Team Vision for System-Level Design PhaseDuring the Systems Design Phase, the group plans to:
- Proceed with benchmarking against key parameters to ensure that the majority of design possibilities have been collected.
- Leverage a Functional Decomposition analysis to better understand the system’s core competencies and functions.
- Ideate basic, primary concepts for functional elements and systems-level designs.
- Investigate the feasibility and ergonomics of design
ideas through utilization of analytics, prototypes,
simulation, and benchmarking activities:
- Migration ramps for larvae
- Bottom layer removal system
- Micro-controller systems
- Compare design alternatives and refine scope of project through a Morph Table and Pugh's method of evaluation.
- Start a high level overview of the initial systems design concept and how subsystems will flow together in a complete system.
- Extend meetings with additional stakeholders to gather more information about everyone’s wants/requirements (especially meeting with Dawn Carter to discuss fly breeding).
- Finalize budget with the assistance of the
project’s guide and sponsors.
- Discuss all possible options available.
- Begin application for P2I Grant
Our overall work breakdown plan for the Systems Design Phase:
Functional DecompositionThe following figure illustrates the group's functional decomposition of the composting system, where items in blue represent functions outside of the control of the MSD team.
MaterialsSeveral materials were investigated for potential use in the composting unit. The materials were separated into metallics and plastics. The cost, stiffness, yield strength, density, manufacturability, hardness, corrosion resistance and transparency of the material were compared and are shown in the benchmarking table.
Link to our Materials Benchmarking Document.
Migration RampsA multitude of different BSFL systems were investigated in order to determine the benefits of different angles, materials, and roughness of ramps to be used to facilitate larvae migration to a pupation site. More in-depth information can be seen about each system in the linked document.
Link to our Migration Ramps Benchmarking Document.
Control SystemsThrough research and discussion among group members, control devices have been narrowed down to two controllers: Raspberry Pi and PLC. Both options have advantages and disadvantages:
- The Raspberry Pi is an affordable option and offers data logging but has limited capability of controls and is not highly suitable for shed conditions.
- The PLC is designed for controls and is suitable for conditions in the shed but can prove to be costly and needs extensions for long term data logging.
Link to our Control Systems Benchmarking Document.
Bottom LayerThe document shows more in-depth information into each of the designs in the table. Comparing all the proposed systems with the current system shows that the dual guard system, sloping, and the tumbler have the most positive attributes compared to our current system. The dual guard system is a design created by the team and will be discussed in further detail in future sections. All of the other systems benchmarked here could work theoretically but do not ideally meet all customer requirements, which are shown in the table as negative signs.
Link to our Bottom Layer Removal Benchmarking Document.
To select a concept to move forward with, the team created a Morphological Chart to display all possible solutions to the problems outlined in the Problem Statement and constrained by the Customer Requirements. The chart can be seen below.
Concept DevelopmentThe following images represent the concepts developed by the team through use of the morphological table. Members of the team ideated several design solutions based upon knowledge surrounding different functional elements of the composter system.
The first of these initial design alternatives include the Two-Guarded Scissor System and the Churner. Upon consideration of these concepts, the team identified that the Two-Guard Scissor System would be easy for a single operator to use. Its main drawback, however, is that it may prove challenging to manufacture and support. The Churner design alternative was noted by the group to be effective at simultaneously allowing for larvae migration and liquid removal. The design's tradeoffs include potential ergonomic issues for the operator and that it would most likely disrupt the processing of waste inputs (since all layers of food would essentially be mixed together).
Additionally, the group developed two other alternatives: the Two-Guard Bin, and Sloped Wall with Hatch. The Two-Guard Bin design would provide a simple, manufacturable design that is similar to the current state (offering some familiarity to the operator); however, it does not allow for optimal scale-up to occur and its risks are similar to those of the current state. The Sloped Wall with Hatch design was championed by the group as having the most optimal scale-up potential with respect to accommodating variable input load sizes. One of the major drawbacks noted was that since the design would prove to be more complex, there would be more risk associated with effectively building this concept.
The final design developed by the team was the Multiple Shelving Units concept. This design was identified to be easy on the researcher and relatively low risk (in that it basically utilizes multiple, small-scale copies of the current design). The main trade off with this design is that it is not a continuous system, which is an aspect that the project’s customer would prefer at this current time. Another concern of this design is that as the system requires more bins on the shelves, the work will become more cumbersome on the operator’s end (requiring more monitoring and interacting with several bins).
Link to our Initial Design Concepts
Feasibility: Prototyping, Analysis, Simulation
The Phase-Appropriate Feasibility Identification document allowed the team to understand what elements of system design must be considered and how to go about doing so. (Items in green represent those considerations that were successfully explored in this phase while items in red represent those that must be considered in the near future.)
Bottom LayerMethod 1:
Drawer: To test this process, compost was pushed through the current system. It would be ideal to replace this system.
Conveyor: Benchmarking showed this system is proven to work with BSF's and operates as a continual waste processing system. However, the paper does not clearly illustrate how system was designed. The team would need to start from scratch.
Churner/Centrifuge: Benchmarking said this design was not feasible. Parts must be continually moving, which is an energy cost. It would be hard to manufacture and has not successfully been built before.
Dual Chamber: Benchmarking said it has been done in several other composters; however, it is not really a continual process and it cannot be ramped up.
Multiple Shelves: Benchmarking determined this is feasible. It just requires cleaning out the composter after migration has occurred. This is the most common type of BSF composter.
Vacuum: The team discussed that they did not feel this was a feasible solution moving forward.
Door to the Bottom: Benchmarking determined it works well in worm composters. It has a low cost of materials and is easy to add food to. The team is unsure how it would transfer to BSF’s.
Tumbler: Benchmarking determined it’s easy to remove waste from system and base design already exists. However, might disturb larvae migration.
Dual Blade System: Solid Blade/Scissor Blades: We used experimentation to test this design using sheet aluminum and a plastic tub. This showed this design while still requiring some force was easier than the current one. However, more experimentation should be done as there are still several concerns.
To get a more detailed overview of the feasibility of each of these systems, see the Bottom Layer Feasibility Document.
Migration RampsMethod 1:
Inverted Ramps: This is the current design for the system and is proven to work with BSFL. It is not able to be ramped up in its current state.
The BIOPOD Plus: This is a system that’s on market for use with BSFL and is proven to work. There is no drainage system with this method and moisture content could inhibit migration.
Dome Composter: This system is proven to work with BSFL how ever it is not able to be ramped up from small scale to large scale.
Slanted Walls: The larvae are able to migrate up the ramps at angles less than 40 degrees. There could be a need for multiple exit locations for the larvae which could lead to a higher likelihood of larvae escape.
Double Grooved Ramp: The larvae would be able to migrate up the ramp wet or dry potentially with the assistance of grooves. The concern be with the depth and location of the ramps.
Control SystemsMethod 1:
Raspberry Pi: Suitable for this process as it has the capabilities of data logging, condition monitoring, and limited control. Number of GPIOs are limited and are not extendable with analog signal can take multiple GPIOs.
Arduino: Microcontroller is suitable for this process as it has the capabilities of data logging, condition monitoring, and limited control. Micro Controller not suitable for such conditions and requires to design an Enclosure.
MSP430: This particular microcontroller is suitable for this process as it has the capabilities of condition monitoring, and limited control. Program is not user friendly as the design is individualized.
PLC: PLC is designed for operations that require monitoring and controls. Addition of HMI will implement more control on system. Costs for a good PLC can range to high numbers. Long term data collection without HMI requires high level knowledge.
To get a more detailed overview of the feasibility of each of these systems, see the Control Systems Feasibility Document.
Concept EvaluationThe first Pugh chart below evaluates the top proposed designs by comparing them to the current design. The team chose selection criteria that was believed to best capture the customer requirements of the system. These include being easy to manufacture as well as safe and ergonomic. This makes it easy to build and handle. The team also included the size and variability of the composter so that it can fit in the shed with the desired load.
The first Pugh analysis yielded that the sloped wall system had the most positive attributes with the two guard systems and multiple shelves following close behind. Because of this, the team decided to remove the designs where "No" is present in the "Continue?" row and re-do the Pugh analysis using the scissor design as the new datum.
This second Pugh, again, yielded that the sloped wall design was the one with the most positive attributes. It was, therefore, selected as the team's proposed final design.
Systems ArchitectureA visual representation of interactions across subsystems within the proposed composter system has been provided below in the form of a Systems Architecture.
Above is the proposed final design for the composter system. The team utilized a design with sloped walls that can dually act to ramp up the system and be used for larvae migration. Larvae will be collected in a bin that is dried out so that they cannot escape. The group will utilize one of the two forms of the dual guard system, which will be determined in the next design phase, and collect the frass in a bin below the system. The system will either need to be indented into a table or will need legs attached to it to suspend it above the table. The whole system will have a lid in order to keep larvae in the system.
- Hold enough larvae to process 6kg of waste per day. The team performed rudimentary calculations and it proved that there would be enough volume to do so, but they plan to investigate this further in the next phase.
- Be easy to remove frass/waste: The group performed a basic experiment of this bottom layer removal system that showed it was easier than the current system. An improved prototype will need to be made in the next phase.
- Microcontrollers: The team needs to identify which would be the best for the system and maintaining proper temperature and humidity levels. This needs to be further investigated in the next phase.
- Larvae Migration: Experiments were completed as to prove this method of migration. More tests need to be done in the next phase with angles and materials. This will inform the final details of this subsystem.
Risk AssessmentThe Risk Assessment Matrix (developed in the Problem Definition phase) has been updated to reflect the current risks considered in the Systems Design Phase. These updates, made based on conducted experimentation with basic prototyping, can be found in the below table:
From the above table it is important to note that two risks were effectively mitigated and thus, removed from consideration. These include RRS3 (Losing an IE/BME student) and RSO1 (Societal norms of composting not accepted).
As shown in the below figure, the impact of several other risks was lessened by the team. No additional risks were developed at this time; however, careful consideration will be made in the future to continually capture other concerns.
Design Review MaterialsLink to our Design Review Agenda.
Link to our Systems Design Phase Risk Matrix Document.
Plans for next phase
During the Preliminary Detailed Design Phase, the group plans to:
- Create a preliminary design of the systems individually and together.
- Continue prototyping selected system in order to further analyze feasibility and challenges of the proposed design.
- Perform validation through calculations in an effort to ensure that the size and strength of the composter are adequate per project/design requirements.
- Create an initial 3D rendering of the proposed systems as well as a simulation of how the subsystems function together.
- Make a final decision using benchmarking and research to select a Microcontroller or PLC for the climate monitoring system.
- Begin planning out what will go into the shed and where it will be located.
- Create a Test Plan to ensure that all engineering requirements are met or exceeded.
- Continue updating the risk assessment matrix to ensure that the proper attention and mitigation strategies are in place (so as to minimize the impact of potential risks).
- Develop a Bill of Materials to ensure that the project is on budget and all required materials will be purchased.
- Pursue financial support through application for a P2I Grant.
Our overall work breakdown plan for the Systems Design Phase:
- Our Project Plan for the Systems Design Phase.
The construction of the shed is behind schedule and will require additional resources in order to be completed within a reasonable timeframe. Time will be afforded from the detailed benchmarking, as the line items associated with this activity (benchmarking and feasibility analysis of the bottom layer removal, migration ramp, and climate control systems as well as material benchmarking) have been almost entirely completed already.