In this project, we were tasked with creating a 2.5 axis machine of our choosing. We decided to make a machine to individually probe plant from below and read out the moisture content of their soil. The intention of this prototype is to act as a proof of concept for a larger scale operation. In, say, a greenhouse with 50-100 plants, it is daunting to place a moisture sensor in each plant. The sensors have a limited life span and would need to be changed regularly. With our design, only one sensor would need to be replaced. Our design is specifically meant to be as low profile as possible vertically, so as not to make the device as a whole too tall or unstable. We used three stepper motors connected to pulleys to move the sensor precisely below each plant and a servo motor to actuate a rack and pinion setup. This rack and pinion moves the sensor up into the bottom of the plant, where it can take a moisture reading and record it. The data for the sensor and motors is relayed to an Arduino uno with a CNC shield attached. The planter itself is made of 1/8 inch MDF, which has been laser cut to size, with holes for bolting other components to it and for bolting the planter to the device’s frame. The plants themselves are pressure fit into holes in the planter. Making an exact CAD model of the entire machine was extremely helpful for achieving accurate placement of the plants and ensuring there was enough space for the end effector.
