P18371: Meggitt Brake Simulator
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Subsystem Build & Test

Table of Contents

In Phase 2, Team Spring Breaker ordered and received materials needed to start machining, while waiting for the hydraulic cylinder to come in. A MATLAB script was created to make it easier to find the spring discs needed for each plane with its associated curve. This phase content of our Edge page includes detailed information and outcomes of our journey through our Subsystem Build and Test phase (Phase 2). It also includes links to important documentation completed during this design phase.

Team Vision for Subsystem Level Build & Test Phase

Summarize:

MATLAB

We developed a MATLAB script that provides the optimal spring discs for a given pressure displacement curve. This will allow Meggitt engineers to easily add new planes to the simulator.

To use the script, the engineer will input the three points on the pressure vs displacement graph that they are trying to mimic. The script will then read in a catalog of spring disc values and calculate the top three fits for each section of the curve. Spring discs are chosen based on their linearity, their closeness to the desired curve, and the total number of discs.

The script creates graphs showing the desired curve and the calculated spring disc curves so that the engineers can visually verify the results. A total of four graphs are created: A graph showing the top spring disc pick, the second best option, the third best option, and a final graph showing all options combined.

Top Spring Disc Option Graph

Top Spring Disc Option Graph

Top Three Spring Disc Options Graph

Top Three Spring Disc Options Graph

The next step involves creating a second mode that allows the engineer to input spring disc combinations and see the resulting graph. This will be used for double checking the ordered discs. The code for this in written and is in the debugging phase.

The final step will be to make a user friendly interface to make the script easier for the engineers to use.

Machining

Machining Pack A was the main focus of this phase. As most of the McMaster Carr stock was received mid-phase manufacturing began later than anticipated. As such the smaller components mainly in Pack A along were machined. Pack A consists of a center rod with an external diameter toleranced to allow for a close fit between the smooth section of the rod and the in-series spring discs used to produce the stiffness as desired for the brake profile. ¼-20 UNC external threading is applied on the first ½ in of the rod at one end and 1 ¼ in roughly on the opposite side. An aluminum head to interface with Pack B is screwed onto the smaller thread while a washer and ¼-20 UNC retaining nut is used to hold the spring discs in place. Prior to installation into the aluminum retaining block of AABS, the Pack A assembly must be pre-loaded. This can be accomplished by any clamp (assuming even loading). The large jet Pack A assembly as shown below the assembly is comprised entirely of AL-6061 components. All parts are axisymmetric and thus were machined on a lathe. Manufacturing was performed as per the operations illustrated in green in the manufacturing plan.
Machining Schematic

Machining Schematic

Spring Pack A for the Large Jet

Spring Pack A for the Large Jet

As per the machining plan shown Phase 3 will involve the manufacture of steel and more complicated geometries, requiring additional team member involvement and planning. As always quality assurance will be an important consideration in machining the high load components; any deviation from spec may result in improper loading scenarios if not caught (i.e. spring discs are off-axis from piston loading line of action). The planned machining times for the rest of the Packs is shown below.

Machining Times

Machining Times

Risk and Problem Tracking

For this phase, we added two new risks. The first is the risk of ordering incorrect parts. This is caused by misreading labels and not double checking our work. We've completed most of our purchasing, but we'll be extra careful when making additional purchases.

The second risk is not documenting any changes we make to dimensions when machining parts. This is caused by getting too absorbed in the machining process and forgetting to jot down the changes. We'll make sure to stop between each step and write down any adjustments. This is important so that our simulator can be reproduced in the future.

New Risks

New Risks

We also removed three risks from our risk tracker. The first is the risk of the springs being too heavy. This was mostly a concern with regular springs, not with spring discs. Now that our spring discs have arrived, we are confident that weight will not be an issue.

The second risk is the lack of access to pressure-grade materials. We have ordered all our material and have run calculations to ensure that it will hold up to the stresses it will experience.

The last risk is getting our vendors on the approved vendor list. We have successfully dealt with this problem and ordered all our items from the non-approved vendors.

Updated Risks

Updated Risks

BOM

Current BOM

Current BOM

The BOM shown in the figure above displays the final list of items that need to be purchased or manufactured. Items highlighted in green are delivered/completed, items highlighted in blue are on order, and items highlighted in red are under review pending calculations, quotes, or specifications. Items that are not highlighted are assemblies that need to be built, and will be marked green when completed and tested. All parts should be purchased in the next 2 weeks barring any significant setbacks.

Design Review Materials

P2 Subsystem Prep PowerPoint

Next Phase Plans

Schedule
Schedule

Schedule


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