The First test was done in Instituto Superior Técnico (IST). The idea was to fill a balloon, add a number of different equipment to test (sensors, microprocessor, communication systems, inertia wheel, etc) and let it go always tied to the rooftop of IST’s tallest building.___________________________
- Test and verify communication with the payload using Xbee.
- Test the on-board data storage device (microSD card).
- Test GPS (android device).
- Test the actual lifting capability of a balloon.
- Test the influence of the inertia wheel in the stability of the payload
- Test the proceedings of launching a balloon.
- Main Payload = 860g
- Filled Balloon = 600g
- Total = 1460g
- Xbee 2.4 GHz serie 1
- 1 pressure sensor
- 1 3-axis accelerometer
- 1 magnetic compass
- 1 temperature sensor
- 2 Cameras (range: visible)
- 3s LiPo 11.2V 2000mAh
- Maxon Motor EC 32 3 watt
- 1-Q-EC Amplifier DEC 24V/1A inverter and controller
- Inertia wheel
- Android Smartphone
How it works
The main flight computer was a custom PCB with an ATmega328 running the arduino bootloader. It receives data from a temperature sensor, a pressure sensor, a magnetometer and a 3-axis accelerometer. All data is stored on an on-board microSD card. The flight computer was also sending data through Xbee to a base station. The inertia wheel had a separate controller from Maxon Motors. All systems are powered by a Lithium 3S LiPo battery . The android device has its own battery and was logging the GPS coordinates.
The ATmega328 running the arduino bootloader is programmed in C language and the main software loop runs on the following instructions:
- Reads sensors and converts data,
- Sends data through the XBee using serial,
- Stores data to the microSD card.
Before the “Launch”
The word launch is in quotation marks because this was not going to be an actual launch. In fact the idea was to have the balloon always tied up to the ceiling and test equipment that we also didn’t want to loose.
Prior to the day of the “launch” we prepared all the equipment.
- Sensors and data storage,
- Rigid Styrofoam case for the different equipment,
- Camera trigger system,
- Xbee communication with ground station,
- Inertia wheel controller.
It was a warm and cloudy day and soon in the afternoon we packed the equipment and headed to the top of IST’s South Tower with the authorization of the building manager. Once there, we started to fill the balloon and finalizing the preparation of the payload, the whole process was delayed by our inexperience and also because we were constantly trying to figure out if we didn’t forget something. A checklist would be very useful.
Even though we manage to assemble the whole system and launch the helium filled balloon tied by a string with about 10 meters. The ascent ratio was very similar to what it was expected and the balloon was stabilized there for about 30 min transmitting data through the XBee protocol.
The After “Launch”
After 30 minutes we recollected the balloon and took the SD cards in both cameras and flight computer. We got some cool pictures of Lisbon and IST. Plus the datalog system worked correctly. Several engineering contraptions were tested and despite the fact that many of them revealed to be unusable in an actual balloon launch (e. g. inertia wheel, android device, XBee, etc) this was our first actual test with balloons and the knowledge we took from it was very important. We still have to develop a lot of work to correct and improve this design.
Pictures and Video
More pictures and/or movies can be found in the gallery section of this website – here.
The actual data obtained was of no interest to us. We were more interested in verifying if the readings were correct and the controller’s ability to store multiple sensor readings in the microSD card.
- Launching balloons is a complex process that requires good team coordination.
- Delegating separate launch tasks and responsibilities would improve the process and avoid mistakes.
- The camera mechanism to take pictures is faulty and heavy. A GoPro should be more adequate.
- The lifting capability of the balloon was in concordance with what was calculated.The data storage was successful.
- The communication system was successful but it cannot be used in a real flight. APRS and RTTY is probably the way to go.
- The android device GPS was very accurate but it’s also a heavy solution. Better solutions available.
- The Inertia wheel effect in the stability of the payload was almost irrelevant, the inertial moment provided was not enough to actually produce effect, especially if we take into account its added weight.
- The lithium battery didn’t show any type of problems.