparent. One of the biggest problems that soft robots solve is the safe interactions with humans. Whether it be a minimally invasive surgery or a search and rescue operation under rubble, the soft robots offer better performance especially in terms of compliance compared to their rigid counterparts. With especially the search and rescue environments in mind, this study presents an untethered, miniature, legged and compressible soft quadruped (cSQuad). This robot is equipped with C-shaped legs for better locomotion per-formance on unstructured surfaces. It is made out of soft materials, mainly from polydimethylsiloxane (PDMS), it utilizes a flexible printed circuit board (PCB) and only some small sensors, actuators and electronic components are made out of rigid materials. The main goal of this robot is to have the ability to pass through openings that are smaller than its cross-section. In order to achieve this goal, the robot is designed to be compressible. Both the body of the robot and its C-shaped legs can compress themselves using shape memory alloy (SMA) springs. The design and fabrication steps of cSQuad is explained in detail and the tests have been done to verify that the robot can reduce its cross-section area by at least 25%. cSQuad is the successor of SQuad which is also a soft quadruped with C-shaped legs. Before starting the design of cSQuad, the locomotion performance of SQuad was studied to make sure that it would be worth continuing to design new generation of soft quadrupeds. This study was a comparative study between the soft quadruped (SQuad) and its rigid and hybrid twins. The study consisted of speed, pitch and roll angle, body centroid position and obstacle climbing per-formance analysis. The results of this analyses showed that even though the soft robot was slower it gave better performance in terms of obstacle climbing and smooth locomotion. This gave us the confidence to continue improving the robot which resulted in designing of cSQuad. SMA springs of cSQuad are placed on specifically calculated locations on the body and the legs of the robot to achieve optimum compression performance. To transmit power to the SMAs on continuously rotating legs, a custom slip-ring device was built utilizing pogo pins. The compression tests for the legs and the body were conducted separately. Then, a robot with both leg and body compression was built and tested. As a result, a robot with the capability of reducing its cross-section area by at least 25% is built and tested. This robot can be used as a base design for the new generation of robots that could be used in search and rescue operations. It has the potential to be equipped with specific sensors for specific tasks. The fabrication and design steps can also be considered as a framework for fabricating soft robots in general.