[Dprglist] Assisting PID odometry with an IMU

[markus]

what I forgot - you tune them independently, L/R first so the motors
follow their set value correctly under load - and then A to your
steering requirements.


On Sat, 23 Jan 2021 15:32:39 -0800
markus via DPRGlist <dprglist at lists.dprg.org> wrote:

> Hi Murray,
> 
> I'm not sure about your architecture, so this might be redundant. Many
> years ago we had a similar discussion here and as a result I
> implemented 3 PIDs for my differential steered robot.
> 
> One PID (A) does the steering and determines the set points for each
> motor. And those are used as the input values for two PIDs (L and R),
> one for each motor. L and R use the same configuration and ensure that
> each motor actually does what is expected of it, without impacting the
> other motor. Note that L and R should run faster than A. I have A
> running at 100Hz and L/R running at 1kHz - I chose 10x more or less
> arbitrary.
> 
> Have fun,
> Markus
> 
> 
> On Sun, 24 Jan 2021 11:41:33 +1300
> Murray Altheim via DPRGlist <dprglist at lists.dprg.org> wrote:
> 
> > On 24/01/21 2:57 am, Carl Ott wrote:> Hi Murray,  
> > > 
> > > regarding PID tuning of your heading loop -
> > > 
> > > have you tried to examine the heading loop step response?
> > > 
> > > For example - what happens if you place your robot on that
> > > turntable at your desk -[...]    
> > 
> > Hi Carl,
> > 
> > I've seen several YouTube videos of people running robots over
> > rotating turntables, with their finely-tuned robots surmounting the
> > turntable, running across it, exiting onto stable ground and
> > reaching the target at the other side. Very impressive.
> > 
> > I'm nowhere near there yet, though it occurs to me that this would
> > be a *great* challenge for club events if someone were willing to
> > build such a turntable, of a "standard" size (we'd have to develop a
> > standard, maybe a smaller one for Zumos too). I'd think one full
> > sheet of plywood with a circle cut in the middle, mounted on a
> > turntable, with a line drawn along the longest axis. The robot that
> > can go from beginning to end across the turntable at the highest
> > velocity wins. Or something like that.
> > 
> > So far I've only used my robot test bench turntable for IMU testing.
> > As the wheels are off the ground the PID tests aren't so helpful --
> > one can get a start on the configuration but it seems the tests need
> > to be done while actually driving the robot over ground.
> > 
> > I was pointing out to David offline that as different from his
> > RCAT's (I believe) 4 inch wheels, the OSEPP wheels on my KD01 are
> > 70mm (2.75") -- about half that size -- and the bump on the rug is
> > 17mm, which is about half of the wheel radius.
> > 
> >    https://service.robots.org.nz/wiki/Wiki.jsp?page=PIDRugBumpChallenge
> > 
> > By comparison, the RCAT would have to manage a rug bump of about
> > 1.25-1.5 inches without being deterred from its path.
> > 
> > Another simpler club challenge might be to effectively create a test
> > course with a line down the middle and rug on one half, so that the
> > robots need to confront that rug and still PID their way down to the
> > finish line. Pretty basic but clearly a challenge for us beginners.
> > 
> > My KR01 robot uses the same wheels but is 4WD and weighs about twice
> > that of the KD01, so it's not affected anywhere near the same by the
> > bump. Also, being "non-differential" it resists forced rotation
> > around its axis when one wheel hits an obstacle, unlike a
> > differential drive robot.
> > 
> > So one has to be *reasonable* in one's expectations... but as I said
> > to David I can certainly tune my PID to better handle such
> > obstacles. I don't think he'd mind me quoting him:
> > 
> >     "Even at very low torque/low speed the robot rotates through
> > maybe a degree before mounting the carpets, and then once mounted
> > the PID controller over-corrects and that straightens it out onto
> > the original path. So a little figure 'S'. At higher speeds it just
> >      goes straight over the elevated carpet, with no change in the
> > path."
> > 
> > So that's kinda my goal now. I might use a lower bump (different
> > rug) than the
> > 
> > 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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