[SciPy-User] lsoda vs. Coulomb friction

Ryan Krauss ryanlists@gmail....
Wed Feb 10 09:57:08 CST 2010

FYI, I am moving to a slightly more sophisticated approach, similar to
Anne's third recommendation or the top of page 99 in the book Chuck
referenced.  The system is a DC motor with internal friction.
Originally, I was doing open-loop testing with a pulse input.  Now I
am putting the system under proportional control and it needs to be
possible to change directions.

So, I am going to write a case that tests for the possibility of
either sticking or changing directions.  Since the experimental
closed-loop system calculates an input that remains constant for each
fixed-width time step, I think I can handle this cleanly in a for
loop, looping over the time vector.

On Thu, Feb 4, 2010 at 10:37 AM, Charles R Harris
<charlesr.harris@gmail.com> wrote:
> On Thu, Feb 4, 2010 at 7:33 AM, Ryan Krauss <ryanlists@gmail.com> wrote:
>> Thanks for all the excellent and thoughtful responses.  I kind of
>> expected Warren to yell at me to stop using smooth solvers on
>> discontinuous systems and leave it at that.  Your responses not only
>> give me somethings to try, but make me feel like my question really
>> was a good one.
>> For now, I am basically following Anne's first suggestion:
>> * Declare that when the discontinuity becomes important, the Coulomb
>> friction model becomes too crude an approximation, and stop.
>> (Obviously if the results agree with experiment this is unnecessary.)
> That is sort of like the "switch" method in the reference I linked. That
> looks like the easiest way to go for simple systems.
> <snip>
> Chuck
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