Building an Autonomous Underwater Drone: Design, Challenges, and First Test
0:00:02 Introduction: The goal is to create a self-swimming submarine capable of long-distance, autonomous underwater exploration (e.g., searching for shipwrecks).
0:00:14 Challenges: Autonomy is difficult due to: 1) Prior experience was with manually operated drones, the new drone must navigate on its own. 2) Underwater GPS is unavailable. 3) Long-distance travel with high reliability is needed.
0:01:26 Series Overview: This is the first video in a three-part series, focusing on building the drone from scratch and conducting its first autonomous swim.
0:01:39 Long Distance Solution: A long, tubular design is chosen to maximize battery capacity (for 12+ hours of operation) while minimizing drag (frontal area).
0:02:58 Steering Module: A 3D-printed steering module houses fins and a single motor for propulsion, optimizing energy efficiency.
0:03:33 Propulsion: A high-quality t500 Thruster from Blue Robotics is used.
0:03:36 Fin Design: The fin design is inspired by a shark's fin for optimal maneuverability. Servos control the fins for pitch, roll, and yaw.
0:05:06 Buoyancy and Trim: Careful consideration is given to weight distribution, using buoyancy foam to counteract the weight of the motor and servos.
0:05:40 Waterproofing: Waterproof connectors, penetrators, and a polycarbonate end cap ensure the electronics remain dry.
0:06:12 Design Benefits: The design is simple, hydrodynamic, and allows for future upgrades (e.g., sonar).
0:06:40 Localization without GPS: Since GPS doesn't work underwater, a Doppler Velocity Log (DVL) would be ideal, but it's too expensive ($8,000+).
0:07:45 Buoy with GPS: A temporary solution involves a surface buoy with a GPS, tethered to the submarine, providing location data within a 3-meter accuracy.
0:08:46 Autonomous Control: The software, running on a Raspberry Pi, uses GPS data from the buoy to calculate the angle to the next waypoint and control the drone's yaw and pitch.
0:09:52 Control Software: A Pixhawk flight controller handles the low-level control of the drone's orientation, receiving high-level commands (target yaw, target pitch) from the Raspberry Pi.
0:10:20 Electronics: include a Raspberry Pi, a Pixhawk, a Wi-Fi router (for wireless mission uploads), and a battery pack.
0:11:10 First Test: The first autonomous test takes place in a river with a safety tether.
0:11:57 Initial Problems: The drone struggles to turn effectively, and the water's salinity affects buoyancy, requiring additional weight.
0:12:29 Second Test: Larger fins improve the turning radius, but the drone is slow and struggles to descend.
0:13:08 Servo Failure: A critical servo motor burns out, requiring a significant modification.
0:13:32 Quick Fix: The failed servo is replaced with a motor mounted at the front, providing a makeshift yaw control.
0:15:56 Successful Autonomous test (Modified): The drone, with new steering and fins angle adjustments, successfully completes a short autonomous mission, maintaining a near target depth (with some deviation), proving the basic functionality of the autonomous control system.
0:17:09 Next Steps: Future improvements include a more stable buoy and removing the long tether to reduce drag.