sipho

I have been assigned to develop a data collecting rocket for my electronics project. Info to be collected includes height, vibration, temperature,speed, distance and acceleration. This info should be displayed in a computer screen. how do I get on with this project

bmcculla

You should be able to get all the data you you specify with a single MEMS accelerometer for your sensor. http://rocky.digikey.com/WebLib/Moto...a/MMA1220D.pdf
is one that Digikey has for 15$. You can measure acceleration directly with this sensor. Velocity is the integral of Acceleration and distance is the integral of Velocity. Vibration will be the high frequency component of the signal.

All of these values can be stored into EEPROM on a microcontroller for readout later.

Brent

Klaus

You forgot about temperature and height :wink:
As to onboard stored data, that assumes you actually find the rocket after landing and it survived undamaged :wink:
Perhaps it would be better to use telemetry, at least you'd get data until the rocket expires one way or another :wink:

crust

However, performing a double integration on accelerometer data to obtain position doesn't work well in practice. Accelerometers are very noisy and that noise gets integrated, twice no less, into the position metric. I have had the most success with this by using a DFT to convert my data into the frequency domain. Then, hand-picking the bins to use for the integration while I compensate for buried noise. But this approach requires you to have a good idea of what frequencies your signal is composed of, sometimes that is not known. Most also dont extend below 10-20Hz. this is the proper way to analyze vibration however.

For the rocket specifically, its peak altitude is (usually) just when it is horizontal and starts to descend. An accelerometer is going to be most sensitive when it is on-axis. However, the rocket is going to move in an arc, so the accelerometer won't be reading the vertical axis any more. For this reason, I would suggest using an altimeter to obtain height.

Temperature is simple, is distance the measure from launch to land?

bmcculla

I guess I did forget Temperature (though if hard pressed you probably could find some way to measure it with an accelerometer :wink: ).

With a bit of filtering you probably could get ok measurements of velocity and height from the accelerometer. Another way to get a velocity measure is a upward pointing tube connected to a presure sensor (this type of sensor has a name that I cant remember right now). You could also attach a small fan to the nose of the rocket and get a good idea of speed by measuring its speed of rotation.

Brent