P16421: Robo-Composter
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Subsystem Design

Table of Contents

Team Vision for Subsystem Design

This phase was extremely productive for the team on all fronts. After the System Level Design Review, we had planned on getting our overall layout nailed down and to start modeling each subsystem in a 3D modeling software. Additionally, the team was hoping to select and purchase a few sensors and start getting benchmarks in an initial compost bin. Last was the generic design of the wiring and signal routing as well as selection of the controllers that we will be using to display data and receive and control environmental variables.

The team assembled for an extensive brainstorming session on a Saturday in order to gain a strong foothold of what we are dealing with and how was actually can get it to work as seamlessly and efficiently as possible. During this meeting, we quickly came to the realization that our initial thoughts on system flow were simply not going to work due to the space restrictions. As a result, we took some of our other concepts from our morphological chart and combined them in a fashion that allowed for a horizontal flow of material as opposed to our initial vertical concept. Additionally, this meeting also allowed for our electrical engineers to gain a firm grasp on how everything would be routed from power to controller to sensors and back again. Throughout the next week, we fully modeled each component and assembled them in a preliminary frame. We made a few purchases of sensors and did some testing for how they would be hooked up. However, we have not yet begun testing in actual compost due to a few shipping delays. One final accomplishment that was not initially anticipated was making contact with the RIT community garden and gaining permission to use a barrel composter that they had on the side. Ideally, this will be where we do our actual testing.

Engineering Requirements

Feasibility: Prototyping, Analysis, Simulation

Gas Sensors

The methane, ammonia and oxygen sensors are non-contact sensors, so they do not need to be directly inside the main system of our composter. This is good because many sensors have operating temperatures that are below the expected temperature of the main system. Since the main system needs to have some sort of ventilation system, it would be best to place these sensors inside the ventilation system. There still may be some excess heat from the main system in the ventilation but nothing close to the maximum operating temperature of the sensors. The exact method is yet to be determined since the ventilation system has not been designed yet.

Temperature and Moisture Sensors

The temperature sensor can stand increased temperatures unlike the gas sensors. Therefore, it can be placed inside the main system. The mixer design would facilitate mounting the temperature sensor on the surface of the reactor chamber without being affected by the mixing blades. The same can be done with the moisture sensor.

pH Sensor

Currently, the there are multiple problems occurring with the pH sensor’s placement. First off, the operational temperature for most of the sensors we have found have been too low for what we need. Since it is a contact sensor it, will need to be able to withstand the temperature inside the main system. The next problem with the sensor is that it needs to be inside water in order to measure the pH, and the idea was to separate drainage tea and the main compost. An initial thought was to measure just the compost tea pH level to determine the overall pH. However, the drainage tea is thought to have a different composition than the main compost. Another idea for measuring the pH of the compost was to take the measurements manually via a pH kit that would come with the composter. This solution would take away the ideal scenario of no human contact to get information but would add a “learning” aspect to the device. Due to the high cost of the sensors that we found for the application, this is the direction we are leaning.
Sensor Plan

Sensor Plan

Screens

Screen Comparison

Screen Comparison

Drawings, Schematics, Flow Charts, etc.

Robo-Composter System

Robo-Composter System

Drawer and Grinder Assembly

Drawer and Grinder Assembly

Sectioned Drawer and Grinder Assembly

Sectioned Drawer and Grinder Assembly

Collapsed Drawer and Grinder Assembly

Collapsed Drawer and Grinder Assembly

Side View Drawer and Grinder Assembly

Side View Drawer and Grinder Assembly

Side View Collapsed Drawer and Grinder Assembly

Side View Collapsed Drawer and Grinder Assembly

Holding Tank

Holding Tank

Sectioned Holding Tank

Sectioned Holding Tank

Reactor

Reactor

Sectioned Reactor

Sectioned Reactor

Mobile Tank Wiring Diagram

Mobile Tank Wiring Diagram

Sensor Wiring Diagram

Sensor Wiring Diagram

Bill of Materials (BOM)

Material sources can be found here.

Risk Assessment

Risk Management

Risk Management

Plans for next phase

Over the next three weeks, we are hoping to gain a significant amount of data and ideally have data from at least one entire composting cycle. Peripheral systems will begin to be designed and the current design will be scaled back depending on the feedback received during the review with the client. Again dependent on the feedback from the review, simulations modeling stresses within components, mass flow, and heat flow will be developed in order to help us determine optimal materials and sizes or efficiently accomplishing the task at hand. We are hoping to have some materials purchased or at least priced out to some degree and have construction methods thought out in order to get an idea for how much machine time might cost us.

Revised Project Plan

Revised Project Plan


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