Preliminary Detailed Design
Project RecapThe High Altitude Balloon Instrumentation Platform (HABIP) is a multi-functional system that allows users to collect and analyze data from near-space experiments. The device records internal data, and also telemeters data that has been gathered from an array of sensors to a ground communications center. The goal of this project is to create the aforementioned array in a configuration that is lightweight, cheap to manufacture, and highly reliable. The final product will undergo a mission lasting for several hours in harsh conditions, and will parachute back to Earth from an altitude of over 100,000 feet to be recovered and analyzed. This project seeks to improve upon the progress of two former MSD groups: P17104 and P17105, and is intended to be a design which can be further improved in the future.
Team Vision for Preliminary Detailed Design PhasePhase Summary:
- During this phase, the team built upon high level plans and began examining how new designs will fit into the systems built by previous teams
- In particular, the team focused on:
- Structures and thermal analysis
- Integration of a new microcontroller
- Communications and digital video transmission
- Reaction wheel algorithm analysis
- Plans were laid out to test the new systems
- Block diagrams were updated
- A high level bill of materials was put together
- Funding levels were confirmed
- A plan of action for the next phase was put together
Designs, Drawings, Schematics, Flow Charts
PurposeDefine the layout and design of the final product.
Updated Block Diagramclick here.
Main Board Redesign
- Removing motor controller with MSP430 and replacing that MSP430 with Teensy 3.6
- Removing microSD circuitry (Teensy 3.6 has one built-in)
- Removing large blocky IMU and 9V battery, replacing with SMT LSM9DS1
- Implementing additional protection circuitry
- Adding video multiplexing circuitry
Updated schematics can be found here.
Other Design Updates
- Setup of DTV system is under way
- Balloon plug design is still being considered
- Power systems are unlikely to change significantly apart from requirements to video, this system will not undergo significant updates until other subsystems are finalized
Feasibility: Prototyping, Analysis, Simulation
PurposeComplete initial testing, and gather both qualitative and quantitative data that will drive decision making for continued engineering design. Simulate conditions that the final product will experience in flight.
Preliminary Thermal Analysis
Reaction Wheel Algorithm Analysis
The algorithm for last year’s motor, as well as comments on the plan moving forward can be seen below:
- Z RPM = RPM * 0.07326/6
- This needs to be updated to compensate for new IMU.
- error = z gyroscope in rpm
- integral = integral + error
- This can remain the same
- control speed = (kp*error)+(ki*integral)
- kp was 120 and ki was -0.2. These values are going to need to be updated to compensate for both the new weight and the new IMU. The new IMU may return different values than the old one, and this will be compensated for here. This is task number 2 in the list above.
- TACCR1= (Desired-Min Input)(Max Output-Max Input ) / ((Max Input-Min Input) )+Min Output
- This can stay the same, but may need to multiply it by a constant. Because the clock speed is faster on the Teensy than it was on the MSP430, this may need to be increased by a constant in order to keep the maxon controller happy.
- TACCRO = 20000
- This will need to be increased by the same constant as above.
Issues with code:
- SD writing was not continuously done while motor was running. This was a limitation of the MSP430 and can be corrected using the Teensy 3.6.
- The SPI communication with the Host MSP430 was not effectively integrated and was therefore removed before the fight. This needs to be reintegrated correctly.
- The SD card writing needs to be done more efficiently, it is currently taking seconds in order to execute, these needs to be brought down.
- Temperature and pressure measurements were not integrated. They need to be added.
PurposeDemonstrate objectively the degree to which the Engineering Requirements are satisfied, and determine what updates must be made.
Thermal/Structural AnalysisThere is no physical testing thermal performance planned, as physical testing will not provide useful results and will take too much time. Testing would need to be done in a vacuum chamber with a high level of incident radiation. As of now, we do not have the resources or time required to create these conditions. Analysis can and will be completed with FEA instead, using ANSYS.
- Determine all sources of heat on platform
- Build model with all heat sources
- Simulate model at apogee (worst case)
- Simulate model in a dynamic, altitude-increasing environment
- Use results to determine necessary radiative elements and/or changes to HABIP layout
Information needed to complete simulation:
- Thermal Generation of (in order of expected heat
- Motor Controller
- Motor Battery
- SDR Battery
- Transceiver Batt
- Pi-HAT Batteries
- COMMS board
- DACQS Board
- Power reqts. of SDR
- Need to determine appropriate battery for SDR
Inertial Measurement Unit (LSM9DS1)Steps:
- Test that the microcontroller is receiving the IMU
- Determine from the data sheet what should be sent and verify that the Teensy is receiving that data correctly
- Verify the data sent from the IMU is allocated to the correct value. (Z-direction gyro data stored in teensy z-gyro variable)
- Test Microcontroller communication with the motor
- Set up the board with IMU, and motor
- See if the reaction wheel turns on and spins in
- Spin the IMU in a direction and make sure the motor spins in the correct direction to counteract this motion
- Log data on micro SD card
Reaction Wheel StabilizationSteps:
- Test actual reaction wheel stabilization
- Set up the final assembled HABIP
- Spin the HABIP in a direction
- Motor turns on
- Motor stabilizes the platform
- Within one minute a constant angular velocity less than 360 degrees per minute should be achieved
Digital Video TransmissionSteps:
- Transmit over coaxial to do preliminary test
- Acquire and configure antennae
- Position DTV transmitter in Ellingson at top floor
- Test wirelessly across campus to METEOR Lab to simulate altitude
Bill of Material (BOM)
PurposeConfirm that all components are accounted for in the final design.
Click here for the working document.
- Potentially not enough bandwidth to transmit/receive
- Dr. Patru is now requesting less data transmission, particularly to accommodate easier integration of complicated digital video system
- Difficulty securing funding
- Boeing now supplying funds
- $1500 is available to the team in total
- Meeting times are challenging to coordinate with
seven team members
- MSD II minor scheduling conflicts have been discussed and handled
- Poor fabrication of PCBs is possible
- Remains an issue, will be unclear until MSD II testing
- Using high quality suppliers is a must
- Excessive time needed to write to microSD for data
- Continues to be a consideration particularly with reaction wheel algorithm getting increased attention
- Off-shelf components may not work as expected at
altitudes of >100,000 feet
- Limited testing opportunities
- Difficulty analyzing code from past teams
- A more apparent risk as code is more heavily analyzed
- Contact with past team members is used to clarify
- General safety (shock/burn) is a continued risk
- Team is using safe lab practices
New Sources of Risk
- Rooftop antenna is not made operational
- Component failure causes heat transfer model to be inaccurate
- Common mode failure affects redundant subsystems
Plans for Next Phase
Click here for the working document.