Preliminary Detailed Design
This page documents our Preliminary Detailed Design process. At the end of the previous phase, Systems Design, we had narrowed down our design concepts and selected the Rotational Spring System with Digital Data Acquisition. This design consisted of a hydraulic piston pushing against a set of springs, which were attached to a wheel that could be rotated to select springs for different aircrafts.
The first step of the Preliminary Detailed Design review was to start doing calculations. In particular, these calculations involved coming up with the appropriate formula for the spring constants and then creating a MATLAB script to easily output them.
During this process we discovered that the spring wheel concept was not viable, due to both torque applied to the wheel and the size of the wheel. Instead, we moved to a cartridge system where the springs are held in a small container that can easily be switched in and out of the system. Using these ideas and calculations, we created a prototype of our design.
Team Vision for Preliminary Detailed Design Phase
After meeting with the customer, the team determined that the scope of the project was not as large as originally thought. However, the team intends to exceed expectations, resulting in the plan for a twofold digital test system with an analog backup in the case of unexpected constraints and challenged.
The team planned to complete the following steps:
- Determine the designs for the Proof of Concept (POC)
- Build the POC
- Test the POC
- Calculate and design the details for the AABS
The team completed the following:
- Explored and determine the cartridge design
- Developed prototype calculations for pressure displacements
- Developed and delivered training for all non-Mechanical Engineering team members
- Narrowed the two POC spring models and did the calculation for each
- Constructed POC
The team employed basic mechanical engineering knowledge to simulate the provided pressure-displacement curves. Through knowledge of system dynamics, dynamics, and scaling factors, the team created formulation to find the preferred components. This process was then automated through the usage of MATLAB. The following assumptions were made during the analysis.
- Ideal springs - Constant k-value, no deformation, massless springs.
- The springs will not buckle.
- The rod will not buckle.
- Negligible friction.
- Uniform cross section of piston housing.
These assumptions will be relaxed as the analysis is further developed.
- The rod was proven analytically to not buckle.
Refer to Proof of Concept Analysis section for detailed analysis implementation.
Through scaling the provided displacement and input pressure, the team was able to create a Proof of Concept intended to output a pressure-displacement curve to complete the final customer requirement. This Proof of Concept is intended to supplement the analysis made for the final design to provide security and confirmation that the proposed system will work.
The team will show reasonable caution for the testing of the Proof of Concept. This includes protective eyewear, a controlled environment for testing, and appropriate physical distance between test members and the prototype. Additionally, we made sure to not be standing in the line of sight of the pressure chamber in the case of pressure leakage. At the initial test, the pressure cap caused a leakage in the chamber. This test was performed in an engineering laboratory. After discussion with a Subject Matter Expert, the team learned that the chosen PVC was not a suitable material for compressed air. Due to this, the team plans to reconstruct the POC using a suitable pipe and perform the test plans.
Safety measures for the final design will be based upon findings from operation of the Proof of Concept as well as analytical calculations and expectations.
Ideally, the POC and final design will undergo one use scenario, which is successful simulation to collect data. In the event this does not happen, the following precautions are noted with Use Scenarios.
- Air does not bleed properly.
- If primary or secondary inspection reveals that the system is not entirely bled of air, the user will tap on system in order to loosen air bubbles. They will then wait between 4 and 24 hours to check air bleed again, depending on time constraints.
- If the system is not entirely bled of air after a third inspection, the user will contact maintenance that will then restart the system.
- Test parameters are not met.
- The user will attempt to troubleshoot using the provided manual.
- If troubleshooting may be solved by a solution in the manual, the user will perform the required maintenance and attempt again.
- If the troubleshooting error is not addressed in manual or if the manual solution does not work then the user will contact maintenance or a technician who will reset the system.
- Pressure causes system leakage.
- The user will immediately switch off the system and safely inspect the leakage.
- If leakage is found at a component level, the component will be replaced.
- If source of leakage is not found then maintenance and technician will be contacted.
Following testing and analysis on the POC, lessons learned from the fabrication and test processes will be ported to our final design. While the POC utilizes linear springs, the final design and cartridge assembly (as discussed in Design and Flowcharts) will utilize spring discs, for their compactness and high stiffness to height ratios. As such, a series arrangement of parallel stacks of spring discs will be used to supply resistance to the piston in the final design.
Prototyping: Feasibility, Analysis, and Testing
- Validate AABS system architecture ideas by replicating analogue of spring disc compression with linear springs to exaggerate representative spring disc compression.
- Evaluate and alleviate system flaws by conducting test piston extensions on proof of concept prototype
- Draft a list of lessons learned for implementation on final AABS design
- Construct prototype test plan and safety guidelines for use on POC and future AABS testing.
Proof of Concept
The first prototype created by the team is a small scale Proof of Concept towards the proposed design. The team believes that fabrication of a prototype will reveal problems that may have been missed in engineering analysis.
Upon searching for commercial springs to use, the team realized that Case A would be overly difficult to create due to the following problems:
- Both springs would have to be held at a horizontal plane through some manner.
- The magnitude of Spring 1 must be magnitudes less than Spring 2 in order to have two distinct compressions, rather than the two springs acting together in series.
As a result, the team planned to only implement Case B in the POC. Note that the final design utilizes Case A, with spring discs as opposed to linear springs. Due to the similarities between spring discs and linear springs, their behavior is related via Hooke's Law and thus the POC serves as a useful metric for the feasibility of the final AABS design.
Buckling CalculationsBuckling occurs when a shaft deforms under high loading. Buckling calculations are performed to ensure that shafts/rods/etc will stay rigid throughout testing. Calculations for the POC Rod are shown below.
- Round aluminum stock was lathed to size
- Detailing was done on the piston head using a parting tool to create groove for O-Ring
- A hole was drilled in the center of the piston and threaded
- Shaft was cut to size and threaded
- PVC was cut to size
- PVC cap was drilled for bike pump air valve
- Spring housing was 3D printed
- Bases for the PVC were 3D printed
- Piston heads were threaded onto the shaft
- O-Ring was added to piston head
- Assembly was put into PVC with lucubrating oil
- Bases were added to PVC
- Cap was attached to PVC with epoxy
Bill of Material (BOM)The BOM is a compiled list of raw materials, subassemblies, and top-level assemblies used to track the components used to manufacture the full assembly. It includes the cost of the components, along with the vendor and the product number assigned by the vendor for convenience in case a component needs to be ordered again. The POC BOM only includes components manufactured or bought for the sole purpose of building the POC.
POC Budget and BOM
Preliminary AABS Design Budget and BOM
Included in this section is also a preliminary BOM for the final design, based on cost estimation of sensor likely to be used. This is also useful in performing a more detailed cost analysis. It should be noted that this is a preliminary BOM, and is subject to change following any changes in the final design.
Once the Proof of Concept is completed, the following test plan will be performed.
- Position the blocks as specified by spring lengths as noted.
- Pressurize the tank to approximately maximum pressure ~90-100psi.
- Record pressure measurement off bike pump gauge as well as displacement with dial caliper.
- Using valve, decrease the pressure with small increments. Record pressure and displacement measurements.
- Repeat until piston is no longer pressurized.
Data AcquisitionData acquisition for the Proof of Concept will be performed with a dial caliper for displacement and the bike pump pressure gauge for pressure measurements. We will be collecting data manually. As shown in the above schematics, the piston during force application will push out the steel rod concentric with the spring assembly. This displacement will be measured.
PurposeDemonstrate objectively the degree to which the Engineering Requirements are satisfied, namely the ability to customize the pressure v. displacement curve provided from the prototype cartridge design of the prototype. This is Meggitt's most important concern as stated in our presentation April 5th.
Design and Flowcharts
Cartridge UseThe cartridge subassembly will be used to mimic the entire three sloped nature of each desired brake category. Meggitt has specified a total of six types of brakes, ranging from 'small jets' to large commercial jets. With each increase in brake size, the displacement and expected spring constant (K) increases, necessitating a larger assembly footprint. As such a larger amount of spring discs will be used for each consecutively larger brake design. Note that the cartridge assembly is designed such that one can be easily subbed out for another. Simply remove one of the screws holding the crossbar in place, rotate the bar out of the way of the cartridge slot, and remove and replace the installed cartridge. Ensure the piston is not pressurized during cartridge replacement. Following our design presentation with Meggitt, the customer expressed a desire to have a completely variable cartridge design, capable of replicating any 7th curve. As such the spring disc configuration will be further designed to utilize solely commercially available equipment. A technical manual in conjunction with an Excel or MATLAB based program will prescribe the stiffness of the spring disc setup required for any curve, given pressure input and desired displacement.
Safety ConsiderationsThe base plate of the cartridge house and hydraulic cylinder assembly is designed to constrain the assembly to allow for a static state only. This design will likely be altered to completely enclose the cartridge design following ANSYS simulation and deflection analysis in the upcoming phase. A polypropylene (PP) medium-hard enclosure will encase the AABS system within the cart to ensure, in the event of rapid unplanned disassembly, any subassemblies or components do not escape the footprint of the cart. Additionally the system utilizes both an air-bleed valve built into the hydraulic cylinder and a micrometer valve connected to the graduated cylinder design as discussed above.
HydraulicsNote the two hydraulic lines into the hydraulic cylinder. The leftmost line is the fluid in. This line travels through a pressure transducer before reaching the 0.052" restrictor and 3/8" fluid inlet. The right most line is the fluid out. This line is connected to a valve serving a dual function. First, this fluid can be released for the completion of a digitally run experiment. Second, the valve allows for use of the analog graduated cylinder method of data extraction as mentioned above. Both methods can be run simultaneously.
During this phase we added five new risks. Three of these involved testing the prototype: the piston housing exploding due to pressurized air, leakage due to poor seals, and the design not giving the curve we expected. The latter is most critical for the design itself: if our model is wrong, we have to start over from the beginning. This is why we're making the prototype in the first place. The first risk, the piston housing exploding, is the most critical in terms of danger to the operators.
The other two risks involve the springs themselves. When calculating spring constants, we found that the displacement of the spring and the spring constant are inversely proportional. If we try and decrease one, we increase the other. This is leading us towards spring disks, however those are very small and require precise sensors for measuring their displacement.
After reviewing the entire list of risks, we decided to update a few of them. The first change is setting the likelihood and severity of the spring wheel not locking in place to 0. This is because we removed the spring wheel design entirely. The second is the size of the simulator. The test springs we're using for the prototype are a foot long, and it is likely that they will be larger for the final design. We are mitigating this risk by switching to spring disks, but it is still important to keep aware of.
The last update is to the newly added risk: the explosion of the piston housing for the prototype. We created the prototype with PVC pipe, as it was the right size and easily accessible. However, we learned shortly before testing that PVC pipe is not rated for compressed air. If we had attempted to pressurize our prototype to 100 psi, the pipe would have shattered and sent shrapnel flying. This would have been incredibly dangerous, and we are thankful to the professor who warned us in time. The likelihood of the risk therefore increased, though once we replace the PVC with aluminum, the likelihood will go back down again.
Design Review Materials
Preliminary Detailed Design Review as presented April 5th 2018. Meggitt's Kyle Berkowitz and Ankit Prasad were in attendance in addition to the team's advisor Harold Paschal.
Plans for next phase
- Elias's P4 3 Week Plan
- Evan's P4 3 Week Plan
- Lily's P4 3 Week Plan
- Mike's P4 3 Week Plan
- Tony's P4 3 Week Plan
- Garrett's P4 3 Week Plan
- Sabrina's P4 3 Week Plan
- Lori's P4 3 Week Plan