Altitude Control System

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Project Overview

3.1. Project Description Small-scale HAB flights (≤3000g latex balloons) are historically dependent on local conditions. HABs are a passive vehicle primarily controlled by prevailing winds. For safety, improved experiment-dependent data collection and flight control, the utilization of an altitude control system offers the possibility of longer and more effective missions. Members involved in this project will research, design, build, lab test and perform in-flight proof of concepts of their system. Maintaining a target altitude within a range of ±150m over 30 minutes is the goal of this project. Possible approaches include controlled pressure venting and ballast management.

3.2. Target Goals

3.2.1 The system will need to reach and maintain a specified target altitude and maintain that altitude within a range of ±150m over 30 minutes.

3.2.2 The system will be able to actively achieve an ascent velocity alteration from the average flight baseline of ±20%

3.3. Interests and Skill Sets Aerospace engineering, electronics, microprocessors and atmospheric science.

3.4. Team Participants

3.4.1 Project Lead
3.4.2 Mechanical Designer
3.4.3 Programmer
3.4.4 Project Assistants

Project Sub Goals

  • Determination of Control Authority
    • gas venting rate
    • ballast requirements
  • Programming of arduino
    • GPS altitude reports
    • servo control
  • Ballast
    • sand or propylene glycol?
    • design of initial ballast valve/tank
    • materials collection
    • prototype construction
    • testing of flow rate
  • Lifting gas vent
    • initial vent design

References

Article on flight characteristics of a rubber balloon

Leak rate for a balloon

Scientific Ballooning Handbook Part 1

Scientific Ballooning Handbook Part 2

Another project using a valved balloon venting system

Abstract of balloon buoyancy control system

Project Reports

10/3/2012-- Today we determined what our goals would be for the upcoming October 27th launch. We decided to focus on the flow rate of sand, our chosen ballast material. It was decided that sand is a more viable option than liquid ballast because of the ethical restrictions on toxic and/or flammable antifreeze materials. Also, a liquid would be subject to volume change due to the change in environmental pressure more so than sand. During our tests, we observed the the flow rate of 2kg of sand through various sized holes drilled through bottle caps. We also tested the flow rate of hyper-cooled sand that was chilled by liquid nitrogen to simulate the effects of temperature at high altitude. In addition, we discussed the possible designs of a ballast tank and valve system that would allow for a controlled release of ballast during flight. Nicknamed The Cheese Wheel, our design consists of a plexiglass cylinder with a hole cut in the top that has its rotation controlled by a Stepper Motor hooked up to an Arduino. The rotation acts as a start/stop for the flow, while the size of the hole in the top controls the flow rate.

By IMSA Interns 10/3/12

We think we have a stepper motor shield that is able to work with an arduino. Next we need to find a stepper motor to satisfy the following minimum requirements:

  • The stepper motor should be able to turn a minimum of 5lbs
  • Turn greater than or equal to 180 degrees
  • Accurate to better than or equal to 3 degrees
  • the motor must run on 9 volts max
  • the motor must weigh less than or equal to 200g
  • the motor must draw 1 amp of power max
By AFA Volunteers 10/3/12

Today we started building our CHEESE (Controlled High Elevation Escalating Sand Excretor) wheel. While testing our flow rates last week, we found that a 9.6 mm aperture would give a flow rate of approximately 15 g/s. This flow rate gives us enough time for the balloon to rise and does not become clogged. This week, we determined that the volume of the 2kgs of sand that we will be using is approximately 1160 cm3 or 1.16 liters. The torque of our mechanism when full is 2.75 N*m, or 2.03 ft*lb, which will help the students from AFA to determine which stepper motor would satisfy the requirements for our project. Then we used this number to determine the diameter for our ballast container. We found that an interior diameter of 28.4 was optimal. We then began to build the wheel out of 3mm thick plexiglass and 3mm thick black bendable plastic. We attached one of the circular faces to the plastic edging, but we will not be able to complete it until we determine what axle size would be optimal for the stepper motor.

By IMSA Interns 10/10/12

We built the Motor Shield for the Arduino. This stepper motor works with the Arduino Shield: Stepper motor that meets requirements Stepper Motor Specs:

  • Amps: 1.2A
  • Voltage: 4V
  • Weight: 350 g
  • Shaft diameter: 5 mm “D”
  • Steps per revolution: 200 steps
  • Holding torque: 3.17 kg-cm (44 oz-in)

Note: This torque rating is for holding torque. We think it should be strong enough since the ballast will always balance itself. Also see the torque chart on the specs page.

by AFA Volunteers 10/10/12

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