- Feb 6, 2009
- Reaction score
You only need the accels for launch detect.The MPU9250 board DOES have a magnetometer, but if you think about it you don't really need it. You aren't trying to figure out which direction your rocket is pointing, just what the tilt is. Using the accelerometer to give you the tilt on the pad and the gyros to correct it in flight is the easiest way to do this, and it's not dependent on the velocity or acceleration of your rocket. For that matter, you don't need to worry about the z-axis gyro either, it doesn't affect the tilt.
You don't want the rocket to fly straight up but to stay pointed in the same direction that it was on the pad. This way you can adjust its trajectory based on winds so that it has a better chance of landing where you want it to. Plus going straight up messes with the best practices of angling the rocket away from the flight line.
All the gyro axes are required because any rotation around the longitudinal axis changes the orientation of the other two.What was providing tilt in the north-south plane a moment ago could now be east-west.
I have a little project on the bench at the moment to record MPU-9250 data at high speed. Once I get that code working I will dust off what I remember about quaternions.