P18371: Meggitt Brake Simulator
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Detailed Design

Table of Contents

In Phase 4, Team Spring Breaker confirmed that its proof of concept (POC) worked and from that, the team moved forward on its final detailed design. This phase content of our Edge page includes detailed information and outcomes of our journey through our detailed design phase (Phase 4). It also includes links to important documentation completed during this design phase.

Team Vision for Detailed Design Phase

In our last phase review, each team member developed plans for our next phase. Here’s a list of those plans:

  1. Ensure that the final design meets all engineering/customer requirements.
  2. Update cartridge design.
  3. Construct new POC out of aluminum tubing.
  4. Conduct testing on POC and analyze data.
  5. Keep track of items in BOM and budget.
  6. Research sensors (linear potentiometer and pressure transducer) and their outputs
  7. Research how to interact with sensors to record data and plot it
  8. Update MATLAB to have all functions required by customer
  9. Finalize CAD and develop detailed drawings
  10. Produce ANSYS on stressed structures
  11. Consult with client regarding design direction
  12. Call vendors about hydraulic cylinders to determine our best path.
  13. Schedule plans for MSDII and determine critical path and slack in the schedule.

Progress Report

Here, we summarize our accomplishments and other important topics as we complete Phase 4, our detailed design.

What the team plans to accomplish in this Detailed Design Review

Tasks have been accomplished so far

This section summarizes our major accomplishments broken out by functional areas.

Design

Test

Schedule

BOM

Tasks remain, and who is the owner of each

List of Tasks

Decisions that have been made so far These key decisions have been made regarding the design:

Team Progress Reports for Phase 4

Throughout Phase 3 and 4, our team kept detailed weekly minutes of our meeting and accomplishments. We have included a PDF of all Phase 4 weekly meeting minutes. WeeklyMinutesPhase4

Prototyping, Engineering Analysis, Simulation

During the previous design phase, we created a prototype to test our spring concept and discover and potential problems in our design concept. The prototype contained two concentric springs in a PVC pipe with 3D printed backstops. A piston was placed inside another PVC pipe. The plan was to pressurize the piston housing with a bike pump, forcing the piston into contact with the springs. We would measure the pressure and the spring displacement to recreate the pressure vs. displacement graph Meggitt requires.

POC Full Assembly

POC Full Assembly

Before testing, we learned from Prof. Wellin that PVC pipe is not rated for compressed air and could potentially shatter. We therefore abandoned this test method in the interest of safety. Our initial thought was to replace the PVC piston housing with an aluminum pipe. We discussed this with Dr. Gomes to double check that the aluminum would be safe to pressurize. During our meeting, he gave us the idea of testing the springs with various masses, letting gravity apply the force. For our second test, we placed the spring housing vertically and hung a “basket” from the bottom to contain the weights. The basket was attached to a rod which went through the springs. At the top of the rod was the piston head, which would compress the springs as the masses pulled on it.

POC Test #2

POC Test #2

We measured each mass added to the system and calculated the force due to gravity that was acting upon the springs. We also marked the rod for each added mass to show the displacement, and measured it with a caliper. This gave us a force vs. displacement graph. Force is proportional to pressure, so this graph is analogous to what Meggitt wants.

POC Graph

POC Graph

The data did not give us the expected curve. We calculated a turning point at around 33 lbs of extra weight, which is where we get the flat slope in the middle. The first and third slope are also not distinct enough to be the slopes we wanted. Our initial guess was that this could be corrected manually. When attempting to code the setup in MATLAB, it was found that there is a transition slope between the two main slopes unless the second slope is given a y-intercept to connect it to the first slope. If this was the case, we would get the following graph. There are two distinct slopes, though the ratio between them is smaller than desired.

POC Matlab Graph

POC Matlab Graph

After conversing with Kyle about our results, he suggested that we may have simply missed the first curve during our test. We revisited our calculations and discovered he was right: the turning point was actually around 7 lbs, and our basket was over 8 lbs. By adding the basket to the assembly, we skipped the first curve entirely. We tested the prototype for a third time to get more data. This time we factored in the lessons we learned from the previous test: add masses at linear increments, and be more precise when measuring displacements. Instead of adding a heavy basket, we hung the masses from the end of the rod.

POC Test #3

POC Test #3

We added masses in 1 lb increments until we were past the turning point, and then added a few 2 lb masses for extra data points. Our graph clearly shows the two slopes.

POC Test 3 Data

POC Test 3 Data

Adding in the data points from the second test gives us the desired and expected graph, showing that our proof of concept is correct.

POC Tests Combined

POC Tests Combined

CAD / Designs

Spring Disc Calculations

Designs were developed on expected spring disc stack heights and the dimensions of the spring discs used.

Step 1: Using Meggitt's previous test data for six different brake programs, ranging from Very Small Jet to Large Commercial Jet, hydraulic displacement data and pressure were converted into desired linear displacement and force respectively. From this desired spring rates for each section of the curve were found. A MATLAB script shown here SpringCalculations.m is used to convert the data. Using nominal pressure values of 300O PSI, and a bore diameter of 3.25 in. data is ported to step 2.

Step 2: An excel spreadsheet NewerSchnorrSpringDiscCalculator.xlsx uses the MATLAB data as an input and determines the necessary parallel and series stacks of a certain kind of spring disc to achieve the desired spring rate and displacement with +/- 5%. Using the spring force equation for a single spring disc as shown, basic Hooke's laws are applied to determine the necessary spring disc values. Discs stacked in parallel multiply load, while discs stacked in series multiply possibly displacement.

Force of a Single Spring Disc

Force of a Single Spring Disc

Step 3: The entire Schnorr Spring Disc Catalog is searched by the excel spreadsheet to determine the optimal type of disc and stack configuration capable of achieving the desired displacement, force and spring rate for a given brake program. Design parameters for selecting the spring disc are linearity, tolerance from desired loading, tolerance from desired spring rate, and number of spring discs per stack. What results is the table of spring discs below.

Force of a Single Spring Disc

Force of a Single Spring Disc

Cartridge Design

The piston will push the cylinder holding the larger spring discs as one unit, as the active spring discs will the ones with the smaller k value. Once the cylinder assembly reaches the stop off, then the larger spring discs will become active. The base will then be subjected to the largest portion of the applied force. Stress analysis can be performed to verify that the base will withstand the force.

Cartridge System Exploded View

Cartridge System Exploded View

Final Design: Spring Pack Configuration

The second design is functionally and conceptually equivalent to the original design, but with the addition of a preload that is applied to the springs to ensure that there are smooth transitions between k values in the pressure vs. displacement curves that will be output, and to increase the working life of the spring discs. The base in this design is more robust than in the original, and incorporates a bolting pattern that allows the base to be fastened securely to the steel plate and the cart in order to better withstand the applied force.

As shown, Pack A (smaller cylinder) and Pack B (larger cylinder) provide the small and large curves necessary to replicate a brake's behavior. These packs can be customized to any spring rate desired using the analysis method as shown earlier.

Pack A uses a center rod and nylon shims to keep the spring discs in place. Pack B uses a cylindrical nylon shim to center its spring discs. Both the centering rod of Pack A, the centering shims of Pack A and the centering nylon cylinder of Pack B must be machined to match the ID and OD respectively of the spring discs used. As such for each program a new set of these shims must be produced. Additionally, the Pack B head must be machined to match the ID of the Pack B cylindrical shim for each new program. As such, these four (Pack A rod and base, Pack B head and nylon shim) components are the only ones that will need to be swapped when adding programs. As per the team's detailed design review on May 4th, 2018 we will be moving forward with the spring packs final design for the AABS system.

Pack System Isometric

Pack System Isometric

Pack System Exploded View

Pack System Exploded View

Pack System Drawing

Pack System Drawing

Manufacturing Prints for Final Design

The prints as shown will be used in MSD II to fabricate the spring pack system for use in conjunction with the piston to provide displacement data.

Sturcture

Strucutral Block

Strucutral Block

Hydraulic Cylinder and Cartridge Base

Hydraulic Cylinder and Cartridge Base

Cartridge Cover

Cartridge Cover

Cartridge Container

Cartridge Container

Pack A

Pack A Head

Pack A Head

Pack A Base Plate

Pack A Base Plate

Pack A Spring Disc Assembly Centering Rod

Pack A Spring Disc Assembly Centering Rod

Pack A Centering Shim

Pack A Centering Shim

Pack B

Pack B Head and Force Plate

Pack B Head and Force Plate

Pack B Base

Pack B Base

Pack B Spring Disc Assembly Cylindrical Centering Shim

Pack B Spring Disc Assembly Cylindrical Centering Shim

Pack B Pressure Plate

Pack B Pressure Plate

Complete System

The final design incorporates a hydraulic cylinder, the spring pack loading system, as well as bleed air system, micrometer valve, check valve, fluid restrictor and red oil reservoir. In additional a magnetic position sensor and fluid pressure transducer will be used to measured the systems output linear displacement and on-board pressure respectively, as shown in purple. A hand-pump provides fluid pressurization and a reservoir supplies the fluid. These two items are not included on the cart.
Pack Design Complete System

Pack Design Complete System

Bill of Material (BOM)

For this phase, two BOMs were made in order to compare the total number of components, sub-assemblies, and cost of the cartridge and spring pack designs. The BOMs include a level of assembly, manufacturing number (if applicable), description, whether it is bought or made, and which sub-assembly each component fits into. The spring pack design was found to be more cost-effective, easier to manufacture, but included more purchased items.

Pack System BOM

Pack System BOM

Cartridge System BOM

Cartridge System BOM

Preliminary Test Plans

Setup

  1. Zero pressure transducer
  2. Zero linear potentiometer
  3. Verify that graduated cylinder is empty
  4. Fill system with hydraulic fluid.
    • Let some fluid out of the tap so that air is fully bled.

Simulation

  1. Choose program corresponding to jet size
  2. Place program [cartridge/spring packs] in fixture
    • Adjust distance of stop-offs as required
  3. Slowly pressurize fluid until maximum program pressure is reached
  4. Record pressure and displacement
  5. Loosen micrometer valve to release a small increment of hydraulic fluid into the reservoir
  6. Record volumetric/linear displacement
    • Volumetric will be subtracted from the initial volume
  7. Repeat steps 5 and 6 until pressure has returned to zero
  8. Plot pressure-displacement points
  9. Compare resulting plot to brake tests if available

ER Compliance

Risk Assessment

We added three new risks for this phase. The first two deal with time management for the end of the semester. We need to get the design finished and the components ordered by the end of MSD I so that we can start building and testing immediately in MSD II. The big problem is the spring disk calculations, but now that those are solved, we are able to move forward with the rest of the tasks we need to complete. The third risk is that the spring disk calculator gives a stack of spring disks for the specific slope we input, but the output is not exactly what we wanted. There is a tolerance of about 5% between the desired and expected slope. We will work to close that gap, and also inform Meggitt.

New Risks

New Risks

We updated all risks involving the prototype to a likelihood of 0. Two of them involved the prototype, and we found a testing method that excludes that. The third was that we would not get an accurate pressure vs displacement curve and we would have to rethink our design, but we collected our data and found that we got exactly what we expected.

We also set the risk of being unable to find good springs to 0, as we switched to spring disks to avoid this problem. Switching to spring disks allows us to lower the likelihood of the simulator being too large as well, as the spring disks have smaller displacements.

Finally, we were able to lower the likelihood of hydraulic leakage from 6 to 1, as we are going to buy a hydraulic cylinder instead of manufacturing one ourselves. This was our most important risk, with an importance of 54, but it is now done to an importance of 9.

Updated Risk Assessment 1

Updated Risk Assessment 1

Updated Risk Assessment 2

Updated Risk Assessment 2

Design Review Materials

Detailed Design Review PowerPoint

Plans for next phase

MSDII Plans

MSDII Plans


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