Table of Contents
Team Vision for Detailed Design Phase
By the end of MSD I the team hoped to:
- Finalize new chamber design concepts
- Select Diaphragm to move forward with build & test
- Begin initial testing, finalize test plans
- Close any open issues with full system design
To see all any and all documents associated with this cycle, see the Detailed Design Documents repository.
Prototyping, Engineering Analysis, Simulation
Initially, two inexpensive different types of air brake diaphragms were purchased to test for characteristics and design feasibility. Unfortunately, the diaphragms purchased were too large and rigid for the current design's use, as they are used in large industrial air brake applications. This was where the current design's inspiration came from (see PDD Critical Design Change).
Based off this knowledge, the team hoped to find a diaphragm better suited for the current design. This was based off of the following requirements:
- Outputs required stroke volume (derived from human physiology & Engineering Requirements)
- Withstands operational pressures
- Very minor resistance due to movement of diaphragm
- Easily compatible with spring piston design
After looking at multiple designs, it was the third point on this list that led the team to DiaCom's design for diaphragms, which are used in a wide array of industries. The diaphragms design (pictured below) uses edges that fold over on themselves to allow the diaphragm to "roll" as it moves up and down, which creates virtually no resistance to motion. The diaphragms are often fitted with springs or pistons, which fit well with the current design. Ultimately the team chose to use diaphragm F-475-187.
|DaiCom Diaphragm Schematic||Selected Type F Diaphragm|
Pressure Analysis Updates
Once the diaphragm design was selected, a final Hydraulic Analysis could be conducted to understand the relationship between pneumatic air pressure, and required hydraulic pressure increase. Using diaphragm geometry, a free body diagram, and the simple relationship that Pressure = Force divided by Area, a formula was created that can calculate pneumatic pressure as a function of:
- spring constant, k
- stroke volume, V
- diaphragm areas (Total, piston, and sides)
- required hydraulic pressure increase, P_h
To see a full analysis for how these equations were derived, see the Hydraulic Calculations PDF located on EDGE.
This equation was then integrated into the PDD hydraulic calculation spreadsheet, where previously derived values could be plugged into the equations to calculate pneumatic pressures under different circumstances. This spreadsheet was also helpful for experimenting with different k values of the spring, allowing one to observe the affect of a changing spring constant on required pneumatic air pressure.
|Chamber Schematic||Pneumatics tab screenshot|
Click here for a link to the live Hydraulic Calculations xlsx document.
CAD Model Updates
Major updates to the CAD model included:
- updating design to include chamber-long rods to keep end caps in a fixed position
- flattening sides of caps to be used for stability so device doesn't roll
- diaphragm design with piston & plate included
- bulkhead fittings changed to uniseal
Screen shots of CAD:
|New chamber - full view||Exploded view of Chamber|
Drawings, Schematics, & Flow Charts
LabView Flow Charts & Transfer FunctionsThe data aquisition flow chart was updated since last cycle, created the following:
Transfer functions & algebraic relationships for the system were also derived during this cycle, specifically for pressure and flow rate, respectively. Below are the following formulas:
- Q = flowrate
- N = # of signals
- t = time
- V = volume per signal
|Hydraulic End Cap||Pneumatic End Cap|
To see assembly drawings for the current CAD model, see the "Drawings" folder
Bill of Material (BOM)
Several parts were updated from our last cycle, as major design parameters were finalized, allowing final selection for almost every item listed on the final BOM:
See a link to the live Excel document here
Test plans were updated and refined during the DDR cycle. Several detailed test plans were also created. The entire list of test plans was tabulated into a spreadsheet:
See the live Excel Document here
Detailed Test Plans
Detailed test plans to be completed:
- Pressure Regulator
- Three Way Valve
- OneWay Valve
Detailed Test Plans (Results)
See a link to the more in depth, live Excel document here
Some notable mitigation plans that were put in place this cycle:
- introduced fuse to design, over current protection
- spring design to provide linear function
- corrosion resistant coatings to be placed on materials in contact with water.
Design Review Materials
Too see the PDF of this cycles design review presentation, Please click here.
See a link to the live excel documentHERE