Re: [Paparazzi-devel] question about paparazzi on sounding rocket

[Christophe De Wagter]

Standard Paparazzi gear using u-blox gps will measure up to 50km high and 500m/s with 4g accelerations. Beyond these limits you might loose track. The max speed represented in paparazzi in float is unlimited and in fast fixed-point integer mode the fiedpoint FRAC is 19 on 32 bits so speeds up to 8000 m/s are still possible. For gyro's and accelerometers paparazzi uses ADXL345 most of the time with a range of "only" 16G but any analogue accelerometer (like the 250g ADXL193) can be connected without additional programming and any other gyro can be added with code available for a significant number of sensors. Paparazzi has controllers for many types of vehicles including "thrust-vectoring-vehicles" code (rotorcraft, prop-hanging planes but probably also rockets), with euler or even quaternions, but using them differently than in the default firmware will require some programming. I expect that rotorcraft firmware can be used as-is on rockets. For additional own code paparazzi has easy to use extra modules to put all your personal code.

Trouble: logging is still not native on the same microcontroller (but many sollutions exist to log the serial output)

GPS speed and acceleration limits do not guarantee a full log. (but probably when logging accelerometers too it can be reconstructed)

gyroscopes readings will degrade with vibrations and high G-forces and special accelerometers might be needed (depending on your size of rocket)

-Christophe 

On Tue, Feb 14, 2012 at 8:42 AM, Hector Garcia de Marina <address@hidden> wrote:

Hi Florin,

just for clarifying. For measuring Mach, you will need a FADS system (pressure sensors) and get around the problems about Temperature and Density of the atmosphere (speed of sound). Actually, for control purposes, the variable is usually the dynamic pressure (from FADS system).

GPS does not measure Mach (and of course Mach is not a velocity, it is an adimensional number xD).

About employing MEMS sensors for an inertial navigation in a rocket (may I ask what rocket is?) where the environment is hostile (heavy acoustic vibrations, heavy mechanical vibrations, etc). I do not know the current available devices, but I guess that you will need more than simple MEMS low-cost sensors for a decent navigation.

About GPS measuring Ground Speed and ECEF Position at high velocity, I really do not know about how the accuracy is affected, Doppler effect, etc. But it seems that you need an expensive GPS module.

Héctor.

On Tue, Feb 14, 2012 at 2:34 AM, Chris Gough <address@hidden> wrote:

> Does the paparazzi code accomodate velocities as large as Mach 2- Mach 3?

I don't know, sorry (don't see why not though, try it in
simulation...). Maybe someone else can comment on that.

Do I understand you correctly:
 * the rocket will go directly where you aimed it, it's not actively "navigated'
 * the autopilot is not responsible for maintaining vertical attitude
 * your instruments require a constant orientation (roll in the
rocket's frame of reference) during the preiod between boost and apex.
 * your experiments require position and attitude logging during the
same flight phase.

Chris Gough


> Best regards,

> Florin Mingireanu
>
>
>
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