nanoDLP

reinventtheprintingpress

Member

Registered: 2019-06-12

Posts: 5

Help! Bizarre Z Axis Behavior

Hi long-time lurker, first-time poster!

Building my first SLA DLP Printer and working with this current build - a Raspberry Pi 3 B+ paired with a RAMPS 1.4 w Mega 2560 - Pololu a4899 as the drivers. The Z Axis is a simple CNC stage using a NEMA 23 as a motor.

For guidance I used the MUVE3d setup guide, running their recommended patched Marlin on my rig and the NanoDLP Muve configuration.

So far so good - after playing with the settings I managed to get a decent print. I noticed how squashed it was - in fact, the print was about 40% shorter than normal (ie 6 mm tall instead of 10).

So I checked how far my stage would move - indeed, inputting 10 mm via the Z Axis control or into the RAMPS terminal would produce around 6 mm instead.

Unbelievably, I had not changed the leadscrew settings - it was 8 mm per turn instead of 5 mm. .... it changed *nothing*.

Most interestingly, I had noticed that sending commands to move the motor from home to something like 10 mm higher it would rocket up to the top of the stage (I have a top down system w home on the bottom). Another example is I would send it up 10 mm three times, and the third time it would go *down*. I had heard that Z Axis control could be wonky - but it might be a symptom of a major issue.

I checked every single element of my design. Wiring was correct, jumpers set to 1/16 (all set pins are tied), the VREF is set to 0.8, etc.  I reuploaded Marlin and that didn't make a difference either. Seems like everything is as correct as can be.

Is there anything I am doing wrong?? I care share my settings to see if I can get some help here - i am SO close to getting my machine going , so I'd appreciate some help!

Last edited by reinventtheprintingpress (2022-11-10 15:48:44)

Shahin

Administrator

Registered: 2016-02-17

Posts: 3,541

Re: Help! Bizarre Z Axis Behavior

Looks like RAMPS firmware is not configured correctly.

reinventtheprintingpress

Member

Registered: 2019-06-12

Posts: 5

Re: Help! Bizarre Z Axis Behavior

Ah thanks for the clue Shahin! NanoDLP is the bomb and thank you for the work thus far!

I think I fixed the issue - So I looked into the config on the Muve3D Marlin settings - I searched for the word 'steps' to help me out.

I found this code in config.h

//#define DEFAULT_AXIS_STEPS_PER_UNIT   {36.36,36.36,640,640}  // default settings for for mUVe 1-1.1
#define DEFAULT_AXIS_STEPS_PER_UNIT   {36.36,36.36,400,400}  // default settings for for mUVe 1.5 or if you have the leadscrew upgrade

First hint is the difference in leadscrew in the comments - it's possible my leadscrew is different from anything in the Muve3D. Also, 400 steps instead of 640 steps would provide a figure of roughly 0.6 - I've been seeing a discrepancy of 60% of the total distance the axis should move.

So i swapped the code out to this

#define DEFAULT_AXIS_STEPS_PER_UNIT   {36.36,36.36,640,640}  // default settings for for mUVe 1-1.1
//#define DEFAULT_AXIS_STEPS_PER_UNIT   {36.36,36.36,400,400}  // default settings for for mUVe 1.5 or if you have the leadscrew upgrade

Reuploaded RAMPS and tried again - it seems to move 10 mm when i ask it to!

However, the Z control is really weird - it will move large motions still when i dont ask it to. People have noted this issue so I assume that this isn't a big deal - im going to try printing and see how the results works out.

Thanks!