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Topic: PID parameters for self-balancing motorcycle (Read 215 times) previous topic - next topic

glenz

I would like to hear about the experiences of some other members regarding tuning the PID controller of the motorcycle.   I have had very little success  after several weeks of attempts to get the motorcycle to stay upright for more than 20 seconds.  I have the 6V motor, if that is significant. I have been "playing" with the parameters Kp, Kd, gain, and bias. The inertia wheel will never do more than one "zero crossing" before falling.
Even when it is temporarily  upright the slightest puff of wind will send it into instability from which it cannot recover. There is one video on You Tube which shows the motorcycle in stable motion but he/she does not respond to my enquiries. I have had some experience in writing/tuning PIDs in the context of straight line travel of wheeled robots so I am not totally naive. (I wish the inertia wheel was a laterally directed propellor)
My most successful parameter values are Kp = 80, Kd = 10, gain = 0.1, bias = 0.87
Am I the only one having this problem?

Ajaj

From my initial testing the bike has a number of problem making it not so stable. You can achieve some stability but it's not very robust.
First the motor max torque is low compared to the vehicule it should keep upright so it will easily saturate the controler.
Second it has to be very well balanced or "biased" or the wheel will quickly pick up speed and stop generating torque.

A motor with a bigger Torque constant would help, also a the algorithm should include dynamic bias to compensate for equilibrum offset and also speed compensation to to alleviate back EMF effect.
It would be more robust this way.

gzwicker

Hi Ajaj,
  Thanks for responding.  Your comments mirror my thoughts exactly. Without dynamic bias adjustment gravity will win every time because it is relentless while the supply of (counter-torque x time) that can be supplied by the inertial wheel is very limited.
   Today I added a Ki branch to the controller circuitry and after some tuning was able to get the bike to stay upright indefinitely. I pushed it over, with a very slight force, after about five minutes because the motor was getting pretty hot. I can give you details on this mod if you are interested.
 

Ajaj

Yes i'm interested by your tuning, it(s always time consuming to go from concept to prototype that work. I'll try to add all mods i have in my mind at some point but i have a lot of teaching material to sort first. A ki on bias with small gain looks to be the way to go first.

gzwicker

I'm using Kp = 90, Kd = 10,  Ki = 0.8, and master gain = 0.1.  As an integrator I  used the "DiscreteIntegrator" block with its limits set at +/- 50 and its other settings at default.  The limits prevent a large build-up of correction while the bike is still on the kickstand. Alternatively I suppose one could put a gate inline with the integrator controlled by the Fallen signal.

gzwicker

Apparently my successful trial of yesterday was a fluke as I am not able to reproduce it today : (

gzwicker

I also got some encouraging results with Kp = 45, Kd = 4, Ki = 1.9, gain = 0.1.    However, not being able to get consistent satisfactory results I am going to give up the project temporarily and go on to the Mobile Rover. Perhaps in the meantime there will be some helpful discussion about the self-balancing(?) robot here as others try that project.

MadhuGovindarajan

The motorcycle's best balancing in the current format is about 45 seconds to 1 minute. For longer than that you have to dynamically tune the motorcycle over WiFi which is beyond the scope of the online learning materials.

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