Most commercially available 1:18 scale RC boats are designed solely for surface operation, lacking the structural integrity, waterproofing, and buoyancy control needed for submersion. While RC submarines are available as niche hobbyist products, they tend to be expensive, specialized, and limited in depth capability. This project aims to bridge that gap by converting an off-the-shelf RC boat into a functional submarine, applying engineering principles to address challenges in waterproofing, ballast design, and underwater propulsion.
The project developed a small RC submarine using a combination of custom-designed components and repurposed RC boat hardware. Rather than modifying the original RC boat hull, a fully enclosed hull was designed and manufactured using 3D printing. Due to sizing of components, the off-the-shelf boat hull would not have been large enough to encase all required systems. This approach also allowed the hull geometry to be optimized for waterproofing, internal component integration, and structural integrity during submersion. Additional 3D printed control surfaces, including the rudder, were designed to provide steering and stability underwater.
Buoyancy control was achieved using a Reverse Recirculating Compressed Air Ballast System (RCABS-R). This system regulated buoyancy by transferring air between compressed air tanks inside the sealed hull and a flexible ballast bladder located in the free-flood section of the submarine. Inflating the bladder displaced water and increased buoyancy, while withdrawing air allowed water to re-enter the space and reduced buoyancy, enabling the submarine to submerge.
To minimize cost and system complexity, propulsion and control components from the original RC boat, including the motor, propeller, and steering servo, were reused in the submarine design. A wired surface buoy was also implemented to enable communication with the operator and ensure reliable signal transmission during underwater operation.
Over two quarters, our team designed, manufactured, and integrated a functional RC submarine prototype. Key deliverables included fully 3D-printed dry and free-flood hulls, an integrated control system, and propulsion and ballast subsystems. Testing confirmed reliable actuation of electronics, thrust generation, and successful air transfer within the ballast system, demonstrating feasibility of the buoyancy control approach.
The prototype did not fully meet performance requirements. Buoyancy was overestimated due to free-flood hull manufacturing, preventing submersion even with the ballast deflated. Steering performance was limited by weight distribution and control surface effectiveness. The primary failure was air leakage in the ballast system, causing pressure loss and loss of buoyancy control.
These issues are addressable with further development. Reducing free-flood hull displacement, improving control surface geometry, and implementing more robust sealing and fittings in the ballast system would enable reliable submersion and maneuverability.