What do you mean? Will you just keep calibratrating all the time, to compensate for drift?
- Lauszus
hey Lauszus,
I got my sensor (nice and fast too,thanks for the germany tip!)
I have it all connected and it seems to be working. One thing i notice though is that tilting forward on the y-axis gives me values up to 60 but backwards on the y-axis i only get as high as 20. on the x-axis then i an even 40 on each side.
I notice you wrote to add in a piece of code to make it read full 360, is that why mine isn't reading right?
i tried putting in that code after
" R = sqrt(pow(accXval,2)+pow(accYval,2)+pow(accZval,2));//the force vector
accXangle = acos(accXval/R)*RAD_TO_DEG-90;
accYangle = acos(accYval/R)*RAD_TO_DEG-90;"
But didnt change anything.
also i'm not connecting the z-axis because i don't need it. I assumed it wouldnt make a difference.
Just wanted to say thanks again for the code. Looks like my project will become what i dreamed 
I'll post a video up here when its done
Glad I could help. Have you connected the accelerometers z-value? If not that is why you data is getting weird. Remember that the code uses the z-value from the accelerometer to calculate the force vector.
Looking forward to see your project in action
- Lauszus
no i didn't plug it in because i didnt need to measure the x-axis.
I am using a pressure sensor also, and using an arduino Uno so only have 6 inputs :~
so it needs to be used for calculation even if you dont plan on printing the value?
Don't you mean the z-axis (yaw)? You need it for my code, but yes it it possible to calculate the angle with just one two values I think, haven't really researched on that, because it hasn't been a problem to me.
- Lauszus
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
Okay. Please upload the code for calculating the angle with only two values from the accelerometer when you get it working
- Lauszus
I thought a bit about it, and actually you can calculate the axis with just one value.
In the code it says:
accXangle = acos(accXval/R)*RAD_TO_DEG-90;
accYangle = acos(accYval/R)*RAD_TO_DEG-90;
Instead you could write:
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
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
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
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!
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
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
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!
It look and sounds very cool. Thanks for sharing. So which academic degree do have now?
- Lauszus
multimedia
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
Any recommendations? I found these...
http://www.arduino.cc/playground/Main/Smooth
Don't know how smooth they work, didn't get time to test them yet
I haven't got any experience myself, but it look likes what you need
Or you could just write something like this:
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
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
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.
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