An underwater robot is mostly a waterproofing project.
An underwater robot is mostly a waterproofing project. Controls are not hard compared with keeping electronics dry, managing buoyancy and recovering the robot if something fails. Start tethered so power, video and retrieval stay simple.
Build and test in stages: empty enclosure in a bucket, then shallow pool, then short missions.
Build and test in stages: empty enclosure in a bucket, then shallow pool, then short missions. Add leak detection inside the electronics tube and keep the first version slow, visible and easy to pull back by the tether.