Angle measurement for balancing robot.

[HenrikOlsson]

Hi,
I'd say +/-45 degrees from "down" will be more than enough. The problem, again, is that it needs (I'd like it) to be an absolute value in reference to gravity.

/Henrik Olsson.

[uffi]

Henrik,

during the last weekend I had a breakthrough using the kalman filter code you provided here from the nuts&volts article. I got my robot balancing based on combined gyro and accelerometer approach. Up to now I also used only one axis of my 2-axis accelerometer (therefore containing also an error due to the measurement of the robots acceleration itself: this error seems to be filtered away by the kalman code). The regulation is only PD-control, not PID, but I plan to extend it to PID to get better control of absolute position. I have a demonstration video (6MB) which is too large to be uploaded here. If you send me your email address, I will mail it to you.

All approaches based on using only the accelerometer or the gyro were not successful so far: the pure accelerometer approach has a too noisy signal to be used for this kind of control and for the pure gyro approach I was not yet able to really compensate for the drift only by software.

Have fun, Dirk.

[HenrikOlsson]

Hi Dirk,
That's absolutely great!
I haven't had time to work on mine for a while. I did get it to balance fairly well using the SHARP sensors though but nothing have been done to it since then.

So based on your experience (and mine, so far) I think that we can rule out using just an acceleromter or gyro. I kind of had that feeling from the begining but was I would be glad to be proven wrong.

Now, if we only could port that filter code to PBP. Hmmm...I wonder if there's a way to compile just the filter code and use the assembler code from within PBP.

Thanks for the update, I appreciate it!

/Henrik Olsson.

[Darrel Taylor]

Hi Henrik,

Just wondering if you used your new PID "Code Example" on the Balancing Robot?
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[HenrikOlsson]

Hi Darrel,
Yes I did. The robot was the reason I wrote it. It a 18F2431 for each wheel running a PID compensated velocity servo at 1220Hz thanks to your interrupt routine. The main CPU runs the PID for the actual balancing at 100Hz.

Any chance you see some way to improove it?

/Henrik Olsson.

[Darrel Taylor]

>> Any chance you see some way to improove it?

Actually, yeah, I've got a couple ideas. I'll post them in the other thread.

But, back to the Balancing Act.
Did you use it in place of the Kalman filter, or with it?

Just curious.

[HenrikOlsson]

Hi Darrel,
Nope, the Kalman filter (if I ever understand/get that to work) would be used only to track the absolute angle of the robot platform. (Basicly removing the gyro drift). The error (desired angle - actual angle) is then fed to the PID-filter which in turn tells the motor-driver how fast the wheels needs to spin to keep it upright (or whatever).

As it stands at the moment (with the SHARP sensors) it just subtract the front sensor reading from the rear sensor reading and sends that value the PID-filter.

Thanks

/Henrik Olsson.

[uffi]

For those of you interested, I put here the link to my internet homepage, where you can find videos and description of my two-wheel balancing robot named ARTIST.

http://home.arcor.de/uffmann/ARTIST.htm

Have fun, Dirk.

[bbarney]

don't know if this is the answer but check it out
http://www.austriamicrosystems.com/0...ons_AS5043.htm