[Dprglist] Assisting PID odometry with an IMU

[markus]

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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