Oogway

Our control system ensures precise and stable robot movement through a blend of feedforward and feedback control mechanisms. Feedforward control maximizes stability by counteracting persistent forces like buoyancy, while feedback control, implemented via Proportional-Integral-Derivative (PID) loops, ensures smooth navigation towards the target. 

Further enhancing performance, the thrust allocator solves a quadratic programming problem using advanced numerical optimization techniques to determine the necessary force for each thruster, enabling the robot to follow the desired trajectory while minimizing energy usage. These forces are then transformed into pulse widths via a nonlinear mapping and pulse width modulation is employed to spin the thrusters. This sophisticated approach guarantees precise maneuverability across diverse environments and conditions.

Built on top of Foxglove Studio using the React Material UI library, the Duke Robotics GUI features a modular and modern design and allows us to easily monitor and control our AUV during pool tests. We can receive real-time updates on the status of our onboard computer, sensors, thrusters, and battery. We can observe the performance of the czontrols system and tune PID constants on-the-fly. We can use a joystick to control the robot directly. Individual panels are organized into layouts and easily deployed using a custom CLI. The GUI also supports replaying recorded ROS bag files for offline debugging and analysis.

Detection

The computer vision (CV) system uses stereo and monovision inputs from both our DepthAI and USB cameras to locate items underwater to complete our underwater tasks. For simpler prediction tasks, we employ HSV filtering and contour matching to identify the buoy, path markers, and bin. For more intricate images encountered in the gate, torpedo, and octagon tasks, we utilize YOLO object detection models. Our enhanced CV pipeline seamlessly integrates these methodologies, dynamically adjusting to optimize detection speed and accuracy for various tasks.

The electrical stack is the heart of the robot. Its primary responsibility is twofold — power all components, and ensure all data gets to the right places. This includes everything from communicating with all sensors, powering the robot computer, and even ensuring a network connection to the GUIs running on our landside computers.

This year, we rebuilt our electrical stack for two reasons. For one, we recognized a need for future expansion and overall optimization of component layout. And second, our capsule flooded.

Oogway relies on many sensors to track both external and internal conditions.

Our primary sensors determine the robot’s state, that being it’s 6 degrees of freedom: x, y, z, roll, pitch, yaw. Our IMU, DVL, and pressure sensor are fused in software to provide an accurate state. The IMU and DVL both have their own direct UART serial connection to the PC whereas the pressure sensor is read through an Arduino and sent to the main ROS node over USB.

Oogway has two sonars onboard, both of which are connected to the computer’s USB.

We also have an internal voltage sensor to monitor the batter and adjust thruster efforts, a temperature sensor to monitor capsule heat, and a humidity sensor to detect water ingress. Each of these three internal sensors are read with an Arduino as well.

Oogway has four cameras that we use for CV and monitoring. Two cameras are simple USB cameras rated for underwater and two are sophisticate stereoscopic cameras with internal processing. These cameras represent a significant demand for both our power and data systems.

We also utilize downward facing cameras to track path markers on the pool floor.

Oogway has 8 thrusters and it is electrical’s reponsibility for providing the layer of hardware abstraction used by controls. There are multiple challenges associated with the thrusters.

For one, the thrusters are located outside the capsule. With three 14AWG wires each, the thrusters introduce significant capsule penetration. Additionally, the ESCs mounted inside the capsule are physically large and come with significant wire mass when all power, data, and output wires are connected.

Additionally, the thrusters each require a precise PWM signal to be generated from our PC. Therefore, we run serial communication to an Arduino Nano Every that use an I2C multiplexer to initialize and control all thrusters. We have made corrective offsets to hardware defects that we measured on some ESCs.

Our marker dropper contains a servo that is connected to one of our Arduinos. Upon receiving the proper command over USB from ROS, we can individually drop both rounds from our dropper.

Ensuring the watertightness of the electrical stack is one of the mechanical team’s top priorities. The stack is enclosed by an off-the-shelf Polycase capsule and a custom-machined aluminum plate with space for WetLink penetrators and SubConn connectors. The bottom plate is also anodized to ward off corrosion in saltwater environments. 

This year, we added a new custom-made titanium top plate in response to a number of small leaks during last year’s competition. The four brass inserts molded into the Polycase capsule began to fail due to wear and tear over a year of use. The new titanium plate bypasses this weak point and applies even pressure across the entire capsule, improving performance and decreasing deterioration.

The primary goals for all component mounts on Oogway are flexibility and rapid prototyping. Oogway’s aluminum rails allow us to move components around easily to optimize for factors such as buoyancy and placement of sensors. This year, this came in handy for the hydrophone mounts, which underwent several different designs and locations as the acoustics subteam developed their code. 

We primarily use 3D-printed mounts to keep Oogway lightweight and allow for updated designs to be fabricated consistently and quickly. The battery mount, for example, broke frequently during last year’s competition. This year, we were able to quickly prototype and test new designs and print backups just in case. We also designed several new parts this year, such as a marker dropper, two new sonar mounts, three new camera mounts, and a new adjustable buoyancy system.

We added actuators to Oogway for the first time this year. The marker dropper mechanism uses Blue Trail Engineering’s waterproof servo to hold up to two markers in place, and a rotation to either side allows these markers to be released. This gives us the flexibility to choose when the markers should be dropped and how many should be dropped at a time. 

While not yet on Oogway, we are also prototyping a torpedo launcher using the same waterproof servo, which will be responsible for releasing the torpedoes. Like with the marker dropper, we aim to use one servo to control both triggers independently to give us the most flexibility during a run.