Every kindergartener knows that water and electronics don’t mix, which is why you might be surprised to learn that you can run standard drone-style brushless DC motors underwater without any issues. While corrosion could eventually become an issue if the motors don’t have any protection, the lack of brushes on the motors means that nothing with electrical current makes direct contact with the water. That dramatically simplifies the construction of underwater ROV (Remotely Operated Vehicle) submarines. To put that concept to the test, YouTuber RCLifeOn built an ROV submarine using standard drone components.
A typical quadrotor drone, like the kind RCLifeOn scavenged for this project, contains four important electronic components: a battery pack, a flight controller (often with a built-in radio transceiver), ESCs (electronic speed controllers), and brushless DC motors. Those are exactly the components that went into this underwater robot, along with an FPV (First-Person View) camera system. To simplify the design and eliminate the need for extra motors, RCLifeOn chose a unique propulsion arrangement.
Two propellers face forward and provide forward/reverse thrust and yaw control. The other two propellers face upwards, providing up/down thrust and roll control. There is no direct control for pitch alone, but RCLifeOn can sort of maneuver pitch with a combination of forward thrust and up/down thrust. That, in combination with the shape of the sub’s hull, can effectively control pitch as the craft moves through the water.
RCLifeOn designed the ROV’s hull in Autodesk Fusion 360 and then 3D-printed it. He also 3D-printed a floating radio tether, which is necessary because radio waves at this frequency have poor penetration through water. The floating tether provides a clean radio signal between the receiver and the remote, and then sends the control commands to the sub through an insulated wire. RCLifeOn strapped a GoPro onto the sub’s hull to capture presentation-worthy video and also incorporated an FPV camera for controlling the ROV in real time.
As you can see in the video, the submarine worked quite well — at least at first. But eventually water made its way through the seal in the hull and reached the flight controller and ESC electronics. Unlike the brushless DC motors, those are very sensitive to water exposure and they failed soon afterwards. But even with that mishap, this ROV proves that your conventional drone parts are well-suited to building underwater robots.