[Dprglist] Assisting PID odometry with an IMU

[Murray Altheim]

On 23/01/21 5:27 pm, David Anderson via DPRGlist wrote:
> Murray,
> 
> Your PID controller should handle this.   No IMU required.  It sounds
> like the PID is not responding quickly enough when it first engages 
> the carpet.   Try kicking up the gains, or maybe just the D gain.

Hi David,

Hmm. I'd thought the tuning was okay in the sense that it seemed to
perform most of the time pretty well, with that bump onto the rug is
quite a steep one (from the wood floor it's a sudden 17-18mm jump for
a 70mm wheel).

As I've now got an RGB Potentiometer Breakout and a supporting Python
class on the robot it's relatively trivial to add a knob control to
the PID configuration:

   https://shop.pimoroni.com/products/rgb-potentiometer-breakout
   https://github.com/ifurusato/ros/blob/master/lib/ioe_pot.py

In looking at my PID configuration it looks like I'm only using P and D
right now:

     kp:  0.09500
     ki:  0.00000
     kd:  0.00030

I'll certainly try some knob-tweaking to see how that makes a difference.

> From the circling in place video (bravo!) I think I see the robot's 
> wheels speeding up and slowing down,  like the controller is pumping
> or oscillating, rather than settling into a constant velocity. Seems
> like you still may need some PID adjustments.
I think I see what you mean, almost like the wheels are surging. I'll
try the test a few more times and also let it run at full speed for a
lot longer, then check the resulting logs to see if that's actually
happening or just some artifact of the video.

Thank you!

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