[Dprglist] Assisting PID odometry with an IMU

Murray Altheim murray18 at altheim.com
Sat Jan 23 14:41:33 PST 2021

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.


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

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



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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