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Lowpass compass filter and highpass gyro filter 
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Joined: Sat Jul 04, 2009 7:00 am
Posts: 16
Post Lowpass compass filter and highpass gyro filter
Hi there !

I would like to implement gyro and compass combination to compute the angle of my nxt. The filters I want to work on those 2 hightechnic sensors are given here : http://geology.heroy.smu.edu/~dpa-www/r ... ertial.pdf

Has anybody already built such a code ? What kind of numeric filter would be optimized for nxt on robotc ?

Tx :)


Sat Jul 04, 2009 7:49 am
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Joined: Fri Nov 09, 2007 4:51 am
Posts: 121
Location: Hungary, Europe
Post Re: Lowpass compass filter and highpass gyro filter
Hi,

This link was posted by scb in the NXT Segway topic you can find below.

http://scb.netsons.org/files/robotcBR.zip

For the lowpass filter of the compass sensor: my proposal is an "intelligent" filter that takes into consideration the physical properties of the NXT robot. The filter shall maintain an internal state that represents the robot's angular momentum, maybe even a second internal state value for the angular acceleration.

You will have two sources for the robot's angular position:
1. you can make a calculation, based on the internal state values and the control outputs your program sent to the motors
2. you have a measured value from the compass sensor.

Before processing the compass sensor value, you can check if the measurement is within a "credibility range." If it was not, you shall throw away the measured value. If it was creadible, you can achieve the next estimation of the robot's angular position (and the internal state values) by a weighted average of the measured and the calculated values.

Such a combination of measured and calculated values are frequently used in automotive industry. E.g. the ABS/ARS follows wheel rotation and maintains an estimated speed of the car. Should a wheel's rotation abruptly change it is considered as a slip that initiates ABS/ARS intervention.

Sophisticated navigation systems achieve an exact position of the car even when GPS reception is weak (e.g. high buildings, tunnels, underground garage etc). They combine GPS signal with acceleration and gyro sensor signals (and also wheel rotation signals).


Sat Jul 04, 2009 10:20 am
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Posts: 16
Post Re: Lowpass compass filter and highpass gyro filter
Hi elemes,

thank you very much for your answer. Well I'm actually looking for real filtering rather than a tricky code. My goal is to implement the same filtering process as described in the pdf (cf my previous post) with hitechnic gyro and compass sensors. But if you had any suggestion about compass and gyro integration please tell me :)

Best regards


Mon Jul 06, 2009 10:32 am
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Joined: Sat Jul 04, 2009 7:00 am
Posts: 16
Post Re: Lowpass compass filter and highpass gyro filter
So I went on my investigations and decided to implement 2 FIR filters. I would like to compute the coefficient with matlab but I don't know if the gyro and compass are compatible with it. Any idea ?


Tue Jul 07, 2009 3:38 pm
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