Our documents can be found in the Systems Level Design Documents directory.
Team Vision for System-Level Design PhaseFrom our standing after the Problem Definition Review, we were able to move forward and create a functional decomposition for our entire system. After reviewing current products, our competition, we managed to brainstorm our own ideas as to how some of these particular functions could be completed. We then created criteria by which to compare our new ideas and rated them appropriately. Once we produced the best design for functionality, we analyzed the feasibility of the design. With our design in place, we aim to make progress and keep driving towards our final goal.
Above is the functional decomposition for our project. The parts outlined in red went under further scrutiny as to how we wanted to accomplish these functions.
There are three main functions to an ADCS test is to obtain the CubeSat and customer requests, setup the apparatus accordingly, and to finally run the test and record the results.
The category with the most variability is the apparatus test setup. Within this category, functions such as collapsibilty, test bed, calibration, and test execution. The functions listed are further explored in the morphological chart.
Some three axis versions are available but are mostly custom ordered. A refurbished Helmholtz coil cage was found as seen below, with a retail price of $21,900, and refurbished price of $1,950.
This Helmholtz coil cage uses 3 Watts of power max and creates up to a 1 Gauss magnetic field. The dimensions of the Helmholtz coil cage is 82cm x 72cm x 64cm.
Morphological Chart and Concept Selection
Most Viable Options from Morphological Chart
- Swivel Design
- Test Bed
- Low Friction Sphere
- Power Supply
- Test Execution
- MATLAB Interface (CSV)
Combinations Moving Forward in the Selection ProcessFrom the Ideas presented above, all possible fusions of ideas are as follows:
- Swivel Design, Low Friction Sphere, Power Supply, MATLAB (CSV)
- Swivel Design, Suspension, Power Supply, MATLAB (CSV)
- Swivel Design, Counterbalance, Power Supply, MATLAB (CSV)
- Disassemble Coils, Low Friction Sphere, Power Supply, MATLAB (CSV)
- Disassemble Coils, Suspension, Power Supply, MATLAB (CSV)
- Disassemble Coils, Counterbalance, Power Supply, MATLAB (CSV)
Concept SelectionCriteria used in the concept selection process:
- Collapsed Volume
- When our apparatus is not being used, and in storage, its final collapsed volume should be as small as possible.
- Safety of Design
- The apparatus should pose as little danger as possible to the user(s) involved and the environment in which it is subdued. The apparatus needs to exhibit these safety standards during phases such as assembly, test setup, test execution, disassembly, and storage.
- Time to Deploy/Deconstruct
- Device setup and tear down should not be significant time factors in regards to test planning.
- Time to Creation
- How long will this design take to research and initially construct?
- Feasibility (Construction)
- Are the skills, hardware, and manufacturing equipment readily available within our group and here at RIT.
- Will this project stay within the $500 budget we were given?
- Field Accuracy
- Will this apparatus design yield a field that could potentially exceed our accuracy demands, or not?
- Field Size
- Will this apparatus design produce a field that exceeds our dimensional (10cm x 10cm x 10cm) demands, or not?
- Construction Robustness
- Will the design be able to overcome alterations that come with natural wear an tear over time?
From the Pugh Chart above, we were able to determine the combination consisting of the disassembled structure, a low friction sphere, power supply calibration, and the MATLAB interface utilizing CSV files would be optimal.
Notes regarding the Pugh Chart:
- Assumption: The Low Friction Sphere could be 3D printed. We are still unsure if the Low Friction Sphere will have to be machined or not.
- Assumption: The Test Bed was of lower importance, when weighting.
- The Swivel Design is much harder to both design and construct
Feasibility AnalysisThe power requirements, magnetic field requirements, spatial requirements, and cost were analyzed for feasibility
- An Agilent E3631A triple output put supply is the standard power supply available in the R.I.T. computer engineering labs. This supply is used as the baseline for further analysis. This supply has two outputs of 25V, 1A max and one output of 6V, 5A (max). Keeping things equal, the highest available voltage on each output is 6V and highest available amperage is 1A. Thus, providing a power constraint baseline
- The number of coil wraps to produce a magnetic field in a circular Helmholtz coil can be determined from the equation below, which has been derived from the Biot-Savart law
Where B is the magnetic field, N is the number of wraps, I is the Amperage, and R is the radius
- A magnetic field of +/-2G was used for the magnetic field (+/-1G Customer requirement). Amperage of 0.5A was used, as our power constraints are limiting to 1A, and there are two coils per output. And a Radius of 34cm was used as it is the largest coil pairing and has the most constraints
- The result of this equation produces an N value of 153 turns (323.3m or 1060ft of wire per coil)
- Finding the correct wire gauge can be completed using Ohms law (R=V/I) where R is resistance, V is voltage, and I is amperage
- The necessary resistance is 6V/0.5A or 12 Ohms for the entire length of the wire
- With a wire gauge of 20 AWG, there is a resistance of 10.15 Ohms per 1000ft (meets calculated requirement)
- Our estimate of 26cm x 30cm x 34cm for a uniform field volume would be sufficient enough to handle a 10cmx10cmx10cm CubeSat, with room to spare for a stand
- Regarding power, purchasing a new power supply would
easily go far above our $500 limit. Seeking out
programmable power supplies on campus is a big constraint
that addresses many feasibility factors
- Using a power supply from RIT, described above, would eliminate the cost
- Continuing with cost and power constraints in mind, the length of the wire and the wire gauge play an important role
- As calculated above, a coil requires 153 turns, or 1060ft of wire per coil
- Using the max of 1060ft per coil, for 6 coils, gives 6360ft of wire in total
- One 10lb spool of 20AWG magnet wire provides around
3200ft of wire and costs between $100 and $130
- Two spools totaling $200 to $260 will meet our length requirement
This is well enough below our financial limits to be considered feasible, as well as hits our power limitations, spatial limitation, and magnetic field requirements
This is a rough draft of what our bill of materials will look like.
Designs and Flowcharts
This is the ideal process when performing a calibration on the apparatus.
This is the ideal process for producing the magnetic field in order to execute a ADCS test with the apparatus.
Risk AssessmentThis is the updated Risks Chart, from the Problem Definition Review, along with the proper Risk Analysis
Plans for next phase
Team GoalsWe hope to have a well developed BOM, completed the feasibility and risk analyses of the subsystems, and adequate schematics for the respective subsystems. In addition, we hope to produce a small prototype as a proof of concept to verify our calculations.
- Finalize a brand and type of wire that will meet both our performance demands and budget
- Helmholtz Coil Simulation (Finite Element Method Magnetics)
- Analyze materials researched and analyze the cost differentials
- Produce schematics for apparatus (both deployed and collapsed)
- Research heat output and heat tolerance