Building robots for underwater exploration and photography is a fun and challenging hobby. Whether the bot is a camera mounted on a suspended ROV or a wheeled vehicle that crawls across the stream bed or ocean floor, good waterproofing is key. While solutions are as varied as the robots, the main approaches are sealing the servo itself or sealing the entire mechanism in a watertight container.
Waterproof Coating the Servo
Servos are miniature DC motors. They are used for robotic joints because they can rotate precisely and are easy to control. However, they are not waterproof without modification.
Simple servo waterproof coatings methods include inserting it into a balloon or dipping it in a plastic coating compound. These methods can work well for short immersions in a low-pressure underwater environment. However, both leave the servo shaft vulnerable to water intrusion.
Watertight Sealing the Servo
Sealing the servo is a more reliable method of waterproofing. While cyanoacrylate glues will work, nonconductive waterproof epoxy is easier to use and gives a better result. As a final precaution, filling the inside of the servo with a non-conductive oil, such as mineral oil, will further protect the mechanism from water.
A final method is to seal the robot mechanism, batteries and circuits in a watertight case. This method is good for building an underwater vehicle. The case can be built from scratch or start with a manufactured watertight box. Sport boxes for fishing and diving come in a variety of shapes, sizes and depth ratings. Transparent boxes allow for inspection without opening the box once it is sealed.
Wheels or propellers are affixed to the box with noncorrosive brass screws, and all holes are filled and sealed with marine-grade epoxy paste. Wires that penetrate the case are sealed inside and out with silicone.
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