Problem with V2.6 upgrade and rotation axis not limiting to +-180 degree

[andrew...@gmail.com]

Was not having this problem with v2.4

The problem does not occur if I limit placements to one nozzle.

If I run a job with two nozzles being used some parts get put down at wrong rotation and the silicone tube get knotted up.

I looked at the logs and I get RED lines that say

"2026-03-19 21:12:58.553 AbstractMotionPlanner$SubordinateMotion WARNING: Subordinate Motion queue not empty: (C1:88.276618), drained."

I have the C1 and C2 axis set to limit 180 degrees.

What am I doing wrong?

[Mike Menci]

You need to use Vaccum rotating coupling at top of steeper motor shaft connecting to vacuum tube 

Dne 19. mar. 2026 ob 11:38 je oseba andrew...@gmail.com <andrew...@gmail.com> zapisala:



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<knotted_tube.jpg>

[andrew...@gmail.com]

I did buy some of those couplings but never used them because they didn't work great.  So instead I just used very flexible silicone hose.

The machine has run for many many years using the silicone hose without this problem.

OpenPNP version 2.4 did not have this problem.  If the nozzle was at 170 degrees and has to go too 190/-170 it would go the long way around.

I actually don't understand how it keeps twisting around as the Duet3D config sets the max rotation at +-190

BUT even if I did have a rotary coupling - It would not fix the wrong angle part placements that happen long before the hose gets twisted.

For example - I have a board that has two SOT23-6 USB-ESD-Arrays.

If I mark all small components (0603) on the board as disabled then these SOT23-6 both get placed correctly with the right-side nozzle.

If I allow the machine to run with both nozzles (placing 0603 Rs at the same time) the second SOT23-6 always gets placed 180 degrees wrong.  Not some random angle like missed steps/slipping-part would make.  Perfectly bottom-vision-aligned-and-180-degree-wrong

[Mike Menci]

Than you don’t have step/ mm - rotation set up right - remove the hose and test 360 deg - 1 turn 

Poslano iz iPhon-a

Dne 19. mar. 2026 ob 13:25 je oseba andrew...@gmail.com <andrew...@gmail.com> zapisala:



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[andrew...@gmail.com]

Nope - I have steps per degree set up fine.  I know this because I spent 3 days trying to work out why I could not calibrate camera/nozzles after upgrading to the Duet Mini Mr Black gave me.

I had different steps per mm on Mr Blacks toolhead than the old Smoothie had for C axis.  So when commanded to do 360 degrees it was moving 720 degrees.  So I have already had a problem with steps/mm and fixed it.

But I also just checked it now.  If I go to OpenPNP jog tab and move 180 degrees a sharpie mark I placed on the pulley rotates 180 degrees real world.  If I try JOG to 190 degrees the head spins opposite direction to get to -170.

Also if I go to Duet control panel thing on my web browser and I jog past the hard limit in the config file - I get told

"Error. G1: target position outside machine limits"

So I actually have no idea HOW openPNP is managing to spin the C1 axis around 3+ full turns because the Duet hardware tries to limit it.

I thought "Maybe it is loosing C axis steps in one direction" so I ran a job at 10% speed and it still happened.

However if I run a 100% speed job split in two parts "All small 0603 parts for C1 axis / N1 nozzle" and then a 2nd half job with all parts for C2/N2 it motors along quickly and perfectly places all the parts.

It MAY be a strange interaction with Mr Blacks tool head which is also a fairly recent upgrade.  However I only change ONE thing at a time on my machine and it was running fine and placed 50 of this exact same board without a problem on V2.4

So upgrade path steps 

Built machine 10ish years ago using a smoothieboard and always had problems with X/Y drift with small C moves but dealt with it to make 500+ of this exact same board.

Moved from Dining Philosopher feeders to push pull feeders - Ran 100+ boards fine

Upgraded my bottom camera to the new coaxial light I made - Ran 80+ boards fine - much better placement with the new coaxial camera

Upgraded from Smoothie to the awesome Duet 3D Mini with Wayne Blacks CAN tool head - Ran 50+ boards fine (after fixing my step per degree problem)

Upgraded to OpenPNP V2.6 - have struggled to make 10 boards because the silicone hose that has been present for 700+ boards keeps getting twisted in spite of Duet hardware trying to limit rotation to +/- 190 degrees

When I upgraded from V2.4 to V2.6 I did not import my old machine file - I started from scratch with "Issues and Solutions" to remake the machine config.

So It is probably something dumb I have done in that step - I just can't work it out - or understand how C1 can spin 1080 degrees when Duet has a hard limit of 190 degrees.