Steps to build a DIY low-cost fixed-wing drone for biodiversity conservation

well as to a reduction in time, cost and logistical challenges as compared to other means of obtaining aerial imagery, such as satellite or manned aircrafts [9, 10]. The majority of biodiver- sity studies conducted with drones use Small Unoccupied Aircraft Systems (sUAS) weighting 2–5 kg with a wingspan smaller than 3 m and payloads below 1 kg, they are generally electri- cally powered and operate at low altitudes [7, 8]. Despite the growing popularity of drones, their acquisition cost along with high mainte- nance and training costs are the main factors constraining their use in research. In the current scenario, where the greatest loss of biodiversity is concentrated in low-income tropical coun- tries [11], low-cost prototyping is a new way of helping local agents to preserve biodiversity [12]. Low-cost drone development initiatives (conservationdrones.org; diydrones.com) and open-source software (ardupilot.com; opendronemap.org) are gaining popularity in the drone and scientific community. DIY (Do It Yourself) models offer unlimited opportunities for researchers who need tailor-made solutions while optimizing cost-benefits [13]. ArduPilot, an open-source project combining software and hardware-plus-sensors for drones (copter, plane, rover and sub), is a positive example where sharing knowledge through DIY concepts can gen- erate significant technologies in the scientific environment. Along with the significant growth in the use of drones in biodiversity conservation in the past 10 years [1, 14] some studies on building DIY fixed-wings drones for conservation pur-

poses have been published [9, 15–19]. While these contain descriptions of the systems, they do not provide detailed information of the building process, which precludes their replication by other potential users. In the next sections we describe step-by-step the development of a low- cost, fixed-wing drone specifically designed for conservation purposes in large protected areas. It is inspired by the conservationdrones.org and diydrones.com websites, prioritizing simplic- ity, a positive cost-benefit balance and an open source model in the manufacturing process (Fig 1). We provide the basic construction and parameterization details in order to allow repli- cation by individuals without prior experience in electronic works. The budget is kept to a maximum of $ 1000. We describe how we tested the performance of the model, in terms of flight autonomy, coverage and data collection with high spatial resolution. In addition, we dis- cuss the potential uses of this model in applications aimed at monitoring protected areas and deforestation activities. Materials and methods Step 0: Choosing drone type The first important step to integrate drones in conservation research is deciding the drone type. The drone type has to be aligned with the flight mission profile and, in order to define the mission, the scientific objectives need to be previously defined, at least regarding operation range, terrain characteristics, mission duration and payload needs. Drones can be mainly classified into two types according to the principles of flight and

aerodynamics: fixed-wing (planes) and rotary-wing (helicopters and multicopters). Fixed- wing models depend on forward motion for lift; they need to be constantly moving forward at a certain speed that can support them in the air, so that they tend to have more efficient aero- dynamics. This allows longer flight durations, which makes them appropriate for working at large scales such as intended in this study. However, they require open terrain to take off and land, which may limit their use in dense vegetation scenarios. In the Rotary-wing models the engine propellers are responsible for both lift and thrust, hence the vertical component of the engine force is lift, and the horizontal component is the thrust [20]. They can support them- selves in the air without a need for constant movement, which allows them to take-off and land vertically from a small patch of open terrain, and to hover in stable ways above a fixed PLOS ONE Building a DIY low-cost fixed-wing drone for biodiversity conservation PLOS ONE | https://doi.org/10.1371/journal.pone.0255559 August 13, 2021 2 / 17 collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist.