Project Milestones & Overall Schedule

End of first semester goal

By the end of the Fall 2021 semester, our baseline goal for the project is to be in a position to immediately begin construction of the specified minimum viable product without any additional design work. This would require the full development of technical engineering drawings, CAD models and assemblies, wiring diagrams, hardware specifications, a complete bill of materials, and a well-defined plan of operation (e.g. what controller actions will elicit what functions of the robot). 

We also identified a more ambitious, but still realistically attainable upper bound on our progress this semester. This goal would be to have constructed and begun testing a functional prototype of our robot embodying the functionalities of our minimum viable product. These include the ability to navigate in water as well as on land, and to move between the two mediums. Of course, this would include completing all of the tasks set forth for the previous goal, but with the added challenges of fabricating, assembling, validating, and testing our design.

First Semester Accomplishments

With respect to the team’s accomplishments from the first semester, this can be categorized into Project Management and Sub-Team specific accomplishments.

Project Management:

  • Given the open-ended nature of our project, the team drafted Project Proposals to highlight the interests of each individual team member when determining the final project for our Senior Capstone.
  • The team defined a Team Contract to ensure effective communication / collaboration amongst our members.
  • Defined sub-functions that we wanted the robot to entail. However, given the feasibility challenges presented by numerous sub-functions, the concept of a Minimum Viable Product was introduced.
  • The team brainstormed a series of proposals to highlight the functionalities of the robot’s MVP, including specifics of the Land Movement and Water Movement features.
  • Utilizing the brainstormed similarities amongst each of the MVP Proposals, the team finalized the designs for the Land Movement and Water Movement functionalities.
  • The team has divided into sub-teams including Legs, Wheels / Treads, Hamilton Jet, and Buoyancy. Thus, throughout the upcoming weeks, the sub-teams worked on aspects of the functionality.
  • With the knowledge the team has gained from our designs we have presented and internal Design Showcase in which each sub-team presented their individual design parts in tangent with the MVP, Impact on Stakeholders, and our design process.

Sub-Team:

  • The team split into sub-teams to begin further research / design work for the functionalities of the robot. The sub-teams included: Swim, Buoyancy, Wheels / Treads, and Legs.
  • Swim
    • Determined that the robot’s Swim mechanism should be modeled based on a Centrifugal Pump.
    • Determined the appropriate dimensions for the Centrifugal Pump (intake / outtake diameter, casing height, casing diameter) by modeling the robot’s hull as a rectangular prism and determining the drag force of water across the robot.
    • Using an assumed intake velocity, the respective outtake velocity and rotational velocity of the impeller was calculated to determine a feasible motor.
    • The components of the Centrifugal Pump were designed utilizing Fusion 360. These components included the intake / outtake, impeller, casing / casing cover, and motor shaft.
    • The Fusion 360 design components were iterated on utilizing the finalized pump dimensions.
    • The Swim sub-team tested the Centrifugal Pump by spinning the motor shaft and determining whether a pressure difference was created. The pump worked successfully, and a video can be seen here.
  • Wheels / Treads
    • Determined design for integration of drive assembly into the lower leg assembly
      • Off-axis rotated motor assembly with miter/bevel gears to change axis of power transmission
    • Determined designs for track shape, sprocket type, and suspension type (D-shape, M-type, and modified Christie suspension)
    • Selected a motor to power the legs and tracks (Brushless DC motor with planetary gearbox – 24V 430RPM – stall torque of 1.7 Nm)
      • Determined relative gear ratios to meet design metrics and constraints regarding the maximum angle of attack and minimum level-ground speed
    • Begun high fidelity CAD for drive sprocket, integration assembly, suspension-spring column, structural spar, and roller wheel bracket
      • Including specification of fastener types, bearings, spacer dimensions
      • Selection of material types and parts for 3rd party sourcing, 3D printing, and in-house manufacturing
      • Designing with anticipation of required tools and manufacturing equipment – aiming to minimize part complexity by constraining ourselves to the minimum number of machines needed per part
  • Legs
    • Decided on a leg with two distinct sections and one “knee” joint connecting them
    • Decided to utilise a telescopic leg design to improve the efficiency of space usage while folding the legs. 
    • Determined suitable sizes for the leg sections to achieve the desired maximum ground clearance at full extension of the legs
    • Determined the minimum torque requirements of the motors needed to actuate the joints (both “hip” and “knee”) based on the 40 kg robot weight and maximum lever arm length of the upper leg section
    • Anticipated the need to design and implement a 10:1 gearbox to develop the minimum torque determined previously 
    • Determined where the “knee” motor and gearbox should be located to ensure power transmission to the knee does not interfere with full bending or infringe on the space requirements of the wheel and tread motor
    • Created and iterated CAD models of the leg sections, 3D printing to gain a better understanding of the folding motion of the leg
    • Identified viable components to purchase for the gearbox, purchased one potentially viable motor for prototyping and testing.
  • Buoyancy
    • Determined the appropriate dimensions for the reservoir volume as well as the bilaterally symmetric reservoir placement.
    • Purchased the Peristaltic Pump, CO2 canister, air tubing, solenoid valve, float bag, and pneumatic connecting fittings
    • Determined the Peristaltic Pump flow rate and by testing found the maximum hydrostatic pressure the pump could withstand.
    • Fusion 360 design components of the buoyancy system which include: reservoir system, lift bag system, and CO2 canister holder

Winter Interim

If group members have ideas or important design concerns, we can set up times for full team Zoom meetings. If possible for a sub-teams to complete machine drawings, finalize Fusion 360 designs, and more this would also be when they are done. Nothing is required during this time but we should be keeping our minds fresh on the project details. 

Initial End of Year Goal

We at HARRT have determined that a Minimum Viable Product (MVP) is necessary, primarily as it guides the functionalities of the product specifically towards those that solve relevant customer pain points. By having multiple unwanted features, it may be challenging to validate the usefulness or benefits of the product. Essentially, this means that early stakeholders and customers of the product are presented with a simpler version of the product that solves their most pressing pain points. Additionally, given the time constraints that the HARRT Team is presented with (1 academic year to have a final version of the product), having a contained set of features will ensure a faster release of the product and early validation testing such that changes to the existing features can be made and additional features can be added.

To determine the product requirements that would be part of the MVP, the team initially completed Written Proposals in small groups, which included content describing what they felt would be beneficial to include in the final MVP. Upon substantive discussion of the benefits and drawbacks to each design, the team came to the design conclusion as described in Our Solution.

By the end of our second semester, we should have a completed product that incorporates the functions defined as part of our Minimum Viable Product (MVP), satisfied the target methods and constraints, and advances the state-of-the-art model of amphibious robotics.  Specifically, its goal is to ensure that the product is usable for early customer testing who can then provide feedback for future iterations of the product. 

For the Water Movement sub-function, the Hamilton Jet was chosen as it is highly advantageous in comparison to alternative Water Movement designs (e.g. propellers, biomimetic design) given it’s reliability due to relatively few moving parts and it’s steering nozzle that is designed to minimize thrust loss when navigating at various angles. For the Land Movement sub-function, we selected a hybrid system of legs that use wheels or tracks as their end effectors. This was justified by the desire to advance the definition of versatility in current state-of-the-art robotics research. After conducting an in-depth Literature Review, it was determined that the legs would offer superior mobility across abnormal terrains encountered in high obstacle density environments while the wheels and tracks would offer greater efficiency in more regular environments.

Updated End of Year Goal

When conducting our routine progress check-ins, the team determined in early spring that our ambitious goals were, unsurprisingly, presenting more challenges than we were able to anticipate. Reflecting on the rate of progress for each sub-team, we dynamically readjusted our long term goals to better reflect the limits of our abilities without compromising on the broader goals of the project, including our desire to learn new skills, take pride in our produced work, the hope of creating physical prototypes.  From these conversations, we broke the project into several levels: Level 1, Level 2, and Level 3.

At Level 1, we determined that each sub-team would remain largely independent. The primary focus at this level is to develop a prototype that meets all the individual requirements and specifications the sub-team feels necessary, based on the original goals for the overall robot.

At Level 2, the four sub-teams would begin integration by similarity. Treads/Wheels and Legs both are targeted at terrestrial locomotion and would thus work towards a unified Land Movement assembly. Similarly, Buoyancy and Swim/Propulsion focus on aquatic environments and would thus join their designs as part of a Water Movement assembly. The result of reaching our Level 2 goals would be two separate chassis based on these assemblies. Each chassis would be developed independently of any assumptions used for the other; for example, the Land Movement chassis would not be waterproofed at this level.

At Level 3, the Land Movement and Water Movement Assemblies would finally be combined into the final unified robot. Every aspect of integration would need to be considered at this point. As an example of some relevant concerns, all terrestrially-focused components would need to be waterproofed and all aquatic systems would need to be able to fit within the dimensions provided by the Land Movement teams.

Discretizing the project into these levels allowed the team to readjust our target for the end of the year. We determined that moving up a level involves increasing amounts of work; the jump from Level 2 to Level 3 is far more nuanced than the jump from Level 1 to Level 2. Judging from the rate we expected to reach the completion of Level 1, it became apparent that completing a Level 3 robot was no longer reasonable. As such, we endeavored to reach the completion of our Level 1 designs by late March, at which point we would begin testing our resulting prototypes and promptly move on to working towards our Level 2 goals. After this reflection, we remain cautiously optimistic that we will be able to achieve the production of Level 2 chasses, which we believe will aptly demonstrate a proof of concept for our ideas. Future teams and other groups of our stakeholders should be able to gain valuable information from our progress at that point, carrying it onto their subsequent endeavors.

Team Gantt Chart [ps2id id=’Gantt’ target=”/]

Gantt Chart Last updated: 4/20/22