P16105: RIT-SPEX ADCS
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Subsystem Design

Table of Contents

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

Team Vision for Subsystem-Level Design Phase

In this phase we divided our device into subsystems with the intent of further developing each of the individual systems. Our plan of action was to design and begin determining which materials we would need for these respective subsystems. Both feasibilities for each subsystem and an overall BOM will be created. Supporting materials such as schematics, proof of concepts, and risk assessments will also be documented.

By the end of this phase, we were able to develop schematics utilizing FEMM to simulate the magnetic fields we have derived. Also, we have further developed our design for collapsibility amongst our other subsystems. Through all of this, our Bill of Materials (BOM) achieved a greater level of completion. Lastly, a Gantt chart was completed for the remainder of this semester.

Feasibility: Prototyping, Analysis, Simulation

Magnetometer

The first magnetometer we decided to use was the SparkFun Triple Axis Magnetometer Breakout - HMC5883L. This magnetometer is widely available as it is very popular among hobbyists, and also very cheap, which was perfect for our evaluation needs. After becoming more familiar with this magnetometer we will determine if it is sufficient for use in our finished product, or only effective for our prototyping.

To interface with the magnetometer we decided to go with the Arduino Uno. This an extremely popular beginner microcontroller. It was chosen over the Texas Instrument MSP430 series mainly because of Matlab integration. It is much simpler to connect and integrate an Arduino using Matlab than it is an MSP430. For this reason, we decided it would behoove our customers to use the Arduino.

The Arduino to magnetometer interface is shown below along with the source code for rapid testing provided by SparkFun.

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Arduino schematic

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Block diagram schematic

SparkFun source code

SparkFun Tutorial

Coils

Pugh Chart (Coil Structure)

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From this Pugh Chart, we determined the 'Spool' design was best because of its lowered difficulty of construction, in comparison to the 'Grooved Ring'.

Finite Element Method Magnetics (FEMM) Analysis

Utilizing the FEMM software, we were able to create simulations that reinforce our calculations done in prior design phases. The visual depictions produced allow us to realize how the magnetic field varies in strength over the respective plane, as the point of interest strays from the origin. Each of the coils was given 0.5A and both the power and resistance requirements coincide with values we determined in the prior design phase. For this modeling, each coil used 154 wrappings of 20AWG.

Coil: 26cm Radius

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26cm coil

The green "CubeSat area" displays the area taken up by the 10cm by 10cm CubeSat. The blue "Maximum CubeSat area" is the maximum area the CubeSat can take up if it was oriented so the longest cross section was on the plane. This is the cross section from one corner to the opposite corner of the CubeSat, with respect to three axes.

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26cm single coil simulated power

Coil: 30cm Radius

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30cm coil

The green "CubeSat area" displays the area taken up by the 10cm by 10cm CubeSat. The blue "Maximum CubeSat area" is the maximum area the CubeSat can take up if it was oriented so the longest cross section was on the plane. This is the cross section from one corner to the opposite corner of the CubeSat, with respect to three axes.

public/FEMM\30_power.jpg

30cm single coil simulated power

Coil: 34cm Radius

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34cm coil

The green "CubeSat area" displays the area taken up by the 10cm by 10cm CubeSat. The blue "Maximum CubeSat area" is the maximum area the CubeSat can take up if it was oriented so the longest cross section was on the plane. This is the cross section from one corner to the opposite corner of the CubeSat, with respect to three axes.

public/FEMM\34_power.jpg

34cm single coil simulated power

Single Coil Prototype

public/Subsystem%20Design%20Documents\Pictures\prototype.jpg

This is an image of the prototype that was created. It is a single coil with a radius of 11.5 cm and 80 coil wrappings. It was tested with the magnetometer and a power supply. Changes in magnetic field strength were measured as a differentiating coil amperage was applied. The coil will be characterized further as more data is collected and analysis is performed.

Software

The software subsystem will become more significant as time goes on by for now the main focus is on the desired functionality and method of implementation. As a customer requirement we were tasked with running the software in MatLab. The software will have to interface with the magnetometer (through the Arduino) as well as the power supply. The different software functions can be broken down into layers, with each function requiring and utilizing the function before it.

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Software functionality stack

Structure

Pugh Chart (Wood Selection)

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Pugh Chart (Construction Materials)

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From the Wood Selection and Construction Material Pugh Charts, the '.25"x4'x8' Sande Plywood' is shown to be the best option. For the chart above, the asterisk indicates far Worse than DATUM

Pugh Chart (Collapsibility)

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As shown in the Collapsibility Pugh Chart, the 'Two Piece, Interlocking' mechanism yielded as the most viable option.

The intended means of implementing the 'Two Piece, Interlocking' mechanism was to adhere them to the wooden coils. Research was done on various wood glues to see which would be the best option.

Pugh Chart (Wood Glue)

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From this Pugh Chart, the Elmer's Wood Glue turned out to be the best option. We determined the price difference and the fact Gorilla Glue expands as it dries are why Elmer's came out as the front runner.

Bill of Materials (BOM)

This is the updated Bill of Materials from the materials we have selected.

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Bill of Materials Document

Risk Assessment

This is the updated Risks Chart, from the Problem Definition Review, along with the proper Risk Analysis public/Subsystem%20Design%20Documents\Pictures\risk_chart.jpg

Risk Chart Document.

Plans for next phase

GANTT Chart

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Gantt Chart Document.


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