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Topic: Guide to gyro and accelerometer with Arduino including Kalman filtering (Read 326349 times) previous topic - next topic

bilbo-bongo

yes sorry i meant z-axis.

ok, i'll try research into that. Or else i might be able to get an arduino mega.

Worst case scenario i can still work with the values i am getting

Lauszus

Okay. Please upload the code for calculating the angle with only two values from the accelerometer when you get it working :)
- Lauszus

Lauszus

I thought a bit about it, and actually you can calculate the axis with just one value.

In the code it says:
Code: [Select]

accXangle = acos(accXval/R)*RAD_TO_DEG-90;
accYangle = acos(accYval/R)*RAD_TO_DEG-90;


Instead you could write:
Code: [Select]

accXangle = asin(accXval)*RAD_TO_DEG;
accYangle = asin(accYval)*RAD_TO_DEG;

Then you should get an angle very close to the first one!! It is not as precise as the first one, but that kind of precision is only important if you are building a balancing robot or something like that.
The resolution will also only be 180 degrees.

That should fix your problem :)

- Lauszus  

onidaito

Guys, I really think I should be getting better yaw values from the Gyro. I found this:

http://code.google.com/p/imumargalgorithm30042010sohm/

This shows some pretty decent output which leads me to believe that my unit could be broken as the Yaw value doesn't change at all when I rotate around that axis. I noticed that on the sparkfun page for this item, someone else had a similar problem. I've emailed the chap from the link above in the hopes that I can figure this out. At the moment, the lack of decent/any yaw (no need to use a magnometer just yet) is halting my project :( Im wondering if there is something else im missing here. I've tried the kalman filter approach as well and that seems worse than just using the raw gyro values :S

Lauszus

You can not use the kalman filter for the yaw value, because the accelerometer can not measure the yaw :)
Hope you get it working!
- Lauszus

onidaito

Yeah, I've done a little more research and I see what you mean. I guess i just need to integrate over time for yaw off the gyro and then reset when the drift gets too much... until maybe I get a magnetometer as well!

Thanks though! Its been a big help!

corez

Hey guys,

Is it possible to also use the kalman filter for only an accelerometer? It will only use one axis (of the three available). I just need a smooth movement of the servo I'm using

Lauszus

You can not use the kalman filter with only one input. Sorry but you need a gyro too, that is why it called "sensor fusion" :)
You could perhaps use some other kind of smoothing algorithm.
- Lauszus

bilbo-bongo

Hey Lauszus, I finished my final year project in college. I thought I would show it on here so people can see what can be done with the code and sensor. Thanks again for you help!



http://www.youtube.com/watch?v=pg3q3MTSL5g


Lauszus

It look and sounds very cool. Thanks for sharing. So which academic degree do have now?
- Lauszus


corez


You can not use the kalman filter with only one input. Sorry but you need a gyro too, that is why it called "sensor fusion" :)
You could perhaps use some other kind of smoothing algorithm.
- Lauszus


Any recommendations? I found these...

http://arduino.cc/en/Tutorial/Smoothing

http://www.arduino.cc/playground/Main/Smooth

Don't know how smooth they work, didn't get time to test them yet

Lauszus

I haven't got any experience myself, but it look likes what you need :)
Or you could just write something like this:

Code: [Select]

int difference = reading - lastreading;
abs(difference);
if(difference > 10) reading = lastreading;


It will ignore the data if you for example shake the sensor.

The best solution might be combining those two approaches.

- Lauszus

beltran

Hey Lauszus
thanks for providing this great guide!!

I've read your comments to onidaito and I'm not exactly sure of what you mean when you are saying that
Quote
the accelerometer can not measure the yaw


I'm trying to understand if for my project I need 6 or 9 degrees of freedom
So let's be straight and have a visual example:



can the sensor you are using (and the code) measure all these 6 variables?
thanks in advance
b.

Lauszus

The accelerometer can measure the roll and the pitch, but not the yaw. The gyro can measure both the roll, pitch, and the yaw, but all these will drift. In total that gives only the roll and the pitch. You need a magnetometer to measure the yaw too.
- Lauszus

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