[Dprglist] PID

[David Anderson]

Hi Murray,

I've plotted some of your data.  Here's the error, P, setpoint and 
output for your port motor:

http://www.geology.smu.edu/dpa-www/robo/data/murray-01.png

I honestly can't make any sense of it at all.  It does not look like a 
plot from a PID controller.

The oscillations around the set point you describe are clearly obvious.  
Here's a zoom in on just that portion:

http://www.geology.smu.edu/dpa-www/robo/data/murray-02.png

It  looks like the set point, the blue trace, is moving around, not 
steady at 0.  So if the PID controller is being commanded to do that 
it's not its fault if it's oscillating.  Why is that value moving around?

The initial startup is also bit bizarre.  Here's a zoom in on that:

http://www.geology.smu.edu/dpa-www/robo/data/murray-03.png

It looks like the P,I,D terms are logged after they are already scaled 
by their gain constants.  What you need to see are the raw values 
calculated for the proportional error, the derivative error, and the 
integral, and the final output power to the motors.

Here are similar plots for your right wheel:

http://www.geology.smu.edu/dpa-www/robo/data/murray-04.png

http://www.geology.smu.edu/dpa-www/robo/data/murray-05.png

http://www.geology.smu.edu/dpa-www/robo/data/murray-06.png

It would be very useful to also log the wheel velocities.

And a time stamp.

cheers,

David




On 9/29/20 7:24 PM, Murray Altheim via DPRGlist wrote:
> Hi,
>
> Addressing the hunting behaviour on the KR01 robot that we've discussed
> previously (i.e., rocking back and forth about 1/8 of a wheel turn after
> stopping), here's a full color (!) log of the journey:
>
> https://service.robots.org.nz/wiki/attach/PIDController/pid_bounce_log.html
>
> I may mention this in tonight's video discussion, thought to provide a 
> link
> here. It basically shows the encoder and PID controller output as the 
> robot
> accelerates to cruising speed then decelerates to a slow, targeting 
> velocity
> before attempting to stop at the 2 meter mark.
>
> Cheers,
>
> Murray
>
> ........................................................................... 
>
> Murray Altheim <murray18 at altheim dot com>                       = 
> =  ===
> http://www.altheim.com/murray/ ===  ===
> = =  ===
>     In the evening
>     The rice leaves in the garden
>     Rustle in the autumn wind
>     That blows through my reed hut.
>            -- Minamoto no Tsunenobu
>
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