Team Vision for System-Level Design Phase
Goals and Initiatives:
- Complete all deliverables on time
- Determine the existing state of the Robocomposter Structure
- Identify areas where the structure lacked integrity and functionality
- Identify the current state of the sensors
- Determine what sensors are critical, functional, and capable of being calibrated
- Identify the motor model and compare specs with requirements
- Begin composting to determine working recipes and composting time feasibility
With the goals above in mind prior to starting the systems design phase, there was a heavy focus on trying to determine the entire state of the Robocomposter to begin identifying areas that would need redesign, parts that would need to be purchased, and begin brainstorming a structure for controls integration. All deliverables were completed on time and are outlined in the sections below. Additionally, planning was done to coordinate efforts for programming and coding going forward so that controls and automation can be implemented before the final phases of MSDII. The mechanical components of the prototype were stripped off the platform and analyzed and the sensors were removed to determine their existing state. All documentation and analysis are outlined below in the Systems Design webpage.
A functional decomposition was produced to determine all vital functions that the end product will be capable of performing. The functional decomposition starts with the overarching goal of producing compost and delivering more specific functions to achieve this goal as the tree branches down.
The link to the live document can be found here
Although the hardware for the Robocomposter was solidified during the first prototype, it was thought to be worthwhile to benchmark in case there are any glaring improvements that could be made within the budget. To complete the benchmarking, the functional decomposition was utilized to break down the prototype into basic functions and then searching was utilized to benchmark technologies that could perform the objective better than what is currently on the prototype.
To compare the system concept designs against one another, a number of criteria were brainstormed. The concepts were based off of the engineering requirements and customer requirements and are as follows:
- Safety of components
- Impact on composting speed
- Ability to maximize size
- Durability of components
- Feasibility of constructing the components
- Cost of the components
- Educational value of the components
- Ease of use of the components
- Portability of the system (i.e weight)
Morphological Chart and Concept SelectionDriven from the customer requirements, the functional decomposition, and the benchmarking that was performed, the functions of the Robocomposter were established and input into a Morphological table. The Morphological table was then utilized to produce a Pugh chart where the existing prototype was set as the datum. Even with the benchmarking and brainstorming that was performed, the prototype came out with the highest score.
Feasibility: Prototyping, Analysis, Simulation
To test whether the existing motor powering the shredder of the prototype is capable of delivering the required torque, a calculation needed to be conducted to determine the mechanical requirements. Since wood is generally taken as being the strongest material to pass through the shredder, it was used as a "worst case" for organic material that might pass through the shredder. Calculations for torque and power were conducted during the first iteration of the design and repurposed to ensure that the motor used was within spec. Since one of the biggest concerns is the ability of the motor to granulate the material to expedite the composting process,a check was performed as is shown below.
To ensure that the existing motor could supply the required torque, the spec sheet was obtained. The link to the spec here
The key specs listed on the OEM's webpage for this motor is that:
- The motor can deliver 2180 oz-in or 15.4 Nm of torque
- This value is far less than the 60 Nm required to shear small twigs
- The motor is a stepper motor
- The motor has a 1/2" shaft diameter
In order to determine if the sensors needed to be replaced they were evaluated for the operating conditions expected within the reaction chamber of the composter.
The datasheets and information for the sensors can be located
Simple sensor request walkthrough and implementation requirements.
- Client-side webpage is loaded
- Webpage requests sensor data to Web client sends request to webserver
- Webserver uses a peripheral library to communicate with Raspberry Pi
- Raspberry Pi sends data request to Arduino
- Arduino receives request and processes sensor reading code
- Arduino then sends sensor data back to the Raspberry Pi over Serial
- Raspberry Pi receives data and processes it to send to the webserver
- Webserver then forwards the data to the client
- Client receives and displays the data
- Raspberry Pi Webserver
- HTML webpages
- CSS for webpages
- Web framework to contain webpages and html request code
- Raspberry Pi Interface
- Peripheral libraries to interface with Raspberry Pi GPIO/USB port
- Event handler code to transmit and receive serial data to Arduino
- Arduino Interface
- Event handler code to receive and transmit to Raspberry Pi
- Code to read data from sensors
The system architecture consists of 7 individual subsystems, the user interface, the Raspberry Pi, the Arduino, the sensors, the motors, the motor drivers, and the power systems.
- The User Interface is connected to the Raspberry Pi and the Power System, the Raspberry Pi sends output data to the touch screen and web client while they send in user inputs back to the Raspberry Pi. The power systems power the touchscreen with a 12V input.
- The Raspberry Pi is connected to the user interface, the Arduino and the power systems. The user interface uses interrupts to activate an event driven activation of the motors on the touchscreen and web client through a USB interface and Ethernet interface respectively. The Raspberry Pi gives IO information to the touchsceen and Web Client through HDMI and Ethernet respectively. The Arduino is connected to the Raspberry Pi using a serial IO connection and is controlled using interrupts, the Arduino then sends back data about the system. The power system sends 5V to the Raspberry Pi.
- The Arduino is connected to the Raspberry Pi, the Drivers, the Sensors, and the Power Systems. The Raspberry Pi sends interrupts to the Arduino to send data to the Raspberry Pi or to control the drivers. The drivers are controlled by an off or on signal from a digital output and sends back an output current from the drivers to allow the Arduino to protect the drivers programmatically. The sensors will send back analog to digital data which gives how the system is functioning. The power systems send 5V to the Arduino
- The Driver is connected to the Arduino and the Motors. The Arduino connects the relay to allow current to be sent to the motors, the current is then sensed and sent as a voltage to the Arduino. The motors will receive a 120V and max 10A DC or AC output. The power systems will give the needed 120V potential.
- The Sensors are connected to the Arduino and the Power System. The Arduino is sent digital and analog signals. The power systems give a variety of voltages to power the sensors.
- The Motors are connected to the Driver. The driver gives adequate power to the motors.
- The Power Systems is connected to everything that needs power. Each one gets a variety of voltages, the max current is related to the fuse box to which the power system is connected to ~15A.
Designs and Flowcharts
Empirical testing of composting was started to determine a feasible goal for composted material. To do this, 5 gallon buckets were filled with compostable waste in varying recipes. The recipes were documented and every couple of days, metrics and observations were documented in the spreadsheet found here