Polar Printing: Polar Axis Rotation Issue

[reprapper]

Hi all,

I’ve setup a polar printer on the Creality CR-10 just as a learning experience.

Following the guide outlined (https://duet3d.dozuki.com/Wiki/ConfiguringRepRapFirmwarePolarPrinter) I’ve been able to get it up and running. An issue that I am running into is that if the polar axis rotates over a certain angular position then the print stops for about 10s before resuming and continuing the print. I am unable to confirm if this is at the angular position 0/2pi rad, however, this would seem like the most plausible position. This pause occurs rotating in either direction and also during travel moves.

This video shows the pause during a printing move: https://drive.google.com/open?id=13Qj13-Mbc08P1ego272jXPiLEMTOrbtV
This video shows the pause during a travel: https://drive.google.com/open?id=1O9Eta8F2TTrEmmupU9bnrWBSLBsu7jKQ

If the print does not need to rotate through this position, then everything works as expected.

I am using a Maestro 2 with Firmware 2.02(RTOS) (2018-12-24b1). This is my polar config:

Is this an issue in the firmware or is there something wrong in the setup?

Martin

[fcwilt]

Hi,

What's in your homing files?

Frederick

[dc42]

@reprapper , congratulations on being the first person I am aware of to use the Polar support in RRF!

I agree, it looks like a firmware bug. Can you confirm that the centre of rotation of the bed is somewhere inside that square shape you are printing? Edit: I just realised that's a stupid question, it must be inside otherwise it couldn't print a square without reversing the direction of rotation.

[dc42]

I found the problem. The main kinematics calculations have worked out that it needs to take the short route between -179 and +179 degrees, but the speed and acceleration limiter in the PolarKinematics class thinks it is going the long way round. So it's reducing the speed for that bit to about 1% of normal. Now I just need to fix it.

[dc42]

@dc42 said in Polar Printing: Polar Axis Rotation Issue:

I found the problem. The main kinematics calculations have worked out that it needs to take the short route between -179 and +179 degrees, but the speed and acceleration limiter in the PolarKinematics class thinks it is going the long way round. So it's reducing the speed for that bit to about 1% of normal. Now I just need to fix it.

Meanwhile, you could use this "feature" to calibrate pressure advance, i.e. see what value of pressure advance improves the print the most.

[dc42]

I believe this issue is now fixed and I have put a new firmware binary at https://www.dropbox.com/s/m0r3ldy424mxf4v/DuetMaestroFirmware.bin?dl=0. Caution: this firmware contains some unrelated changes that have not been fully tested, so use it with care.

[reprapper]

@dc42 Thank you for the amazingly quick response! The firmware binary fixed the kinematic issue.

Still lots of tuning and tweaking to do but the kinematics seem to be working correctly now.
Here's a short video showing what polar's do best, printing vases: https://drive.google.com/open?id=1T2Wjb3OejqWlkfOUjZREdYk8xY59UvRD

@fcwilt My homing files are the same as outlined in the polar setup guide: https://duet3d.dozuki.com/Wiki/ConfiguringRepRapFirmwarePolarPrinter

[pir2z]

@dc42 Hi David, I see Polar are the hight problem... I have exactly the same effect on the Duet Wifi, please could you find the same solution on it?
Thank for all.
Best regards
Pierre Zanetti

[dc42]

@pir2z said in Polar Printing: Polar Axis Rotation Issue:

@dc42 Hi David, I see Polar are the hight problem... I have exactly the same effect on the Duet Wifi, please could you find the same solution on it?
Thank for all.
Best regards
Pierre Zanetti

I'm sorry, I don't understand what problem you are having. Please explain.

[pir2z]

@dc42 Sorry for my english level... I met the problem explained above. When Y=00 , the printer does a long stop (no error occured). After many seconds all restart.
I hope I'm clearer now.
Thank a lot
Pierre

[dc42]

Try this firmware https://www.dropbox.com/s/fyvibzm0zl92hiy/Duet2CombinedFirmware.bin?dl=0

[pir2z]

Thank a lot I try it and I keep you in touch. Thank for all

[pir2z]

Hi David,
I tried the new version you sent me and unfortunately it doesn't work.
The starting problem is not resolved and the movements are very jerky now.
The movement does a "stop" when heater is arround Y= 0 (between -0.5 and +0.5) it's not very constant.
I would like to know if it can come from the mathematical problem between radian or degree, or a division by 0.
let me know what I can send you to help you to analyse my problem.
Best regards
Pierre

[dc42]

Please try version 2.03beta2.

[pir2z]

Hi David, Ok I'll try it and keep you in touch.
Thank for all

[timcurtis67]

@dc42 said in Polar Printing: Polar Axis Rotation Issue:

I found the problem. The main kinematics calculations have worked out that it needs to take the short route between -179 and +179 degrees, but the speed and acceleration limiter in the PolarKinematics class thinks it is going the long way round. So it's reducing the speed for that bit to about 1% of normal. Now I just need to fix it.

Just out of curiosity, Is it possible the issue relates to 180 degree moves? Would dropping or forcing 90 degree moves help with the long pauses?

Maybe none of this is related but back in "the day" a lot of program movement issues could be cured by forcing arc type move to be broken into 90 degree segments.

Again, disregard this post if none of this applies to the current issue.

[dc42]

@timcurtis67 said in Polar Printing: Polar Axis Rotation Issue:

Just out of curiosity, Is it possible the issue relates to 180 degree moves? Would dropping or forcing 90 degree moves help with the long pauses?

No. But I fixed this issue in firmware 2.03beta1.