Hello out there,

I'm working on a research project to develop a rocket engine and am looking for a cheap method to collect data on vibrations generated from unstable combustion and resonance.

I'm expecting a range of frequencies from a few hundred Hz up to at least 10kHz or higher. The motor will be mounted on a rigid test stand so the motion induced by these vibrations should not be that large. Just doing a simple F=m*a calculation based on F(thrust)=2224.1N and m~5kg I get an average a of about 45g. If the combustion is very unstable the thrust will chug and produce much larger thrusts so I think its reasonable to assume maximum Acc of around 100-150g. (These calculations are assuming my rocket is not rigidly attached to the test stand, if it were the Acc would be much less due to the larger mass value in F=m*a.

I'm considering using the 250g ADXL 193 to capture this data but I'm not sure how to interpret the sensor's capabilities. The datasheet says it has a resonance frequency of 24KHz and a clock frequency of 400kHz. I'm assuming this sensor should be able to capture all the vibrations I'm looking for up to its resonant frequency? I'm really only concerned about vibrations under 15kHz as higher frequencies will not effect the stability of the rocket or cause structural design problems.

http://www.sparkfun.com/commerce/produc ... ts_id=9332

The analog data must be fed into my LabView software for analysis so I'm looking at ADC solutions and am starting to fear that I will need to build my own due to the high price of good quality converters.

I was originally looking at a 12-bit ADC converter that ran at 115.2kBaud serial to USB.

Some other chips from Ti or AD capture 16-bit at over 1Mips for about $30 so I may end up designing the ADC around one of these chips.

Any thoughts would be greatly appreciated!

<>Steve

I'm working on a research project to develop a rocket engine and am looking for a cheap method to collect data on vibrations generated from unstable combustion and resonance.

I'm expecting a range of frequencies from a few hundred Hz up to at least 10kHz or higher. The motor will be mounted on a rigid test stand so the motion induced by these vibrations should not be that large. Just doing a simple F=m*a calculation based on F(thrust)=2224.1N and m~5kg I get an average a of about 45g. If the combustion is very unstable the thrust will chug and produce much larger thrusts so I think its reasonable to assume maximum Acc of around 100-150g. (These calculations are assuming my rocket is not rigidly attached to the test stand, if it were the Acc would be much less due to the larger mass value in F=m*a.

I'm considering using the 250g ADXL 193 to capture this data but I'm not sure how to interpret the sensor's capabilities. The datasheet says it has a resonance frequency of 24KHz and a clock frequency of 400kHz. I'm assuming this sensor should be able to capture all the vibrations I'm looking for up to its resonant frequency? I'm really only concerned about vibrations under 15kHz as higher frequencies will not effect the stability of the rocket or cause structural design problems.

http://www.sparkfun.com/commerce/produc ... ts_id=9332

The analog data must be fed into my LabView software for analysis so I'm looking at ADC solutions and am starting to fear that I will need to build my own due to the high price of good quality converters.

I was originally looking at a 12-bit ADC converter that ran at 115.2kBaud serial to USB.

Some other chips from Ti or AD capture 16-bit at over 1Mips for about $30 so I may end up designing the ADC around one of these chips.

Any thoughts would be greatly appreciated!

<>Steve