Subsystem Build & Test
Table of Contents
Team Vision for Subsystem Level Build & Test Phase
- We tested the deployment
- We designed a new "spool" design for the deployment system
- We tested the nichrome wire
- We ordered our pcb main motherboard
- All electrical subsystems built
- OTS electrical parts obtained
- All mechanical subsystems designed
- Wormgear deployment mechanism machined
- PV deployment mechanism hinges machined
FabricationWe have been machining the cubesat for the past several weeks. The sheet metal was cut on the waterjet. The other parts were manufatured using the lathe and end mill.
The worm gear assembly was fabricated first. We bought all the gears, pinion and worm, but the mounting systems had to be made.
The bottom of the cubesat has a complex hinge arrangement. This hinge arrange will deploy the solar panels.
Below is the most recent version of the deployment system.
Test Results Summary
Initial Deployment TestDuring our first trial of deployment using just the full sized booms we found some problems. The booms initially started unwinding but then they expanded and got stuck inside of the cubesat. The motor then started winding the booms back up in the opposite direction. This can be seen in the picture below.
BalloonsWe planned to use balloons to keep the booms from falling while testing the deployment to simulate the lack of gravity but after testing a balloon and weighing the tape measures. We calculated that you would need two balloons per foot of tape measure. Since this would cause us to need almost 100 balloons we had to change our method of boom stabilization.
Deployment with Shorter BoomsWe tested our deployment with shorter booms. The 37 inches booms did not extend. We finally got the deployment working with the booms that last years team used. The picture of them unfurling can be seen in the picture below. These booms are about a 20 inches long. Since these booms are very short they are able to expand a lot and do not rub against each other as much which could be a reason these booms will actually expand. We want much longer booms in this cubesat in order to have bigger sails.
Using GuidesFor better deployment we tried adding guides into the deployment system that will help keep the tape measure rolled tight and help guide the tape measure out their intended exit. Our guides still caused the booms to jam. We also hot glued them in and the force would build up and the guides would break off at the hot glue. We would hold the guides in place after they would break but we still didn't notice much progress with the booms expanding.
Double Sided Tape TestWe next tested the booms using double sided tape. We wanted to know if it would have an easier time expanding if the booms were held together at the center. So double sided tape was applied between the booms starting about a foot from the ends of the tape measure that would exit the cubesat. The booms started extending from the cubesat better than any previous efforts. There was a problem once the tape got out to the opening though. One piece got stuck to the cubesat and started causing the booms to bind backward. We are going to look into a center piece which will hold the tape measure together and not involve tape.
Metal Plate Addition
After the tape test we decided to use a metal plate to try and keep the tape measure roll contained. We attached a rough machined "circular" plate to the top of our spool which will spin with the cup.
The plate did helped the tape measure unroll. We hadn't been able to get the half boom deployed at all before and using this method we were able to deploy it all the way.
Since this worked we have designed a new spidle that will have a plate on the top and the bottom, similar to a spool of thread. It was tested with the half size booms successfully. Going forward we will test with the full size booms and eventually with the sails attached.
To insure the nichrome wire will cut our fishing line we ran some tests.Various strands of nichrome wire were used to cut the fishing line using 12 volts from a power supply. 1 nichrome wire by its self did not cut our fishing line right away. It melted the fishing line a bit but we want the fishing line cute fairly quickly. Using two strands of nichrome wire the fishing line cut when pressing the nichrome and the fishing line together which can be seen here.
We will not be able to press the two together in space. We will pull them taunt against each other so there will only be a small amount of force. To test this we made a loop of fishing lines with the nichrome holding it up. Using just gravity the 2 strands of nichrome did not cut the fishing line. Three strands of nichrome wire cut the fishing line when only gravity held the two lines together. The fishing line will also be in an "X" fomartation holing the top of the cubesat closed so we tested if the 3 strands of nichrome would cut two strands of fishing line. This test can be seen here.
Our overall test results for the nichrome wire can be seen below.
Prototype and TestUsing prototype boards purchased last semester, a prototype of the power system was assembled and tested on a breadboard. This included the power multiplexer, battery charging, and the 5V and 12V boost converters.
PCB DesignUsing the successful tests from the breadboard prototype, the schematic of the power system was finalized and a board was designed. This board incorporates the following features:
- msp430fr5969 microcontroller
- External clock source for microcontroller
- Power multiplexer
- 3.3V regulator
- 5V boost converter
- 12V boost converter
- Battery charger
With the schematic diagram complete, a board was laid out. This board was designed to be modular and follow a stackable architecture for subsequent daughter boards. The pin assignments of the standard are found below:
This stackable architecture will allow multiple daughter boards to each have access to any digital or analog pin of the microcontroller, as well as any of the three power sources.
The baseboard has been ordered from oshpark, as well as all components from digikey. The baseboard has the standard connections described above as well as:
- Battery Connection
- Incoming Solar Connection
- Programming Connection for the microcontroller
- Kill Switch Connections to allow all power to be killed
Interactive Systems Architecture
An effort was undertaken to create a comprehensive design architecture for the sake of quickly referencing any design element in the current project phase, and increasing the ease of analyzing the current design in future phases. Developed on the framework of the functional decomposition created in MSDI, the architecture shown in the captures below organizes each and every component of the cube sat systematically. As components are organized into larger subsystems, diagrams such as electrical schematics, CAD models, or even captures of the prototype are shown to further illustrate the modeled subsystem. The architecture was developed using MATLAB Simulink modelling platform, and is eventually going to be interactive, where the user is able to simulate in real time the effect of ambient temperatures and vibrations on mechanical components, the power flow between electrical subsystem, and all interfacing in between subsystems, all in order to obtain a transient representation on how the cube sat was designed to function. The captures below were taken from just a few levels in the system hierarchy.
The Simulink file is available here.
The Majority of the code has been targeted at supporting the future testing for the project. This primarily involves the GPIO, Clock, and ADC settings and basic functions. The code is being stored primarily on the GIT repository which is publicly accessible for download. As certain stages in development are reached, code revisions are going to be posted in the EDGE repository as checkpoint for the code base.
Risk and Problem Tracking
The Risk Management document has been update through out this semster. This semester due to the issues with deployment, not getting the solar sail to deploy is our highest risk. Our updated design should help reduce the risk. Other risks
- Not getting parts water jet when we need them
- Not being able to fold the sail small enough
Since we faced some problems with the deployment we updated the problem tracking document which can also be seen below.
ScheduleThe updated schedule for next phase is shown below, along with the projected schedule from the previous phase.
BudgetAs of 2/22/2019, the project still has $428.73. Click HERE to download the full spreadsheet detailing all purchases so far.
Plans for next phaseFor the next phase, in three weeks, we plan to have all the parts machined. The electronics will be assembled as well. This will allow for electrics and deployment testing.
- Sail deployment test
- Finish Machining
- Update Schedule
- System Arch./Design Doc.
- PV Array Alternative Selection Study
- Sail deployment test
- Continue to assist with machining
- Solder and test power/control board
- Develop wire harnessing for sensors, motors, and nichrome wire
- Sail deployment test
- Sail deployment test
- Update test plans
- Update Risks
- Update edge page
- Sail deployment test