[Dprglist] PID

[Murray Altheim]

Hi Patrick,

I wasn't aware of the term, but one of the things I remember David
Anderson saying in his YouTube video, amplified by some other things
I'd read/seen, was that tuning the PID and developing the robot's
behaviours essentially sets up its observable personality. And being
a child of aesthetics (i.e., background in the arts) I want my robot
to exhibit smooth moves rather than appear jerky (so uncool). So
once I've got to the point where I can reliably control it I'll be
interested in exploring this idea of motion profiling.

Thanks for that.

Cheers,

Murray

On 30/09/20 7:11 pm, Patrick R. Michaud wrote:
> This reminds me of what I've seen called "motion profiling" in FTC/FRC, where the motors (driving wheels) use PID to follow a velocity curve rather than a position setpoint.  The end result is a lot smoother stop/start of the motors, since a new position setpoint doesn't result in a drastic step change in the P-term going to the motors.
> 
> The navigation library (Roadrunner) my team used in last season's competition used velocity motion profiling for its drivetrain, and it was really nice to not have sudden starts/stops impacting the autonomous navigation.  They also wanted to try to do some motion profiling on their lift mechanism, but didn't quite get that working (they were able to tune a simpler PID to be "good enough").
> 
> Pm
> 
> On Wed, Sep 30, 2020 at 02:00:29PM +1300, Murray Altheim via DPRGlist wrote:
>> Hi Rud,
>>
>> The setpoint for the PID controllers is a velocity value. The basic
>> task is to accelerate to cruising velocity at 25% of the distance,
>> then slow at 90% down to targeting velocity to stop at 2m.
>>
>>    0                              1m                             2m
>>    0          ->cruising                             ->targeting  0
>>    0              25              50             75         90  100
>>    |_______________|_______________|______________|__________|____|
>>
>> Does that make any more sense?
>>
>> Cheers,
>>
>> Murray
>>
>> On 30/09/20 1:50 pm, Rud Merriam via DPRGlist wrote:
>>> Hi,
>>>
>>> I'm not understanding the log outputs.
>>>
>>> At line 9740 the stbd motor has reached the 2m mark. The setpoint is set to 10.00 while earlier it was set to 50.00. I would think the setpoint should be the end position, i.e. 2m equivalent.
>>>
>>> At line 9754 setpoint is not 0 and the error is 10.019. If it is at the end position the error should be 0. After that error is non-zero so outputs are generated which move the motors.
>>>
>>> IMO the setpoint should be the number of steps (or equivalent) you want the motor to have moved. The error is the difference.
>>>
>>>
>>> -73 -
>>> *Rud Merriam K5RUD*
>>> /Mystic Lake Software/ <http://mysticlakesoftware.com/>
>>>
>>> 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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>>
>> -- 
>>
>> ...........................................................................
>> 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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> 

-- 

...........................................................................
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