Hi all,
To the best of my knowledge any version of the lcnc pid is in software.
OTOH mesa does offer SOFTDMC which does run in/on mesa fpga products.
However, that breaks the core concept of multiple vendors and real ease
of user modification of the software although there are a few in this group
that could fiddle the code for an fpga. In addition softdmc needs all
the support written to wrap around it; interp, task, etc. Years ago I
head a rumor tht someone had tried to do it and abandoned the effort. If
I recall correctly it does offer something besides trap accel, controls
jerk and runs on a 50 us clock.
The manual is available online.
Dave
On 9/19/21 5:12 PM, Chris Albertson wrote:
Is the PID controller running on the PC under LCNC or is this an external
PID controller you built?
What are the numbers, the loop period, motor speed and numer of encoder
lines. and so on?
I don't think the fact that there is a worm gear matters. The problem, I
bet is the large inertia of the system.
Aside from proper tuning of the PID gains you could change the system to
use a nested or "cascade" PID. THis allows the velocity setpoint to be
controlled by the position error
see the section "cascade" in the wiki article
https://en.wikipedia.org/wiki/PID_controller
I think you want a very fast loop i=for the inner PID. LIkely it
wouldbe in external hardwarelike a microcontroller or FPGA. (does MESA do
the PID algorithm in the FPGA? It should.)
On Sun, Sep 19, 2021 at 3:39 PM Gene Heskett <ghesk...@shentel.net> wrote:
Greetings all;
As most of you know, I built a servo from scratch for a BS-1.
But I am not at all happy with its performance.
It is a motor with a worm output, driving the worm of the bs-1. And it
has an A/B quad encoder in it.
But I must rather severely limit its run speed because the PID doesn't
see the null coming near fast enough to slow it and stop a couple
arcseconds early. I can't allow it to use reverse to stop as the motor
seems to be a near short circuit then, crowbarring the power supply,
causing a 2 to 3 minute dead time for the 450 watt psu to cool, so I
must limit its speed to disallow its use of reverse to accomplish the
stop. With 2 worms in series the scale for a 360 degree full turn is of
coarse huge. If it could be throttled to a gradual stop by anticipating
the coming null, I could probably run it 2 to 4x faster for a cruising
speed.
So my question is, which of the pid inputs would if raised, better
anticipate the approaching null, slowing it over the last 5 angular
minutes of a turn, ideally to a stop within an arc-second of the command
from the gcode?
Thanks all.
Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/gene>
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