Posted by serge petiot on December 4, 2009 at 1:01am
which Reference Vector should I use?...Dear All,Since I'm new here, allow me to introduce myself: Name is Serge and I am a Embedded Hardware/Software engineer. As I am into experimental rocketry, I decided to built an IMU specific to Rockets. I have built a board based around a dsPIC33FJ128MC506 (runs at 40MIPS), and it has a 3D magnetometer (MicroMag3), one IDG500, one IXZ500 gyro along with a MMA7340 accelerometer. Of course, it also measures T°, Atmospheric pressure, and is able to interface to a Pitot daughter board, and GPS. It has 6 low-side 12V outputs for igniters ans 6 PWM servo outputs. Now, the time has come to write the Software, so I have read as much as I could on the subject of DCM (thanks Mr Premerlani and Bizard, great paper). Now, a point that is really bugging me is: I need 2 reference vectors to correct the gyros drift. I cannot use the accelerometer since it is absolutely useless in a rocket (at least during boost and coast phase) and the GPS is of no use as well but at least I got reliable Magnetic North. My question is: can I get by using only one vector to correct the gyros?
I think I'm moving tot France! I have been involved in Amateur/Experimental Rocketry for about 30 years. In my adult life I pursued rocket motor development as a primary focus of my interest. Designing and testing over 20 different motors ranging from E to I class motors. All have been based on amateur sugar/sugar-alcohol based propellant, primarily of the sorbitol and dextrose variety. I went to motor development as a focus primarily because I coulld do it legally with the proper limits and permits. I would have pursued guidance development, however here in the states guidance systems are prohibited for amateur rocketry. Only commercial rocketry is allowed the use of guidance systems. We can obtain permits to launch a vehicle to "space" but no guidance.
"Tripoli and NAR safety codes also require that no rocket contain guidance systems, vertebrate animals or be launched more than 20 degrees from vertical. A complete review of all NAR safety codes may be found at www.nar.org ; Tripoli safety codes may be requested at www.tripoli.org. NFPA code 1122 refers specifically to Model Rocketry; NFPA code 1127 covers High Power Rocketry. For more information on the NFPA and to see codes 1122 and 1127 go to www.nfpa.org. "
Have fun, fly safe, and bore lots of holes in the sky!
You actually have two vectors.
By looking at the change in gps x,y,z velocity from fix to fix you have an average acceleration vector.
You also have a measured acceleration vector.
These two vectors should align.
Probably much easier to do with a 10Hz GPS.
Replies
I think I'm moving tot France! I have been involved in Amateur/Experimental Rocketry for about 30 years. In my adult life I pursued rocket motor development as a primary focus of my interest. Designing and testing over 20 different motors ranging from E to I class motors. All have been based on amateur sugar/sugar-alcohol based propellant, primarily of the sorbitol and dextrose variety. I went to motor development as a focus primarily because I coulld do it legally with the proper limits and permits. I would have pursued guidance development, however here in the states guidance systems are prohibited for amateur rocketry. Only commercial rocketry is allowed the use of guidance systems. We can obtain permits to launch a vehicle to "space" but no guidance.
"Tripoli and NAR safety codes also require that no rocket contain guidance systems, vertebrate animals or be launched more than 20 degrees from vertical. A complete review of all NAR safety codes may be found at www.nar.org ; Tripoli safety codes may be requested at www.tripoli.org. NFPA code 1122 refers specifically to Model Rocketry; NFPA code 1127 covers High Power Rocketry. For more information on the NFPA and to see codes 1122 and 1127 go to www.nfpa.org. "
Have fun, fly safe, and bore lots of holes in the sky!
By looking at the change in gps x,y,z velocity from fix to fix you have an average acceleration vector.
You also have a measured acceleration vector.
These two vectors should align.
Probably much easier to do with a 10Hz GPS.