[Dprglist] KD01 Rotate in Place video

John Swindle swindle at compuserve.com
Tue Jan 26 00:12:53 PST 2021

The slight surge is likely due to windup. The gears were at limit when the first rotation stopped, so the second rotation would have a delay and then a jerk.
Also, the caster has to rotate, and that creates an effect that the control system might not know about.

Suggest a windup preamble in all motor commands.
I am not a mech eng, but I joined DPRG to learn relevant mechanical things, and I've learned more than I expected.
Later,John Swindle

-----Original Message-----
From: Murray Altheim via DPRGlist <dprglist at lists.dprg.org>
To: dprglist at lists.dprg.org
Sent: Mon, Jan 25, 2021 1:52 am
Subject: Re: [Dprglist] KD01 Rotate in Place video

I've just updated the KD01 Rotate-in-Place Test video on YouTube, which now
performs a bit better than the previous version: the KD01 accelerates properly
up to speed counter-clockwise, maintains that for 10 seconds, then decelerates
to a stop, then does the same thing clockwise:

  KD01 Rotate in Place Test

The position of the robot at the end of the test is about 4cm from its initial
position, which isn't too bad all things considered. There is a noticeable
surge when the robot starts again clockwise after a pause. I'm not sure what
this is caused by -- nothing in the code is indicative -- but I'm overall
happy with the result. I think it helped that I ran the test this time on
some smooth particle board.

The NZPRG Python robot code can be found at:


with the rotate-in-place test file at:


The KD01 is a differential drive robot that uses a Raspberry Pi with a
PiBorg ThunderBorg motor controller, an OSEPP drive train and hall effect
motor encoders, a tiny Adafruit Mini PiTFT 135x240 Color display that I
use as a console window, which includes two small buttons I've wired up
to initiate/control the test. The rear caster is an OSEPP wheel installed
into the frame of a commercially-available caster.



On 23/01/21 4:04 pm, Murray Altheim via DPRGlist wrote:
> Sometimes it's important to prove one is making progress. Not that this is
> advancing the science at all but I've just posted a video showing the KD01
> differential drive robot rotating in place using its PID controllers: [...]
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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