Automated Mast Sorting Device

Figure 1: Final design for mast sorting device. Background

At the base of every forest ecosystem are mast, or the fruits of trees and shrubs, which includes acorns, hickory nuts, and beech nuts. Mast play several fundamental roles in ecology, from sustaining animal populations to influencing reproduction patterns. Variations in masting cycles can cause fluctuations in animal populations and can provide important information relating to weather patterns and other environmental factors such as climate change. One of the main goals of the Duke Forest is to study masting cycles in order to better understand forest trends and to educate the public about the environment. To conduct this research, the Duke Forest staff collects thousands of mast to study. The original method of mast collection employed by Duke Forest researchers was a simple laundry basket with a net on top to separate out sticks and leaves. However, it takes Duke Forest researchers a significant amount of time to sort the collected mast by genus and to remove all other organic debris by hand for testing after collection. Thus, the Duke Forest researchers sought a design which would ultimately remove organic debris from the collected mast as well as sort the mast by genus. In the Fall of 2018, this design project was assigned to a group of first-year Duke engineering students in partnership with Duke University’s First Year Design experience to give practical, real-world applicable tasks to incoming freshman engineers. The project was then continued in the Spring of 2019 by a smaller team. The final design for the mast collector is shown in Figure 1.

Figure 2: Final prototype of mast collector. Key Design Features

Before mast can be sorted by genus, they first need to be isolated from other natural debris. In pursuit of this goal, the device was designed with a clear focus on the efficacy of the collector: accurately filtering sticks, leaves, and other debris while still collecting all of the mast. Other factors were also considered, such as the cost, weight, and durability of the collector. The final mast collector design is split into two parts: an upper collector and a lower collector. The as-built prototype is shown in Figure 2.

Upper Collector

To prevent larger branches from falling into the device and clogging up the lower collector, the upper filter was created using a PVC frame and a flexible mesh net. The goal of the upper filter is to block out larger debris that could possibly impede the collector’s function by blocking the metal ramp while still allowing mast to pass through, allowing for the collector to operate for a longer time before requiring maintenance. A closer look at the upper collector is presented in Figure 3.

Lower Collector

The lower collector, shown in Figure 4, is made out of a strong and lightweight polycarbonate material and held together by lightweight 3D printed plastic joints and metal L-brackets, which allows for ease of transportation and maneuverability, along with making the entire design modular. The two ramps are made from aluminum sheet metal. This component of the device separates mast from other tree debris using their kinetic energies. Since mast are more spherical in shape, they are able to roll down the ramp while other debris slides at a much slower speed. This difference in speed allows the mast to launch over the gap between the ramp and the collection bin while sticks and leaves fail to clear the gap. The unwanted debris then slides into the gap and out of the bottom of the mast collector onto the forest floor.