Preliminary Detailed Design

Table of Contents

All the documents for this phase are in the Detailed Design Documents directory.

Team Vision for Preliminary Detailed Design Phase

Reviewing 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

CAD Modeling

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/

Magnetometer Calibration

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.



After consulting the Construct @ RIT (http://hack.rit.edu/) we learned:


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.

Expected Yields


This is an image of what we expect to see produced from our cuts.

Ready to Cut


Other Pieces

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 Plans

All 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.

Collapsed Dimensions

Final Collapsed Volume Test

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

Environmental Inspection

Environmental Evaluation

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

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”

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)

Risk Assessment

This is the updated Risks Chart, along with the proper Risk Analysis


We were able to find some metrics on pace makers which reported 5-10 Gauss as the maximum before a harmful impact may be caused. This is not an issue as our apparatus can only produce +-2 Gauss. Sources can be viewed below:

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

Team Goals

Individual Goals



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