The vine robot, developed at Stanford University, is a soft robot that forms a growing tub-like structure through a process called eversion, i.e., turning itself inside out. In this project, a digging mechanism was attached on the tip of the vine robot that it pushes forward in order to navigate underground. Once fully grown, the robot could then be used as a pipe to facilitate subsurface drip irrigation, which, despite being over 95% water efficient, is severely underutilized due to barriers in installation costs. Our solution, through using a digging robot, eliminates the need to dig up the surface soil to install a pipe underground which eliminates the need for capital intensive equipment and pipe installation doesn’t disrupt existing crops/lawn.

The video below shows the robot in action, digging through a 3 feet tub of soil at a depth of 6 inches. Over ten trials, the robot moved an average of 91.1% of the forward distance.

Key features that I worked on in this robot included:

• The robot is made out of a thermoplastic polyester and thermoplastic polyurethane composite material (similar to those used in fire hoses), to ensure that it can withstand the air pressure needed to push the drill forward, while being flexible enough to evert (turn inside out)
• The drilling mechanism was chosen to be a rotating auger drill after tests with other options such as a jackhammer, water jet and needle scalar mechanism as it required the least force to go through the soil
• The fins provide the counter-torque necessary to prevent the twisting of the robot

This hardware proof of concept has a lot of room for improvement, including integrating previously researched steering mechanisms into our version of the vine robot and adding a water delivery mechanism. However, due to COVID-19, the hardware portion of the project had to be stopped midway.

Instead, we ran simulations using EDEM, to validate the design choices made. These included the shape of the nose cone that bridges the vine robot and drill and the counter-rotating fins. A video showing the simulation results is shown below.

Fundamentally, this thesis project worked to expand the applications of soft robotics. Through manipulation of the original vine robot design, including replacement of the vine material and the pressure container, and the attachment of a suitable drilling mechanism, the vine robot proved to be capable in an environment previously unexplored. It has potential for future development so that it can be used to incentivize the transition to subsurface drip irrigation.