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Topic: Self Balancing arduino robot directly controlled with a Wiimote (Read 9720 times) previous topic - next topic

Timen

Hi everybody I would like to show the project I was working on for the past six months and
also my first major project.

Its a self balancing robot that you can control with a Wiiremote, that is connected to the arduino using a bluetooth dongle and a Usb host shield.

http://www.youtube.com/watch?v=fNjMjCtNWs0

for more information go to:
http://letsmakerobots.com/node/26095


prof_jazz

congratulations..

I followed the kas guide and with his same components and pid values the bot was working fine..
I changed the IMU and cannot find the right PID values..

I read a lot of theory about PID, but...nothing stable as Your bot.

Are You using encoders? Do You use PID with angle and PD with encoders or what else?

bye,
Danilo

bill2009


CrossRoads

Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Timen

Thanks for the replies,

And Danilo yes I am using encoders it is a vital part for balancing on 1 point otherwise it will always drift.

For the PID i suggest starting with a value of 30 and working your way down until the jittering is minimal.
I use a PID for the IMU and a PD for the encoders I find the iTerm to be not that important. But the
website I can recommend to you is http://www.x-firm.com I have used that one A lot, and
it is very good in explaining all the different aspects of the code.

prof_jazz

Timen,

i am using the same code You are using (more or less Kas style)..

the theory for PID tuning says:

For manual tuning, set all three constants to zero, then turn up Kp until oscillation occurs. 
Then turn up Kd until oscillation disappears.  Adjust Kd until the system is critically damped, i.e. there's no overshoot. 

Did You follow this rule?

Could You post a video of your bot drived only from Kp (IMU) until oscillation occurs?

I would like to understand what means "oscillation occurs".

Driving my boot only with Kp this is what happens:

Kp low the bot falls;
Increasing Kp around the " error zero" it vibrates a little bit then falls.

do I have to assume that " until oscillation occurs" means this vibration around  " error zero" or an oscillation should be more "important", lets says -20 __0___+20 or -40 __0___+40 in pids?

thanks,

danilo



Timen

oscillation occurs. that means the bot keeps going back and forward and the back and forward motion does not increase. But no I did not follow that rule because I think that only works with sensors who give a physical output you can measure easily not something you can do with the movement of the balancing bot.

The way I did it was start with a Kp of 40 Ki = 1 and Kd = -8 than just lower the Kp until you think the bot balances OK it will still jitter but that is really hard to completely remove. If you found your Kp than just modify Kd until your bot does not jitter so much you will never remove the jittering because of the backlash. The Ki i found does not affect the balancing a lot. But its mainly experimenting around with values it will take time and practice but with 2 POT meters it is a whole lot easier and faster to do because you can adjust the constants on the fly.


prof_jazz

Timen,

thanks again..

I am now working on this 3 actions:

1. make the bot higher (from 30 cm to 50 cm)..4 floors instead of 3...
2. use 2 potentiometers to change Kp and Kd without compiling and uploading each time...
3. use a 4800mah li-ion instead of a 2600mah mi-nh battery...

We are using the same Pololu motors, do You think that the new battery could drive better the motors?

bye,

Danilo



Timen

#9
Apr 07, 2011, 10:21 pm Last Edit: Apr 07, 2011, 10:25 pm by Timen Reason: 1
It depends on the voltage of your battery if you use 3 cells your voltage should be 11.1 volt which is just fine.

But I do recommend removing the motor encoder code for now just make you bot balances using only PID and than look into that. All at once is just to much! And I strongly recommend using my PIDPD loop when you start with using your encoders! I could not get kas his encoder code to work so I used other code.

Oh and one last thing Keep the COG(center of gravity) as high as possible! batteries on top that means!

Ok one very last thing balancing bots are a hard thing to make but it IS SOOOOOOOOOOO rewarding when it finally stands!(so don't give up)

prof_jazz

Hi Timen,

I am following Your suggestion about using Pots to find out Kp and Kd...

Now I am facing problems on battery and motor current.

The battery I am using now is a "DC 12V 4800mAh Super Rechargeable Lithium-ion Battery" from ebay http://cgi.ebay.it/DC-12V-4800mAh-Super-Rechargeable-Lithium-ion-Battery-/120522024195?pt=LH_DefaultDomain_0&hash=item1c0fac2503

as soon as motors go back and forward all the systems shoots down and I have to power off and on again, arduino restarts..

I am using your same pololu motors and this as driver http://www.shop.robotikhardware.de/shop/catalog/product_info.php?cPath=65&products_id=112 ...

Did You ever face this kind of problems?
What kind of driver are You using (could You post a link)?
What kind of battery are You using (could You post a link)?

thanks,

danilo



Timen

Hmm it indeed looks like your motor driver or battery is the weak link. My german is very bad so I can't say if the motor driver is any good but I don't think that is the problem.

I myself used this one: http://www.sparkfun.com/products/9815

But that one was just because I did not have anything better laying around but it gets pretty hotttt:P

And the battery looks like first grade chinese crap... But I don't really know if a premium battery is necessary for this kind of usage. So I don't really know where the fault is located but you are looking in the right direction.
Maybe that low quality battery do make a difference I paid 85 euro's for the same amount of energie storage:
http://www.rctechnics.eu/hyperion-5000mah-p-3976.html

And can't you try testing your setup with a program that runs your motors at all kind of speeds and all kinds of directions.



prof_jazz

Timen,

the problem is the battery.. i get back to my old battery (a very simple pack of 10 1,2 nimh 2600mah) and the system does not switch off..anyway it still does not stay up..

Ok, the  photo "1" is my first release..it could stay up for 45 min, it hat a sonar sensor to avoid obstacles and a turning  infrared receiver to understand the direction of the ir emitter and to follow it....the main kode was based on Kas thread.

I think that some inverse current coming from the motors burned arduino, the sonar sensor and the Sparkfun 5DOF analog IMU....at that time I was using the simple pack of 10 1,2 nimh 2600mah.

The new release is based on Freeimu (from Fabio Varesano), a digital 9DOF that is working pretty fine (photo "2").
I inserted a diode on the +12v line that powers the motor driver.

The crappy battery that does not work is in the photo "3" ..I am now back on the simple pack of 10 1,2 nimh 2600mah, the system  does not switch off but i cannot reach the "until oscillation occurs" (with Kd=0)..I believe that motors are not powered enough..

I'll try to build up another pack of 10 1,2 nimh 2600mah and put the 2 pack in parallel or try to order your same Lipo battery pack...

Any idea?

BYE,

Danilo



Timen

Ok 2 things is your sensor as close to your axles as possible?

And if you put Kp = 40 Ki = 1 and Kd = 8 in you robot does it stay upright I just need to know that.

prof_jazz

yes, the sensor is close to the axis..

do You mean Kp = 40 Ki = 1 and Kd = -8 (!!-!!) ?

and what about K?

thanks

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