Kinematics and Delta Robot

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10 May 2019 04:43 #133322 by Sockheaven
Ahh you're right.
Once I changed the axis limits so that the starting Z value was within the limits, i was able to jog the Z axis. Thanks!
I think there may be a bug in there because when X and Y start out of bounds, an error popped up to let me know i was in a software limit situation, but that doesn't happen with the Z axis, it just silently fails when you try to jog.

I think i'm ready to set the current limits low and try on hardware and see what else I've configured wrong :-)

I am still unsure what precisely the rotarydeltakins is doing with respect to homing. the start Z axis position makes me think I don't know precisely what angle the hips think "0 degrees" means for the joint.

Hopefully running on the real mechanics will be more enlightening to what the kinematics are expecting for the origin.
Will report back, thanks!

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05 Jun 2019 16:24 #135956 by Sockheaven
Thank you all for your help. You guys were an immense help.
Had some distractions keeping me from this. but spent some more time and was able to get it all working.
I even played with FreeCAD and the DXF to GCode converter for LinuxCNC to make a sample 1" circle.
11 second video: https://photos.app.goo.gl/jvZbWctHABSjzXmN9

Looks like its time to get a high power laser!

General Question - about generating paths.
I found the page on the website with tools for CAD/DXF/GCODE generation. I've never done any of that before.
I mentioned before i just took a stab at FreeCAD.

What is everyone else using?
I don't want to spend too much time learning a poor software package, but it may not be worth it for me to invest in an expensive software toolset either.

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05 Jun 2019 20:34 #135973 by andypugh
Replied by andypugh on topic Kinematics and Delta Robot

Sockheaven wrote: What is everyone else using?.


I would like to use Open Source but find myself using Fusion360. (which does at least run natively on my Mac)

Does your delta do 3 axes of 5?

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19 Jun 2019 15:35 #137292 by Sockheaven
My delta is currently just 3 axis, nothing too special.

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13 Feb 2020 13:41 - 14 Feb 2020 09:31 #157285 by barisduzenli
Hello everybody,

We are trying to realize rotary delta robot too. Previously, we can achieved wiring of 7i77 and Delta 750W ASDA-A2 servos by your helps. And currently our system can achieve trivial kinematics.

We are using V2.8 LinuxCNC with Base Thread Max Jitter 459500ns, Servo Thread 2934439ns. These are very high I dont know why. We are using AMD AthlonX2 5200+ processor with 2 gb DDR2 Ram. This is one of our problems.

To realize Rotary Delta Kinematics, we changed
[KINS]
JOINTS = 3
KINEMATICS = rotarydeltakins (was TRIVKINS)

After, in hal file we add link dimentions as below

setp rotarydeltakins.platformradius 250.0
setp rotarydeltakins.thighlength 400.0
setp rotarydeltakins.shinlength 1000.0
setp rotarydeltakins.footradius 50.0

Home is X=0 Y=0 Z=1028 calculated by rotarydeltakins (We do not changed it)

in ini file PID parameters as below (in trivial kinemation this parameters were quite good)
P=60
I=0
D=0
FF0=0
FF1=0.0003
FF2=5e-05
Bias=0
Deadband=0.000015

Finally, to specify gear ratio (from encoder pulses to reducer output, *not sure but as I understand from documents)
responsible parameters are Encoder Scale and Output Scale 360 (To illustrate 360 degree is equal to 1048576(2^20bit) pulses of encoder *not sure but as I understand from documents)

But servos turning more than a one turn (even a lot of turns) This is another serious problem to us.
Basicly, we can not specify gear ratio.

We feel very near to success but we can not reach for 3 days

You can find our .ini and .hal files.

Thank you for your helps.

File Attachment:

File Name: 1302DeltaHALINI.ini
File Size:3 KB

File Attachment:

File Name: 1302DeltaHALINI.hal
File Size:9 KB
Attachments:
Last edit: 14 Feb 2020 09:31 by barisduzenli.

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20 Feb 2020 10:51 #157976 by barisduzenli
Hello everyone,

I updated to my computer system to AMD Phenom 945 Black edition + 16gb DDR3 1600Mhz and 7200 rpm Hard Disk Drive. It look jitter problem is solved. Now, Servo Thread Max Jitter is aroud 310000 and Base Thread Max jitter is around 500000.

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20 Feb 2020 13:48 #157999 by tommylight

barisduzenli wrote: Now, Servo Thread Max Jitter is aroud 310000 and Base Thread Max jitter is around 500000.

That is terrible ofr such a system. Did you disable everything pertaining to power saving, speedstep, hyperthreading, serial ports, modem, mainboard wifi if it has one, etc.
Should be able to get much better latency.

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20 Feb 2020 16:02 - 20 Feb 2020 16:02 #158018 by barisduzenli
Hello Tommy,

Yes I am using a PCI Wifi Adapter. I plug out it and I am scaned bios settings I closed almost everything except usb and Lan adapter.

And YES :) . I get Servo Thread Max Jitter is aroud 38800 and Base Thread Max jitter is around 42700.
Last edit: 20 Feb 2020 16:02 by barisduzenli.
The following user(s) said Thank You: tommylight

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20 Feb 2020 16:28 #158024 by Sockheaven
For multicore machines I have found big benefits in isolating the last cpu core for realtime events.
Look into ISOLCPUS for the realtime kernel.

at the command line run:
$ sudo nano /etc/default/grub

Find the line GRUB_CMDLINE_LINUX="" and update it to:
GRUB_CMDLINE_LINUX="isolcpus=1" (where 1 is the highest CPU core, dual core = 1, quad core = 3, etc)

then run:
$ sudo update-grub

and reboot, your RT jitter times should decrease
The following user(s) said Thank You: barisduzenli

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20 Feb 2020 18:25 #158040 by tommylight

barisduzenli wrote: Hello Tommy,

Yes I am using a PCI Wifi Adapter. I plug out it and I am scaned bios settings I closed almost everything except usb and Lan adapter.

And YES :) . I get Servo Thread Max Jitter is aroud 38800 and Base Thread Max jitter is around 42700.

That is much, much better.
Savaal, teshekyr, abey !
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