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Best flight computer/software package for motor and rocket characterization

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kclo4

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Sorry for the long title. I am getting back into rocketry after another 5 year hiatus and looking to pick up a solid flight computer. I would like one that has an accelerometer and baro and I it would be preferable to have a nice software package for configuration and analysis.

Mainly I would like to be able to back out Cd info of the rocket vs. speed and at the same time be able to back out motor thrust for characterization/verification purposes. If a software package could do it all for me without matlab/excel/whatever that would be swell.

Was leaning towards the Featherweight raven as a good bang for the buck, can the software handle this duty?

Will likely build a Eggtracker and maybe a egg timer as backup but that doesn't help me with accelerometer data.

Thanks!

Pax
 

mikec

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Was leaning towards the Featherweight raven as a good bang for the buck, can the software handle this duty?
If you're talking about deriving Cd and motor thrust curve automatically, no, the Raven software doesn't this easily, although you could export the data and do it with external software.

I'm not sure if any altimeter currently in production can do this, maybe the MARSA?
 

Buckeye

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This is a good start:

http://www.rocketryforum.com/showthread.php?121323-Altimeters-Comparison-guide

Search this forum, and you will get a million opinions.

I have the same objectives as you, and I have come to the conclusion that the Featherweight is probably the best choice, but with a higher learning curve. The MARSA is also good, simple, and the inventor is active on the forum.

However, I think we all put too much faith in the accel data. Each computer has its quirks and limitations. Using flight data to back-calculate performance is fun, practical, but totally wrong from an engineering perspective. The correct way to get Cd is in a controlled lab like a wind tunnel or CFD. The correct way to get motor thrust is from a firing stand. :2:
 

ksaves2

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If you're talking about deriving Cd and motor thrust curve automatically, no, the Raven software doesn't this easily, although you could export the data and do it with external software.

I'm not sure if any altimeter currently in production can do this, maybe the MARSA?
You're correct the MARSA 54 I believe can do it: http://www.marsasystems.com/ Maybe the Tele or Easy Mega? But the Marsa 54L is likely more cost effective. Kurt
 

mikec

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Yes, the MARSA can do this as a beta capability of the software. Keep in mind that backing out Cd and thrust curve could be done with any altimeter with an accelerometer in theory, but most of them don't have software to do it (the old ARTS was the best example but it's out of production). This has been talked about for the Altus Metrum products but never implemented AFAIK.

If you just want a capable, highly flexible accel-based altimeter the Raven wins IMHO for price-performance. Someone could write analysis software for the Raven.
 

Onebadhawk

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Marsa 54L. ....
Check the Marsa website....
Read what it can do there.....

Teddy
 

kclo4

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Yeah, seems like Raven is pretty flexible. I haven't seen the MARSA name thrown around much yet. I probably should just write a matlab script to do post processing of flight data.
Seems like real life flight data would be the best way to characterize a rockets performance vs. a wind tunnel. And the motor characterization would be more verification for me just to make sure things are operating as they should.
 

Buckeye

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Yeah, seems like Raven is pretty flexible. I haven't seen the MARSA name thrown around much yet. I probably should just write a matlab script to do post processing of flight data.
Seems like real life flight data would be the best way to characterize a rockets performance vs. a wind tunnel. And the motor characterization would be more verification for me just to make sure things are operating as they should.
The Cd post-process is pretty simple. During coast phase:

0.5*rho*Cd*A*V**2 = m*a

integrate your a to get V
integrate V to get h
look up rho vs. h from standard atmosphere
m and A are easily measured at home

Though, this may start another argument that another m*g belongs in the equation!

Anyway, the accuracy/interpretation of the acceleration from the computer is the biggest concern. I have seen some wacked data.
 

jderimig

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Characterizing a motor with flight acceleration data is pretty straightforward. The motor characterization feature in the MarsaConnect program will generate a thrust curve, total impulse of the motor and estimate Cd of the rocket. I routinely get thrust curves and impulse of commercial motors within their certification tolerances.

However you can perform the same calculations in Excel, a good acceleration measurement is all that is required. Some altimeters have better acceleration measurement systems than others.

To use this method some rocket designs are better than others. Characterizing a motor from flight data as a bonus to a general rocket you flew is not as good as designing the rocket specifically for motor characterization.

For example a very draggy rocket that reaches close to terminal speed and stay low would be the best case. Saucers would be good. Cd calculation would be more accurate since drag force will be varying less during the boost. Minimum diameter rockets that have Mach transitions and go very high would not be the best profile for characterizing a motor.
 

ksaves2

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Wow, Does that mean for a small motor a saucer would be a good workhorse to characterize a mix for a smaller diameter case? That is price effectively cool!
Although I've seen some mixes quoted a lower Kn for use in larger diameter cases in the past. Have a payload bay for the MARSA54L and pop a chute at apogee for an assuredly soft landing for the electronics. Kurt
 
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