Multi-Environmental Drone Avionics: Circuit-Level Waterproofing for Aerial and Aquatic Operations

– The development of multi-environment drones capable of transitioning between aerial and aquatic domains presents a critical engineering challenge: protecting sensitive avionics from fluid ingress without degrading flight performance. Traditional underwater robotics rely on heavy, sealed enclosures that drastically increase vehicle mass and generate excessive positive buoyancy, rendering atmospheric flight impractical. This paper presents and validates a lightweight, circuit-level waterproofing methodology designed specifically for amphibious unmanned aerial vehicles. A compact 145 mm wheelbase quadcopter was constructed using a carbon fiber frame integrated with a central processing architecture and an ExpressLRS 900 MHz communication system. Aerol silicone-elastomer conformal coating was systematically applied across all exposed printed circuit boards through a controlled three-stage spray process involving isopropyl alcohol cleaning, polyimide tape masking of sensitive sensor ports, and staged curing intervals. Empirical submersion testing confirmed that the drone sustained continuous powered operation underwater for 30 minutes with zero electrical faults. The hydrophobic treatment added only 12.4 grams to the total system mass, preserving the aerodynamic thrust-to-weight ratio. These results demonstrate that conformal coating provides a viable, mass-efficient alternative to bulky enclosures for amphibious drone development.