How well is backlash comp working these days?
that's a fargin' silly question! :)
(because you know that backlash is evil, regardless of compensation)
I debated asking that question for quite a while.
How you doing Steven?
That storm miss you up there?
just dug out from the 2.5 feet or so of snow
ouch. missed me completely unless you count -30f as a storm.
rayh: there were some improvements to backlash compensation for emc2.1 but I know nothing about the particulars
it was a bit higher than the snowblower, so it wasn't fun, especially at the end of the driveway
Yuck. I've had that here where the blower tries to dig a tunnel.
Thanks jeff. Guess I'll have to introduce backlash on an axis and see what happens.
yep - add to that the fact that the van gets parked in the driveway, and it becomes a real mess
our back deck looks pretty funny though - you can just barely see the thermometer, which is hung below the rail (which is at about 3.5-4' height)
I can imagine it's a mess. Had a blizard in ND which locked us in doors once.
yep. I remember those from the "old days" (the '70s, in my case)
rayh: I think it's the patch offered by "Bas Laarhoven" in this message last fall: http://sourceforge.net/mailarchive/forum.php?thread_id=30527078&forum_id=6435
rayh: now you know all I know
Crawled out the window in the door and along under the eave to the end of the apartment building.
the annoying thing is that I went out there to clear the driveway before I had any coffee, and noticed a while later that a neighbor was digging out everyone's driveways with his backhoe/bucket loader
if I had known about that' I would have had the coffee first :)
So worst case, jeff, if that is the implementation would be the need to leave a bit of accel overhead.
[19:51:54] <SWPadnos> http://www.dilbert.com/comics/dilbert/archive/images/dilbert2007916360215.gif
rayh: sounds like up to 150% of acceleration and/or velocity will be used during backlash correction, so if you are using stepgen set your headroom maximums accordingly
got it, thanks again jeff.
I'll run some tests on a slow system using sim and halscope.
good luck ray
experimentation is the key to understanding new things
Thanks. I'll report back.
I wonder how difficult it is to remove some of the larger packages from the LiveCD, and replace them with development tools (for installation)
there are runnable versions of OpenOffice apps, for instance, that probably aren't needed while using it as a LiveCD
SWPadnos_ is now known as SWPadnos
fascinating stuff in the traces with backlash
fascinating as in working?
the accel and vel are both limited during the backlash period
it just looks like there's an extra v or ^ in the axis velocity where the axis reverses direction
[21:11:42] <jepler> http://emergent.unpy.net/files/sandbox/backlash.png
from top to bottom: X position, velocity, acceleration
running part of the torture-test gcode
that looks pretty promising
the noise in the accel (second half) is strange though
yeah that sums up my throughts
If you make the backlash larger than can be accomodated during the accel period both accel and max vel are violated.
for small values of backlash compared to the accel time it looks real good.
I think the "noise" is caused by the fact that planner says "I'm getting ahead of position now."
Can we pastebin or some such images?
some folks have used imagebin.org for that
motion command was mdi x0y0 from x1y1
xvel and yvel overlap so you just see the backlash difference.
the red line.
[21:41:27] <rayh> http://imagebin.org/7312
shows velocity and accel curves for a 0.005 backlash.
Max vel is 30ipm.
accel is 5
the traces are -- motor positions and accelerations?
green and red at the top are vel
and they overlap red is x with backlash green is y with no backlash.
So we can see differences in vel caused by backlash
the light colored below is xacc
the lower blue is yacc
so the area between green and red represents the backlash distance
what shape is the G-code producing?
(circle, square ...?)
Single linear move
from x1y1 to x0y0
ok, 45 degree angle, and reversing from time to time, or just one move in one direction?
just one move in the direction that adds backlash.
that looks like a wrong algorithm
it's only the first part of the move, right?
Right. It is the start of the move only
and only up to velocity
ah - nevermind. I was looking at the red/green as position, not vel
I'm still confused, because I thought the trajectory planner had a trapezoidal velocity profile, and neither of those velocity plots is a trapezoid
the green would be if we could see the end (I think)
it's the first half of a trapezoid
it's curved, though
The green comes close to a trapezoid
jepler: the acc looks a bit traezoidal because of the cubic smoothing
Yes there seems to be some s curve ramping.
that vel is from a ddt off stepgen, or is it the output of the TP?
cradek: oh ok
stepgen does some curves of its own
I thought we set traj == servo in all the sample configs
ddt from the sim
you might get a squarer accel if you make traj = servo
jepler: not sure, but I don't think so
rove me wrong
Rove is wrong!
nevermind, I must have been thinking about abolishing a fast "base" thread in the simulator configs that don't need it
I guess I assumed that timing errors introduced by ddts would cancel out if I moved both axes at the same time and overlapped the plots.
are the two accel plots at the same vertical scale?
they seem pretty close at the end
I think so
oh - what's the INPUT_SCALE in the sim configs? 4000?
nevermind - /me is being think at the moment
thick, that is :)
INPUT_SCALE isn't important for the simulators except for servo_sim
Ah I increased input scale to 10000 so that I'd see detail a bit more
shouldn't matter, unless you're using one of the stepper configs
guess that didn't make any difference
if you're using an actual sim config, you shouldn't have anything connected to the motion controller output
I did set max vel at .5 (30 ipm)
other than a couple of ddt's :)
and max accel at 5
It does look like position is just connected to the ddts.
on a separate note, I just did some latency testing with the 2.1 liveCD on my Athlon64 machine, and I get around 10.9 uS max, when dragging windows around, starting openoffice, and browsing the CD
what video driver running?
lemme check. I'll bet it's either VESA or nv (this is a Quadro FX3500 card)
wow -it's actually nv
run two GL apps (even glxgears) and it won't work so well
no - it's about sqrt(nvidia) performance right now
I mean it will pork the latency test
406 fps for glxgears, vs 19000 or so with nvidia
lemme check that
it went from 9.7 to 11.3 uS
I even maximized one of the windows (to 1920x1200)
I'm surprised - on my machine that porks it badly
what class of CPU (and video card)?
sempron? 64 running in 32 mode, cheap nvidia card
this is a 64-bit processor at 2.2 GHz, plus a workstation PCIe video card, so maybe the relatively high raw speeds mask the problem a bit
ok, socket 754 probably. is it AGP or PCIe?
interesting. I wish I had a combo AGP/PCIe motherboard, with two video cards that are otherwise equivalent so I could test how much of a difference that makes