We have developed two prototypes of the soft snake robot. The first one does not include the inextensible material embedded between the pneumatic chambers. This prototype relies on the uninflated half of the actuator to act as the strain-limiting layer required to execute bending. The development of this snake, as well as the development of our “circular gait” which approximates lateral undulation, can be seen in our paper. This prototype was developed first as the fabrication of soft robots is a giant open problem in the field.
Current methods are done by hand leading to inconsistencies, and behavioral quirks for each robot. Embedding a layer of inextensible material is an additional complexity that leads to more opportunities for inconsistencies to occur. The performance of the robot in millet was fine, traveling around 0.01 body-lengths per second on average. However, the robot was not successful on any other terrains, and from observation, limiting extension seemed like the next step to take in improving the robot. Therefore we developed an inextensible prototype which has been tested in a wide variety of environments.
The fabrication process for the inextensible robot was complex, and had many steps where inconsistencies could arise. Further research is being conducted into better fabrication methods, both with molding and 3D printing out of our lab. There are many problems with this method including the choice of inextensible material, but this method has produced the most consistent actuators out of all the molding methods we have tried. Our molds are 3D printed using PLA, and provided here. We use EcoFlex 00-30 to make our actuators, which takes about 3 hours to air cure. We have tested many materials for the inextensible material, including cotton, polyester, and woven fiberglass. Each have their advantages and disadvantages both in performance and in the fabrication process. We have used the woven fiberglass (window screen material) as it is easier for the fabrication process, but it does introduce some inconsistencies when stretched as the woven structure can cause diagonal elongation resulting in the twisting of the actuator at high pressures.