Angle measurement for balancing robot.

[vacpress]

joe - this was my first reaction also. but then i read this N&V article... they put the batteries in the 'head'... and consider the segway... sure the batteries are in the base, but the center of gravity probably is closer to our mid section when it is being ridden...

i get the impression that a high center of gravity is important.. i also notice that most bots put the accelerometer low, near the wheel axle height...

if anyone has more info.. i am reading along.. interested in the concepts, if not actually making my own balancing robot!

i know it may sound like sacrilege, but try the parallax forums.. very helpful people there...

[mister_e]

It's 2007, resource are everywhere and mostely free... so what's the problem to look elsewhere, i don't see any. This is why divorces exist after all

In this case it's more about problem approach and/or problem analysis than anything else. Time to dig in you old school books or take a few cup of coffee to see what's happen

[Archangel]

joe - this was my first reaction also. but then i read this N&V article... they put the batteries in the 'head'

I will take the time to read that article again.
JS
Edit:
The article says they moved the batteries up to "increase the inertia", I see that as an attempt to cause the accelerometers to respond faster. Their robot chassis is made of whiteboard, probably the reason they needed to increase the inertia, as that cardboard is not very stiff, I believe they could have achieved similar results by moving the accelerometers up to the "Head"
where nature put ours. Anyway those are my thoughts on the matter, It's up to you to sort out whats good and what's useless.
Have fun,
JS

[HenrikOlsson]

Hi Joe et all,

Try this: Take a pencil (low inertia) and try to balance it on the tip of your finger. Not really that easy is it? Now take a 1m (3foot) stick (more inertia) and try again, easier...?

Even better, take a pool que, try to balance it with the "fat" end down (batteries mountes low), then turn it around (batteries mounted high), which is easiest?

/Henrik Olsson.

[Archangel]

Because you are moving the part with the lower mass

[Ioannis]

That's right. It is easier to adjust something with lower mass than the Lead-Acid Batteries!

Also putting the accelerator sensors down, produces less spastic movements of the motors. Inertia of the highest parts takes care of the rest.

It is a very impresive project and needs good close loop control design. Although I don't know if it worths it since the energy to accomplish that is way to high.

But, on the other hand, for the wow's that the designer is going to accept, may be it is worth it!

Ioannis

[uffi]

Hi Henrik,

thanks for the file and the link. I downloaded all the stuff from the nuts 'n volts FTP server. Obviously these guys creating B-Bot have adapted some code originally developed for the helicopter autopilot on sourceforge. Thank you again.

Regarding my implementation: no, I am working on a C-code implementation for the ATMEGA16 to be compiled with win-avr or gcc, resp.

When you adapt my formulas for the tilt angle from accelerometer data, please care for the fact, that the accelerometers have different sign for dynamic and static acceleration. This fact is not yet considered in my formulas. So the sign of "a" must be inverted for the real measurements.

Have you done any work on implementing my formulas?

Kind regards, uffi.

[HenrikOlsson]

Hi Uffi,

Regarding my implementation: no, I am working on a C-code implementation for the ATMEGA16 to be compiled with win-avr or gcc, resp.

Oh crap, yet another C implementation....and not even for PIC... ;-) I've started to look at C for PIC's but that's not a topic for this forum.

Yes, the Kalman code comes from the UAV project. I have not had time to work on implementing your formulas yet but thanks for the pointer on the sign of the acceleromter readings. I'm not sure the accelerometer formulas will work with the sensor I got now. It is a two axis accelerometer, X and Y but I'm not sure how it will respond if mounted so it "becomes" X & Z. I will have to experiment with that too.

I got the SHARP sensors yesterday and managed to get the robot balancing fairly well. It's still a little "nervous" but I think I'll get it better by filtering the readings and/or experimenting with the sensors mounting. The goal, however, is the acceleromter/gyro aproach since the SHARP sensors introduce too many drawbacks IMO. But hey, atleast it works!

Thanks!
/Henrik Olsson.