diyaerospace
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- Sep 21, 2021
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Hello!
Me and some of my friends started working on a rocket that will use a variable drag brake system to control its altitude.
My idea for this was to use a pressure sensor to read the altitude of the rocket in real time and compare it to the rocket's ideal altitude. I will model the ideal altitude as an array in the flight software, calculating the ideal altitude will be done by looking at altitude points at certain time steps in rocksim. Using the difference in the actual and ideal altitude I can generate an error, and I plan to use a proportional control algorithm to generate angles for the drag brakes.
I have started writing a simulation in Arduino to model the rocket's flight and calculate the ideal gain for the control system. I will use a software in the loop test to validate the flight software before I fly it on this rocket. We plan to have our first launch in early October.
Here are some issues I have encountered with my Arduino simulation. (I have solved a lot of these, I just thought it would be cool to share things to watch out for)
1) Drag equation
Since my whole system depends on drag force I have to precisely model drag in my simulation. The equation on the NASA website doesn't work for me. The rocket flies way higher and its coasting time is far too high. I found this equation that works a lot better for me.
https://www.grc.nasa.gov/www/k-12/rocket/termvr.html
2)Cd changes
In most model rockets the coefficient of drag is a constant. But because we change the rocket's frontal area, the Cd also changes. I am still working on this aspect of the simulation.
Feedback would be appreciated,
Walter
Me and some of my friends started working on a rocket that will use a variable drag brake system to control its altitude.
My idea for this was to use a pressure sensor to read the altitude of the rocket in real time and compare it to the rocket's ideal altitude. I will model the ideal altitude as an array in the flight software, calculating the ideal altitude will be done by looking at altitude points at certain time steps in rocksim. Using the difference in the actual and ideal altitude I can generate an error, and I plan to use a proportional control algorithm to generate angles for the drag brakes.
I have started writing a simulation in Arduino to model the rocket's flight and calculate the ideal gain for the control system. I will use a software in the loop test to validate the flight software before I fly it on this rocket. We plan to have our first launch in early October.
Here are some issues I have encountered with my Arduino simulation. (I have solved a lot of these, I just thought it would be cool to share things to watch out for)
1) Drag equation
Since my whole system depends on drag force I have to precisely model drag in my simulation. The equation on the NASA website doesn't work for me. The rocket flies way higher and its coasting time is far too high. I found this equation that works a lot better for me.
https://www.grc.nasa.gov/www/k-12/rocket/termvr.html
2)Cd changes
In most model rockets the coefficient of drag is a constant. But because we change the rocket's frontal area, the Cd also changes. I am still working on this aspect of the simulation.
Feedback would be appreciated,
Walter