docs -add writeup about a dual PID axis example

[c-morley]

An example of dual PID axes in HAL

[grandixximo]

svg fails to render on github, is it hand written?

[c-morley]

no, exported from Dia program

[grandixximo]

It does not look like an svg, is it encrypted or something? I opened with text editor and it does not look like any svg I have ever seen before...

[grandixximo]

it is a PNG actually, I change the format, and now it opens up

the SVG file has the same sha256 as the PNG file, so they are byte identical, they only differ in the file extension.

[c-morley]

Ok thanks I think this fixes it.

[grandixximo]

I don't understand how summing the PID results in the position you want to sent the motor at.
You are running this on a machine?

[c-morley]

I am not, other are.
https://forum.linuxcnc.org/10-advanced-configuration/37353-dual-pid-loops-and-appropriate-pins-for-feedback-to-the-trajectory-planner-et-al

[grandixximo]

My bad, I missed the fact that it is controlling the servo in velocity mode, makes more sense now, forum feedback looks good...

[BsAtHome]

Why is there both the SVG and PNG image attached?

We should only need the SVG. Or?

[c-morley]

Yes I could delete the png.