Re: [Emc-developers] pid with derivative inputs

[Chris R. <ch...@ti...>]

On Mon, Nov 01, 2010 at 12:13:36AM -0500, Jon Elson wrote:

> One quirk, which I think is inherent in the way that HAL component 
> encoder.c works,
> and which I copied,
> is that a dithering encoder gets the wrong velocity.  

When Seb K was working on the hostmot2 driver, one of the kinds of
wrongness we found (and he fixed) was

http://timeguy.com/cradek-files/emc/encoder-velocity.png

This plot was from a real machine with minor dithering at very low
speed.  I do not think the software encoder component is quite right
near zero speed.  I think Seb started with that code and improved it
to get the good results we have from hostmot2 now.  You might want to
browse the git history to see what he did?

The changes 84e73cbd534 and especially fed9d8e5a58 look relevant.

Chris