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ATEx - Atmospheric Teaching Experiment



Leadership

  • Team Leader: Anthony Wagner, ME, 2018, email
  • Electrical Leader: George Boyer, CPE, 2019, email
  • Mechanical Leader: Derrick Neilson, ISE, 2020, email
  • Treasurer: George Boyer, CPE, 2019, email
  • SEC Rep: Anthony Wagner, ME, 2018, email
Mentors
  • Advisor: Dr. Jonathan Black, AOE
  • AMP Lab Mentor: Will Gerhard, EE, 2016, email
Current Status
  • Active: Accepting new members
  • Currently designing and constructing bus structure and payload in anticipation of an April 2018 launch date
    • This launch will be a payload that will circumnavigate the earth

Project Overview

ATEx is a design and educational outreach program that uses high altitude weather balloons to teach K-12 students about science and engineering. The Design Team 

designs and builds the balloon payloads while mentoring members through the engineering design process and teaching them hands-on skills. The Outreach Team uses this design process, launch, and collected data to create and implement elementary, middle, and high school curricula. ATEx aims to excite, engage, and teach both K-12 students and its own team members through this process.

We are primarily composed of freshman and sophomore students, and actively encourage interested students to join. We do not have any major requirements, and in past years have had a wide range of engineering majors, as well as members from the Colleges of Science and Liberal Arts.

ATEx has received recognition for its accomplishments at a university-wide level; footage from our Spring 2013 launch of the Hokie Bird in the upper atmosphere was featured in the 2014 Virginia Tech "Hands On, Minds On" commercial shown at Virginia Tech football games and on ESPN.

Tasks

  • Design side panel cutouts, and redesign corner brackets as necessary to make them more mass-efficient
    • We will use a combination of stress analysis in Autodesk Inventor and drop-testing with an accelerometer to test these designs
  • Fabricate and test servo-driven remote cutdown system in low-temperature environment
  • Ensure all CAD part files use parametric design for easier adjustment/manipulation in the future
  • Design and drop-test "shelf" payload mounting system
  • Finalize electronic specifications and dimensions
    • This is the penultimate step; the final bus design is based on the size of the electronics and payload
  • Complete full system assembly and possibly run test flight


Steps documenting our design process

Weekly Progress Report

 Date
 Mechanical Notes  Electrical Notes
 08/28/16
  • First meeting of the semester
  • Introduced new team officers
  • Reviewed status of payload from April 2016 launch (still stuck in tree near Floyd, VA)
  • Administrative stuff
 09/04/16
  • Divided members up into two groups, led by Anthony and Derrick
  • Each group was tasked with brainstorming a minimum of two ideas for possible tree-removal systems that could be included on board the system
  • They will present their ideas at the next meeting
  • Quick system overview
  • Timeline discussion
 09/11/16
  • Teams presented ideas
  • From group 1:
    • Teardrop-shaped payload
    • Lever arm mechanism
    • Expanding balloon "airbag" design
    • Trapdoor-rope design
      • Team agreed this was the most practical design
  • From group 2:
    • Attach parachute to bottom of payload instead of in-line with balloon.
    • Parachute has metal ring to prevent opening during ascent, but allow opening during descent.
    • Parachute and balloon can both be detached from bus structure.
  • Both groups have been given two weeks to build prototypes of their designs for testing.
 Meeting Goal
  • To maximize the amount of options available for the upcoming preliminary system design
 During the meeting
  • Requirements update (see below)
  • The affects of new requirements on the system
 Week's research
  • System component update driven by the new requirements
  • Sensor selection revision
  • Geiger counter or digital dosimeter research
  • Data logging and storage research
 Extra research topics
  • SSTV, APRS, Trackduino, general familiarity with Arduino platform
 09/18/16
  •  Subteams met and worked on two different drop test systems
    • "Teardrop" group went to hardware store to find parts for testing;
    • "2-Cutdown" group looked at gimbaling devices
  • Ilya suggested aiming to launch during solar eclipse in August 2017
    • Team members discussed likelihood of being able to meet launch goals, considered amount of testing that will be required to be ready in time.
 Meeting Goal
  • Draft sensor selection 
  • Resolve BBB vs Arduino
  • Decide on the data we are transmitting
 During the meeting
  • Sensor, geiger counter data storage presentations
  • Component selection (results below)
  • Aruino + RTOS brief into
 Week's Research
  • Arduino and RTOS hands-on practice and evaluation
  • GPS research (How do we locate the payload?)
  • APRS + SSTV research
Challenges
  • Complexity (knowledge and resourses required to build)
  • Power draw, size and weight
  • Flexibility (how quickly can we go from order to working module? how well it integrates into the current system)
 09/25/16
  •  Derrick's team presented their prototype for a teardrop-shaped system bus
    • they have conducted testing with accurately-weighted system and have had some success with it self-leveling and falling out of trees;
    • cheap prototype build: parts were $3.25
    • next testing will compare teardrop geometry with cube geometry to see if either gets stuck in branches more often;
  • Anthony's team 
    • Design is a servo-controlled parachute release that will be operated in person at landing site;
    • Prototype completed; testing will be done at end of meeting.
 Meeting Goal
  • Radio design decisions
  • Pick SSTV, APRS tracker
 Week's Research
  • Radio design
    • Pick transmitter, antenna
    • System diagram
  • APRS Tracker
    • Cost and complexity analysis
    • Buying vs building
 10/02/16
  • Drop testing was conducted
  • Initially tried to climb tree and get payload with parachute to be stuck in branches
    • mild success
    • ended up tossing payload/parachute off of Whittemore Hall balcony into tree
    • testing inconclusive; did not get stuck as much as we had hoped to form a baseline
  Meeting Goal
  • Discuss current radio design
  • Figure out challenges and limitations
 Week's Research
  • SSTV and APRS integration
  • Can we use the same antenna and transmitter for SSTV
  • BigRedBee tracker research
    • Should we use old module for November launch?
    • Should we build our own tracker for November?
  • Arduino
    • Practice interfacing with MPU-6050 inertial measurement unit (I2C libraries, documentation)
 10/09/16
  •  Fall DTE Application is due in coming week; team reviewed budget request and practiced presentation
  • Team members looked into ways to model teardrop shaped payload to maximize aerodynamics and minimize drag
 
 10/16/16
  •  No meeting this week due to Fall Break. Members were asked to complete any unfinished AMP Lab training videos.
 
 10/25/16    
  •  Mechanical team members discussed design of Gimbal system for camera
    • Minzhen brought his own quadcopter gimbal system for reference
    • Team members specced out brushless motors and found items to purchase online
    • Currently working on 3D printing gimbal arms and other components; will be cheap to repair, since plastic parts will fail before motors
  • Reviewed request for Engineering Outreach Fund grant
  • Discussed possibility of outreach launch in Fall even though Campus Scouts launch fell through.
  • Also discussed plans for outreach event with InVenTs community in the spring
    • Plan is to teach freshmen in Galileo/Hypatia about Arduino basics, how to gather sensor data with microcontroller, how to launch weather balloon
 

Educational Value

Our design team's goal is to promote enthusiasm for engineering and atmospheric science, in the community and among our team members. The team organizes an annual outreach event, historically in the spring, where we invite students of all ages to participate in a balloon launch. Our outreach curriculum also involves school visits, where we work with primary school science teachers to educate young students about the scientific method and the engineering design process.

In the Virginia Tech community, we encourage all interested students to participate. Unlike most other design groups on campus, ATEx does not expect that students join the team with any prior engineering knowledge or technical skills, other than a desire to learn and contribute. We mentor new members and teach skills such as CAD Modeling, 3D printing, Microcontroller programming, and PCB design.


Design Decisions

Bus Structure Material

The bus structure is the main and most important feature of mechanical design. The structure consists of six rigid panels that are joined to form a rectangular box, which houses the electrical system, sensors, and GPS unit during launch. Historically, ATEx constructed the bus structure from 1/2" foam, which is very inexpensive, can be cut/machined with knives or a CNC router, and has favorable insulation and shock absorption properties. Downsides to foam are the bulkiness due to the low density, as well as the fact that the team's ultimate goal is to use the platform as a near-earth prototype for a CubeSat modular satellite, so designs have moved towards thinner wall panels that could theoretically be used in near-space missions. 

In more recent years the mechanical team has primarily used 1/8" plywood sheeting for our bus structure wall panels. Advantages are that it is fairly strong, inexpensive, and easy to machine using a laser cutter or Dremel. However, during our Spring 2015 launch the payload landed on an asphalt driveway (at a descent velocity of 6 m/s) and one side of the bus structure buckled, damaging the panels as well as the electronics inside.

As a result, this year the team has been considering alternative materials. The two that we narrowed in on were:

  • Balsa wood: very low density; inexpensive; easy to machine; good thermal properties. We were considering this partially because we hoped the balsa wood would cushion the payload in the event of a hard drop, and act like a "crumple zone" in a car, absorbing most of the impact. However we drop-tested multiple balsa payloads and noticed that it still has a tendency to crack and fail around the corners, which is not ideal.
  • Carbon fiber: we originally discounted carbon fiber due to the fact that it is either very expensive to order, or requires extra equipment and training to do in-house fabrication. However, we found a Chinese manufacturer from which we can order custom machined carbon fiber panels for only about $20. Drop-testing results were optimal; even after landing corner-first on concrete with a 2 lb payload, the panels showed almost no wear or damage. The only downside is that shipping takes about 2 weeks, so it requires more advance planning on the part of the team when it comes to panel testing.
After consideration of both options, the mechanical team has opted to use carbon fiber as the panel material of choice.

Remote Cut-down Process

The FAA mandates that weather balloons with payloads exceeding 6 pounds or that use cords with a >50 pound break force are required to have at least two independent cut-down processes. Our current design does not put us in this category, however the mechanical team has decided that implementing a secondary cut-down system is important, as it gives the team more freedom in the overall design in case we need to run over the FAA minimums.

Because we use a helium-filled latex balloon, our primary cut-down system is the balloon itself since it will burst after it gets high enough in the atmosphere. We have some control over the burst altitude of the balloon by controlling the diameter of the balloon and the volume of helium inside it, however we have less control over the path the balloon travels. In the event that the payload is blown towards a major city or the Chesapeake Bay, or alternatively the Appalachian mountains, we want to be able to remotely pull down our payload to avoid losing it or causing property damage.

Our previous cut-down design was based around nichrome wire, a nickel-chrome alloy with high electrical resistance that heats up when a voltage is applied across its length. A length of wire was wrapped around the line tethering the payload to the balloon, and when the flight time reached a pre-set amount (90 minutes) a switch was closed and the nichrome wire heated up and melted through the paracord line, allowing the payload to parachute to the ground. The advantages to this design were that it was fairly simple and had no moving parts, and was reliably tested multiple times in the lab. However the main downside is that is required a large amount of power for a prolonged period of time, which meant that a large battery had to be added to the electrical payload, and increased the system mass significantly. With that in mind, the mechanical team looked this year to design an equally lightweight and reliable cut-down process that only required a fraction of the power to run.

We considered two main servo-driven designs:

  • Pin release: this system consists of a pin threaded through a hole in a 3D printed bracket. The primary cord connecting the payload to the balloon is tied to this pin, so in order to cut down the payload the servo retracts the pin and allows the balloon cord to disconnect and float away. Advantages to this system are that it is lightweight and hopefully easy to install, and is fairly inexpensive as it only uses a small servo and 3D printed ABS material.
  • Slicing mechanism: this is also controlled by a servo, however it relies on moving a razor blade to cut through the connecting cord. This design is less desirable due to the potentially dangerous nature of mounting a cutting blade to the top of the payload; additionally it requires more testing and higher force
    from the servo to cleanly cut through the cord, and limits the options for the cord, as some materials may be harder to sever.
The mechanical team has investigated both designs and has determined that the pin release mechanism is both simpler and safer to implement, so that option has been incorporated into the system design.

Modular Electrical System Mounts

The balloon payload consists of electrical and mechanical systems that need to interface adequately for a successful launch; the electrical system depends on the mechanical structure for protection from the elements and from damage during flight and landing, while the mechanical cut-down system needs power from the power distribution component. 

The main goal for systems integration is to create a physical structural support for the electrical system. This will be accomplished through a modular system of shelves inside the bus structure. The electrical system PCBs can be mounted to these shelves and slotted into the bus structure prior to flight. In the event of any last-minute changes, the panels can be slid back out for ease of access. This is a vast improvement over designs from prior years, that involved sealing the electronics inside the bus structure with tape, glue, or hard-to-access nuts and bolts; there have been multiple instances where balloon launches have failed to record data or video due to mistakes during the assembly procedure, an easily preventable problem that the team wants to avoid. Additionally, this shelving system will save time and expenses during the design process since it will be faster to construct and refine the mechanical system design around the electrical payload if the electronics can be mounted and removed with ease. With that in mind, systems integration is critical to the success of the project.

Two candidates were considered for Systems Integration design:

  • Friction-fit panels: this design is as it sounds: the electrical components are mounted to panels, likely made from plywood. For each panel there will be a set of 3D printed brackets with a groove down the long axis. The width of the groove will be slightly smaller than the thickness of the panels. These brackets will be bolted to the inner sides of the bus structure, and the panels will be mounted by sliding them into the brackets for a snug fit. The main upside to this design is the simplicity. There are no moving parts or extra components other then the plywood and 3D printed ABS pieces, so there are very few points of failure. The main downside is that it might take iterative testing to reach a satisfactory level of friction for the fit.
  • Spring-loaded panels: this is a slightly more complex design. Instead of relying on friction to keep the electrical panels in place, there is a hook-and-spring system built into the mounting brackets. When the panels are slid into place, the spring compresses and the mechanism locks the panel in place. The springs can be engaged to pop the panels back out of the bus structure. This design, if working smoothly, can make panel insertion and removal much easier, especially for pre-launch assembly, however the fact that there are multiple moving parts and 3D printed pieces under stress means that there is a much higher anticipated failure rate.
Due to the importance of systems integration to the overall success of the ATEx mission, the team has opted to go with the friction-fit design for its much lower expected rate of failure.


Electrical Systems

Updated System Requirements For Electrical Systems

  • Last year payload relied on a reflow process for PCB assembly
  • Currently, the team does not have access to a reflow lab
  • It was decided to minimize risks and rely only on hand-solderable components for the initial prototype
Rethinking the core systems

   BBB (2015/2016 implemetation)  Arduino (alternative)
 Pros
  • Individual task oversight (failure of one system does not affect other data)
  • Coding and debugging is done on the board itself
  • Easy data storage
  • Low power consumption (for an embedded linux system)
  • Easy to pick up with zero experience
  • Low power consumption (on the order of several mW)
  • Potential to utilize several processors
  • Libraries and frameworks are readily available
 Cons
  • Steep learning curve, especially for younger members
  • Only small portion of the processor's potential is actually used
  • Somewhat large comparing to the rest of the sensors and components
  • More difficult to make completely failsafe (not impossible)
  • Limited processing power
  • Lacks proper debugging tools
  • Sometimes requires experience with oscilloscope and other diagnostic tools
 Conclusion 
  • Arduino + RTOS
  • Currently (see 09/18) evaluating ease of use, flexibility and potential failure points
  • SDFAT library for direct data storage to SD card

Current Electrical System Design

Final Design ‎(Draft)‎



2015/16 System Design

System Power Budget


BOM + Component costs

Electrical Bill of Materials & Costs:


Sensor Bill of Materials:

Mechanical Bill of Materials and Costs:

Timeline

  • Preliminary Design Review: November 2017
    • Initial design decisions with justification
  • System Testing: January - March 2018
    • Full testing of system integration and assembly
    • Potential test launch
  • Outreach payload launch: Novemeber 2017
    • Outreach payload test may be combined with test launch. Details are pending.
  • Critical Design review: Week following Spring Break 2018
    • Detailed design presentation
  • Spring Outreach Even and Data payload launch: Mid April 2018
    • Full system launch
    • Post-launch system and data evaluation

Useful Links

Facebook page:                         https://www.facebook.com/VirginiaTechATE
Preliminary Design Review:       https://goo.gl/ZPZQ4L


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