Preliminary Detailed Design
Table of Contents
Team Vision for Preliminary Detailed Design PhaseDuring this phase the team set out to work around the high risk design and purchasing items identified at the start of the phase. Those items included finding and purchasing a drive motor, a load system, and torque sensors that could meet the engineering requirements outlined in previous phases. The team also aimed to produce preliminary design documentation for both the electrical and mechanical systems.
As a result of the work done in this phase, some of the budgetary concerns identified were addressed. A sponsorship with Misumi was obtained and will be used to acquire the structural components needed for the rig. Talks with Futek are promising and may lead to the acquisition of torque sensors for little to zero cost. Volland has responded to inquiries regarding a drive motor with an option that fulfills our needs and is within our budget. The team is still considering options for the load system and are waiting to hear back from the vendors contacted. As shown on this page, the design documentation aimed for was produced and available for review.
Prototyping, Engineering Analysis, Simulation
Due to budgetary considerations, a significant amount of effort has gone into pursuing sponsorships for the high priced items. Futek, PCB, Volland, Placid Industries, Misumi, and Polaris have all responded with interest to sponsor at some level, and we are in the middle of on going communications with them. As of our most recent communications;
Polaris has offered a 5kW 3phase AC motor, which could be used as the system load.
Misumi has offered $1000 sponsorship of items from their website, as well as 30% off all future orders.
Placid Industries has forwarded the request for a particle brake to the president of the company.
Volland has provided a quote for a 5HP gear motor.
PCB Piezotronics has indicated interest to sponsor in an email last week, but has made no further communications.
Futek has selected a torque sensor based on our design requirements, and processing our request, we hope to hear back any day now.
The motor and sensors have been designed around the following power calculations, and the datasheets for the proposed motors can be found here. Motor Data Sheets
Sensing & Data Acquisition
According to the Futek sensor's datasheet, the torque sensors have a measurement resolution of 0.0133 N-m. This satisfied the engineering requirement asking for a resolution of 0.1 N-m or better.
As indicated by the Futek data sheet, the torque sensors measure up to 500 N-m of torque and represent the torque value using a differential voltage signal that is +/- 0-5V. To ensure the data being collected has a resolution of less than 0.1 N-m, a COTS 16 bit analog to digital converter (ADC) will be used for preliminary data processing.
The shaft will experience a maximum of 600 rpm or 10rps. To acquire data describing each rotation, a sampling rate of 100 Hz will be used. At this sampling rate, 10 data points will be acquired for each rotation.
The system is planned to use a Raspberry Pi as the controller and data acquisition unit from the ADC, meaning that it will have a complete picture of the system's behavior and state at any given time.
Once the Raspberry Pi boots, it will automatically launch the efficiency tester program. Once the program boots, it will check for the current speed of the shafts, making sure that the speed is 0 RPM. Although the program will boot with the relay drive pin set to not have the relay open, it'll wait until the shaft has returned to idle, just in case there was an intermittent power loss and the Raspberry Pi quickly boot back up.
The Raspberry Pi will then accept information about the test the user would like to perform via a Keyboard and Mouse through a graphical user interface. Parameters the user may enter here include shaft angle, diameter, type of coupling, and other mechanical parameters.
Once the user has selected to begin the test, the system will check that all interlocks have been closed. There are two interlocks, one on the door to the enclosure containing the shaft, and another on an easily accessible E-Stop. There will also be an Emergency Stop button the user may click on the interface. If any interlock is still open when the system is ready to begin the test, it will throw an error on the screen, allowing the user to correct the condition and try again.
Once the interlocks have all been satisfied, the system will briefly pulse the relay closed to allow the motor to spin for a short period of time. This will ideally spin up the shaft to a sufficient speed to check for equivalent speed on both ends of the shaft, ensuring proper installation of the shaft to the system. Once this check has been completed, it will begin the test proper, and allow the motor to spin up to full speed. While at full speed, it will be collecting data from the ADC and the speed pulses from the torque sensors. It will hold to a default duration for the test to perform, or less if the user commands it. Alternatively, the user will be able to select if they trust the system to collect enough information to end the test once the system has reached a steady state, or enough data has been collected for statistical significance.
Once the test is completed, the motor will be stopped by opening the power relay, and the system will wait for the shaft to return to 0 RPM. At this point, the system will save the data to an excel document, and ask if another test is to be performed.
This logical flow is captured in the flowcharts below.
Drawings, Schematics, Flow Charts, SimulationsBelow is a flowchart showing the control flow of the system. This will be the behavior of the system, and will guide the development of the finite state machine when the code is being constructed.
The following diagram shows the data acquisition portion of the system. This shows the power and signal acquisition concepts of the device, while using more specific pinouts and diagrams of devices.
BudgetingBelow is a breakdown of the team's allotted budget for each system. This budget breakdown is subject to change due to potential sponsorships.
The following breakdown is our preliminary BOM for any materials we can obtain from Misumi
Design and Flowcharts
DrivetrainThe goals of the system drivetrain are to:
- Never break
- Help minimize system noise to improve torque measurement quality
- Support R16, R17, and R18 halfshaft designs
- Minimize cost and complexity
Most of the risks to this project involve funding in some manner. Sponsorships are being sought out and negotiated with many companies in order to alleviate this issue.
Risks the team has begun to address:
- Not having enough funds to complete the project
- Many sponsors have been contacted
- FUTEK interested in helping with sensors
- Polaris interested in helping with motor
- Misumi will sponsor a portion of the project
- Alternative designs are being developed to use cheaper items
- Timeline risks
- Waiting on sponsorship puts the entire design cycle at risk
- Variation between designs based on what we can afford requires nearly a full rework of the test device.
- Multiple designs are being considered in a hierarchy depending on what resources are available
- Incompatibility with existing Baja designs
- CAD of current designs is being utilized in development of test rig
Based on interaction with sponsors and the development of alternative designs, the severity of several risk items associated with project budget were reduced. Continued interaction with potential sponsors also lowers the likelihood of issues arising. The long lead times associated with sponsorship does create some potential timeline risk, but that is significantly less severe than not having the funding for the project. Overall, during this phase the risk to the project has been reduced, but the priorities of mitigating these risk items has stayed the same.