We have entered the UK Aerospace Youth Rocketry Challenge.
In this challenge the aim is to launch a rocket to as close as possible to 775 feet and have the rocket land under a parachute within 40-43 seconds after motion at launch.
There are also several other design criteria that must be obeyed. See link below for more information :
Many teams achieve this objective by designing a rocket to reach apogee at this altitude and trim the parachute to allow their rocket to land in the time window. However this has proved to be inaccurate with some of the best results still being over 20 feet off the target. This forced us to design a more accurate way of reaching near to exactly the specified altitude and thus also staying within the time window by trimming the parachute.
We are using an Arduino Micro, to control a barometer/altimeter, an SD card reader and a digital servo.
The design uses a pressured gas deployment system:
As shown in the picture, we have a gas chamber (seen as red) which, via the tyre valve is pressurised to 50psi. The chamber connects to our electronics payload which controls a designed servo controlled valve. The other side of the valve connects to a syringe which is mounted in the rocket in such a way that as soon as the valve is opened and the pressurised gas fills the syringe, the plunger fires out in less than 200 milliseconds, thus pushing the parachutes and 2 parts of the rocket apart.
The code consists of over 331 lines and uses 90% of available storage on our arduino.
After connection to power, the code firstly pauses for a set number of seconds before initializing its setup to allow us to pressurize the chamber and put the rocket together.
After this period has elapsed, it works out a ground measurement as the altimeter sends altitude above sea level.
It then waits for launch, there are 2 launch criteria. one is more accurate and faster in responding but we have the other as a failsafe:
- This works out a speed of the rocket. If this speed passes a set threshold which we have worked out to be high enough to not initiate a false lauch but low enough to launch the system when the rocket starts to move.
- The second is a failsafe. This launches the system when the altitude reading reads above 10m from ground.
The system has 4 deployment criteria, again, one is the most accurate and the others are failsafe:
- This predicts when the rocket reach the desired altitude and deploys a certain time before e.g. 700 milliseconds, this allows the parachute to deploy and rocket to slow down to reach the exact altitude desired.
- This is a failsafe. The parachute is deployed as soon as it is over the altitude desired. This will lead to a higher max altitude than desired and thus is used as a failsafe.
- This is a failsafe. The parachute is deployed as soon as it detects the rocket is descending, thus preventing a ballistic decent, even if the rocket does not reach the desired altitude.
- This is a failsafe. The parachute is deployed a certain number of second after the system detects a launch.