Preliminary Detailed Design
All the documents for this phase are in the Detailed Design Documents directory.
Team Vision for Preliminary Detailed Design PhaseReviewing the work done in the Subsystem Phase, we were able to better realize items that needed to be done in order to have a successful Preliminary Detailed Design Review. As a team, we needed to develop a draft of a test plan and also a propose a schedule for MSDII. From the mechanical perspective, CAD modeling and developing a method for manufacturing were of utmost priority. From the electrical side, creating a real size prototype and magnetometer calibration.
During this phase we were able to accomplish many of our goals, such as CAD modeling, a plan for manufacturing, prototype creation, and magnetometer calibration.
An image of the prototype of the smallest sized coil with 54 wrappings. While constructing this prototype, we learned we may need a deeper groove in the coil. This edit was translated into our CAD modeling. We also initially had some concerns about working with the 20AWG wire, thinking it may be hard to work with, but these concerns were alleviated when coiling the wire.
Jakob holding the smallest coil prototype for scale.
The setup of the smallest prototype when taking measurements. There are a few main components to be seen in this image. The coil, power supply, arduino, magnetometer, and laptop.
Drawings, Schematics, Flow Charts, Simulations
A 3D model was created using SolidWorks.
This is our rendition of a collapsible, 3 axes Helmholtz Coil cage that is drawn to the mathematically derived dimensions. For further viewing, the .stl and PDF versions can be found below:
The .stl can be viewed (after being downloaded) at: http://www.viewstl.com/
The magnetometer was calibrated with the help of a program called MagMaster. The program and a tutorial for using it can be found here. For calibration, the magnetometer was held in several different orientations and the values were recorded. Then a matrix and a bias vector were produced, which is used on the raw data to produce the calibrated output. The results of the calibration were very successful and can be seen below.
Preview of the uncalibrated magnetometer values. The full video can be seen here.
Preview of the calibrated magnetometer values. The full video can be seen here.
On the left is an image of the magnetometer outputs. On the right is the earths magnetic field in Rochester. It can be seen that the magnitudes of the measured magnetometer values are very close to actual values. Environmental effects such as nearby metallic objects could be the cause of the discrepancy.
This is the setup used when calibrating the magnetometer. The magnetometer was oriented using a box. It connected to the arduino using an I2C interface, which connected to the computer over usb. The values shown in the video are the expected values for the magnetic field in Rochester.
- Cut our coil rings from plywood (more details below)
- Using the wood glue, apply adhesive to the corresponding pieces
- Once the glue has been cured, apply spar urethane to each coil
- Once the spar urethane has dried, wire will be wrapped around the coil
After consulting the Construct @ RIT (http://hack.rit.edu/) we learned:
- The CNC router can only handle 5' x 5' (plywood is sold 4' x 8')
- We need to acquire our own bit: carbide, 1/8" diameter, 2 flute, 1/2" length
- Brief demo of VCarve (cutting software) that will be used to operate CNC router
Plan for Cutting(all measurements are in cm)
This is a picture of how we plan to approach the cutting of our coil constituents (rings). As shown on the left, the outer rings can be cut three at a time, thus the sheet of plywood will have to be split into thirds initially, before being placed on the CNC machine. Likewise, the inner rings will be cut out in a similar manner (shown on the right). The outer ring will be cut out of a sheet of .25" thick plywood, while the inner rings will be cut out of .5" thick plywood. Note there will be excess plywood, assuming all things go as planned.
This is an image of what we expect to see produced from our cuts.
Ready to Cut
- We have completed the VCarve files
- We have files ready for the CNC router
- We plan to 3D print our connecting pieces at the Construct @ RIT
- For the pieces that are too big, we are looking into using the Brinkmann Laboratory here at RIT to 3D print them
- Also Stratasys Direct Manufacturing (https://www.stratasysdirect.com/) could be an alternative for 3D printing
Coil Circuitry Block Diagram
This is a block schematic diagram for the proposed coil. The computer communicates with both the power supply and the arduino. The arduino is used to read measurements from the magnetometer as well as control the relays for the polarity switching. Polarity switching allows the coils to get the full -0.5A to +0.5A instead of just 0.0A to +0.5A.
Further Finite Element Method Magnetics (FEMM) analysis
This is an image analyzing the effects of the coils being 2cm further apart than it is supposed to be. The largest coil was used because it has the least tolerance in terms of power.
This is an image analyzing the effects of one of the coils being 2cm wider than it is supposed to be. The largest coil was used as it has the least tolerance in terms of power.
Bill of Material (BOM)
This is the most recent bill of materials. Please note this is an overestimate on some materials, such as plywood.
Test PlansAll of the following tests need to be done indoors, and be in a pressure, temperature, and humidity regulated area. Additionally, the constituents of the local environment need to be non- ferromagnetic. Please consult someone who is experienced with magnetic fields before setting up the apparatus at any location.
The engineering requirement met by each test is highlighted in light blue. The name of each test is in bold.
Final Collapsed Volume Test
- Purpose: As it was asked of us to design a Helmholtz cage that is able to be taken apart for storage, we need to ensure the method and end result of disassembly satisfy this design requirement.
- Plan of Execution:
4 people, 3 trials each, Helmholtz cage should be setup prior to test (without magnetometer implemented), all electrical components should be unplugged
1. Individual(s) is/are to follow the presented disassembly directions
2. Once disassembled, the individual(s) must place the pieces in the specified layout for storage
3. Once the pieces are in the final positions, the individuals must verify their piece placement and acknowledge the approximate collapsed volume
- Purpose: This test is intended to ensure the safety of the design in regards to the magnetic fields produced and any other by-products of operation.
- Plan of Execution:
4 people, 3 trials each, Helmholtz cage should be setup prior to test (without magnetometer implemented), all electrical components should be plugged in
1. Turn Power Supply on
2. Let apparatus run for 15 minutes
3. Take magnetometer and walk 2ft around the apparatus whilst operating
4. Record the magnetic field readings
5. Compare these readings to that of relevant standards
6. Determine if these measurements abide the standards
7. Take note of any other byproduct, emissive, etc
8. Determine if these are of concern
Time for Setup, Magnetic Field Precision
Assembly Speed and Accuracy Test
- Purpose: Creating a mechanism that is not too complex for future users was of utmost importance to us. Not to be overlooked is the repeatability of an accurate setup.
- Plan of Execution:
4 people, 3 trials each, Helmholtz cage should be in disassembled/storage state prior to test, all electrical components should be unplugged, individual performing test should have viewed the support documentation as to the assembly of the apparatus
1. Have a timer at hand to record the time it takes to assemble the cage
2. Begin building the structure after starting the timer
3. When structure is assembled, stop the timer and record the elapsed time
4. Connect all of the electrical components
5. Power on the apparatus and set the settings to produce a 0 +/-2 Gauss Field
6. Taking readings from the magnetometer to validate the setup
ADCS Cage Duration Test aka “Set It and Forget It”
- Purpose: ADCS tests can run for extended periods of time. As designers of this apparatus, we need to make the final product is capable of running for long durations without failing (overheating, mechanical stress, etc.).
- Plan of Execution:
1 person, 1 trial, Helmholtz cage should be setup prior to test (with magnetometer implemented), all electrical components should be unplugged
1. The individual must connect all of the electrical components accordingly
2. Be sure the magnetic field in the cage is 0+/- 2 Gauss from the magnetometer
3. Let the apparatus run for 4 hours
4. Check the magnetometer readings (make sure it is corresponding to what it initially was)
5. Turn off the power source
6. Check the structure for any failures (electrical or mechanical)
This is the updated Risks Chart, along with the proper Risk Analysis
In regards to engineering standards, we have reached out to the NTID and we are awaiting a response detailing any performance requirements for hearing aids.
Plans for next phase
- Create a real coil
- Further develop test plan
- Develop plan for MSDII
- Finalize structural design
- Finalize manufacturing process
- Have all materials ordered
- Order Wire
- Record valuable prototype data
- Design relay circuit