MECHANICAL TEAM
Mechanical members focus on designing, building, and testing the main hull, chassis, and external systems needed to run our robots. The vast majority of design work the team does is in SolidWorks and members utilize various machine shops on campus to realize projects. New members are accepted regardless of experience or academic year and are aided with lessons and one-on-one pairing. The team’s goal is to ensure that all members have the opportunity for hands-on experiences and learning that is often lacking in the traditional classroom.
About the Subteam
The majority of our design work is done in SolidWorks, the same CAD software that is taught in ME courses. In addition to design, we also use SolidWorks to run stress/strain and other simulations of our designs. We apply the fundamental principles of Mechanical & Aerospace Engineering, Materials Science, and ergonomic design to create the systems our robots need to run.
Members machine much of the parts needed for our designs. Whether drilling and tapping holes into a small plastic part or shaping a block of aluminum, members can get experience on the Bridgeport, lathe, CNC, waterjet and more! Additionally we often modify/create systems by hand, as seen in a picture at the bottom of the page, wrapping the coils for our Gauss-Gun Torpedo Launcher.
Everyone is welcome, regardless of skill level. Being part of the mechanical team will give you real design, manufacturing, and system analysis experience. Whether you are interested in design, mechanics, failure analysis, or robotics – you’ll find a fit with UWRT.
Talos
The largest project for the Mechanical Team this year was developing the new vehicle, Talos. The four main projects on Talos included the chassis redesign, new smart batteries, improving the task mechanisms, and creating electronics cages for the Mark 2 Electronics. Using Tempest’s hull as the base, these projects all contributed to forming this year’s new vehicle, Talos.
This year, we continued to use Talos, our well-established AUV, while integrating several new enhancements to address previous shortcomings and improve overall performance. The decision to retain Talos was based on its proven capabilities and our strategic focus on refining existing systems for optimal performance in the upcoming Robosub 2024 competition.
Background and Rationale: Tempest, our AUV from two years ago, presented several issues that led to the development of Talos. The HDPE structure lacked rigidity, and the bonded joints on the undercarriage were prone to failure. Its large size posed transportation difficulties, preventing it from fitting through a door. Additionally, task mechanism placement was out of the camera’s field of view, causing torpedoes to be fired through the thruster wash. An excessive offset in the center of mass and buoyancy also prevented the vehicle from achieving a downwards-facing orientation.
These issues helped shape the requirements for Talos. We used a decision matrix to down-select different concepts, ensuring the new vehicle would meet our needs through various design reviews. The new chassis was designed for manufacturing, allowing it to be fabricated easily.
Chassis Improvements:
- Material and Weight Reduction (Last Year): Talos improved rigidity while reducing weight by 2.7 kilograms by swapping the material to 6061 aluminum and selecting tall cross-sections to increase the area moment of inertia. The structure is arranged in triangular shapes interconnected with steel tensioning cables, and all assemblies underwent FEA simulations to verify structural integrity.
- Modular Task Mechanism Mounting System (Last Year): The new chassis integrates a modular task mechanism mounting system into the structural beam below the hull. This location ensures the thruster wash does not interfere with the task mechanisms. With the new chassis, the width of the vehicle was reduced by 54.7%, enabling it to easily pass through a doorway.
- Improved Maneuverability (This Year): Drag from the thruster cables was reduced by shortening the cable path and fabricating a new lid for the cables to come out more streamlined to the vehicle. Improvements to the center of mass and buoyancy locations made more orientations possible. Adjustability in the center of mass location was allowed by shifting the batteries forwards and backwards on indexing rails. This new mounting system allows the batteries to be positioned repeatably and they snap in with compliant clips allowing for fast, toolless swapping.
- Buoyancy Adjustments (This Year): Buoyancy foam is located in between the hull and on the bottom beam to adjust the displaced volume of the vehicle. This year’s buoyancy additions can be seen in the image below, highlighted in blue.
One of the significant mechanical enhancements in Talos’ design is the advanced torpedo launcher and marker dropper mechanism, integrated with redesigned servo housings. The previous 3D-printed servo housings were prone to leaking, causing damage to the servo motors and disrupting the torpedo and marker-dropping systems. To address this, the team developed CNC-milled aluminum housings featuring two radial seals, improving waterproofing and enhancing tolerance to positional errors during mounting.
To avoid pitching downward and risking the loss of Doppler Velocity Log (DVL) tracking, the torpedo and marker dropper system was split, with torpedoes pointing forward and markers pointing downward. This was achieved using bevel gears to transmit torque between the upper and lower sections. The new design maintains the simplicity of a single servo mechanism while allowing Talos to perform precise marker drops and torpedo launches without unnecessary movements, ensuring robust and reliable task execution during underwater operations.
In addition to the torpedo launcher and marker dropper, a new claw design was developed to enhance Talos’ capability for tasks requiring object manipulation. The claw, designed to easily detach from Talos, operates with a single servo and utilizes a rack and pinion mechanism. The claw is mounted at a 45-degree angle, determined to be optimal for grasping various objects in underwater tasks. The design includes interchangeable and customizable fingers, allowing the team to adapt the claw for different objects it needs to handle. With a maximum grip strength of 42 N per side, the claw provides robust and reliable performance for object collection tasks.
In the image below, the servo housing is silver, the torpedo launcher is scarlet, and the marker dropper is grey.
To enhance Talos’ ability to perform tasks requiring precise downward orientation and object detection, we integrated a new Downward-Facing Camera (DFC) system. The DFC is encased in a robust external housing made from aluminum 6061 and polycarbonate, providing protection from the harsh underwater environment while maintaining a lightweight structure. Externally mounted due to space constraints within the main hull, the DFC’s placement optimizes the camera’s view of the area directly below Talos. The housing features precision seals and high-quality O-rings to ensure waterproofing, and includes internal damping materials to absorb shocks and vibrations.
The DFC’s modular design allows for easy assembly, disassembly, and upgrades, simplifying maintenance. Securely attached to Talos using custom brackets and mounting points, the camera remains stable and accurately positioned during underwater movements. This precise positioning and robust protection enable Talos to perform tasks like marker dropping and object collection with high accuracy. Overall, the DFC’s design significantly enhances Talos’ capabilities, contributing to our strategy to excel in the Robosub 2024 competition.
Enhancing the operator experience has been a key focus for the Mechanical Subteam this year. Recognizing that ease of use and efficient maintenance are crucial for successful underwater missions, several improvements were implemented to make Talos more user-friendly and manageable.
1. Turnbuckles for Tensioning Cables
The tensioning cables used in Talos’ structure were upgraded with turnbuckles, allowing for quick and easy adjustments. This improvement ensures that the tension can be fine-tuned or completely released without disassembling the entire AUV. The ability to easily adjust the tension helps maintain the structural integrity of Talos and simplifies the setup process before each mission.
2. Replacement of Square Tubing with L Channels
Square tubing on the front and back of Talos, used for task mechanism mounting, was replaced with L channels. This change prevents screws from being accidentally dropped inside the tubing during maintenance or assembly. The L channels provide the same structural support while reducing the risk of losing small components, streamlining the assembly process.
3. Upgraded Battery Housing Rods
The threaded rods that held the battery housings were thickened from 8-32 to ¼-20. This upgrade prevents bending during transport and repeated use, enhancing the durability of the battery mounting system. The sturdier rods ensure that the batteries remain securely in place, reducing the risk of electrical issues caused by loose connections.
4. Tether Spool
A new tether spool was designed to manage the AUV’s tether more efficiently. The spool features an Ethernet slip-ring, allowing the tether to be wound and unwound without torsional strain. This innovation has significantly increased overall system reliability and eliminated the need to disconnect the AUV to extend the tether length, making setup and deployment quicker and more straightforward. The tether spool is shown below.
5. Color-Coded SubConns
To prevent misconnections, color codes were added to all SubConns. This simple yet effective improvement ensures that operators can quickly and accurately connect the various components of Talos, reducing setup time and minimizing the risk of errors.
6. Rubber Bumpers
Rubber bumpers were added to all thrusters and battery housings to avoid injuries and damage to pools. These bumpers provide an additional layer of safety for both the operators and the equipment, ensuring that Talos can be handled and deployed safely in various environments.
These improvements collectively enhance the operator experience by making Talos easier to assemble, maintain, and deploy. The focus on user-friendly design ensures that the team can operate Talos more efficiently, dedicating more time to mission-critical tasks and less to troubleshooting and setup.
Improved Tether Spool
The team’s previous battery housings have been implemented on UWRT’s AUVs since 2017. Due to the age of the old housings, mechanical failures occurred at the sealing surface due to worn out gaskets, inconsistent sealing due to installation error, and poorly secured pressure relief valves. The team saw the need to replace these housings as an opportunity to improve upon the entire system.
Mechanically, each of the smart battery housings were CNC milled from aluminum blocks with iso-griding placed on each lid to reduce the total assembly weight, including electronics, by 0.68 kilograms. The lid is secured to a sealing face with an o-ring, generating a more reliable seal. This allowed the housing to only be opened for maintenance which reduces the possibility of the seal falling from installation error. Each battery housing features a window to view a visual display, allowing an operator to obtain information about the battery state. Battery hulls are fitted with a pressure relief value for safety and with two SubConns for power and telemetry.
The new layout of the Mark 2 electronics required a complete redesign for the electronics housing. The original goal for designing Tempest’s housing was to reduce the number of steps it takes to access the electronics. That vision was not fully realized through Tempest. The old electronics housings were secured on the rails through dovetail slots. This allowed for consistent alignment front to hull but not starboard to port.
In the electronics cage redesign, a snap fit piece printed of TPU was designed to both provide tactile feedback as well as consistent positioning. This design process for the new camera and board cages was considerably more collaborative with software and navionics, respectively. Navionics was able to send CAD files for each board. This allowed for better designing around connectors and other features.
The cages additionally added support for new features of Mark 2, such as improved cooling for the electronics as well as LED status strips to display vehicle state.
Safety Stack
A large portion of setup time for pool tests was spent on assembling the robot network. The original setup required three individual components (router, switch, and wifi gateway) to be unpacked and connected. This time to set up as well as debugging errors that occurred from wrong connections cost precious time during the pool test.
The safety stack was developed out of a DeWalt box, with a custom designed interior frame to hold the necessary electronics together. These hold the network switch, router, and a Raspberry Pi with a touchscreen to connect the stack to the internet. A second Raspberry Pi was added to connect to a handheld kill switch and stack light. This Raspberry Pi connected into the vehicle network to allow for the vehicle to be remotely killed from the side of the pool. Additionally, the stack light showed the current vehicle’s kill and movement status to the swimmers and other observers.
The safety stack simplifies pool side setup, only requiring power and the vehicle tether to be plugged in. The software team’s laptops can then connect either over wireless or the Ethernet ports on the top of the stack to manage the vehicle. This has been a staple at all previous pool tests, simplifying the packing and setup, and will be an important tool to bring to RoboSub.
