CoreXY - X-Axis Vibration Issues

fcwilt · 1 Apr 2019, 05:10

@zapta said in CoreXY - X-Axis Vibration Issues:

Was your printer already setup with a 24 volt power supply?

Yes, all parts are on 24V, including heaters and fans, no buck converters and such. The only add-on is this SSR to reduce heat on the Duet https://www.auberins.com/index.php?main_page=product_info&products_id=288

And I just finished tidying up the wiring on my 12 volt setup making the conversion a bit more work. Sigh...

So, let's see, I need new heaters, new fans, new steppers and a new bulb for my illuminated emergency stop button...

Thanks for the info.

Frederick

Veti · 4 Jan 2019, 13:43

@zapta said in CoreXY - X-Axis Vibration Issues:

I just install same 0.9 stepper as the (x-y) motor of my printer and the vibrations of the (x-y) diagonal movements test are gone! I have another one on order for the (x+y) motor. It seems that 0.9deg steppers do make a difference.

Same for me. But can anyone give an explanation as to why this solves the problem?
My current theory is that the microstepping can not hold the inbetween steps in all cases.
i.e at some steps closer to the full step the holding force is not great enough which causes the driver to move/remain at the full step resolution. causing more filament to be extruded at the full step position.

edit: found this https://www.machinedesign.com/archive/microstepping-myths

zapta · 1 Apr 2019, 15:34

@fcwilt said in CoreXY - X-Axis Vibration Issues:

And I just finished tidying up the wiring on my 12 volt setup making the conversion a bit more work. Sigh...

And I just tied up my wiring, which resulted in the SSR giving up smoke and dying. Apparently I connected the control input in reverse polarity.

This was an opportunity to look inside the SSR. It's built like a tank and the power Mosfet has a large chunk of silicon in it.

Connected the 12A/24V bed to the Duet directly and everything works like champ. Not sure if I want to install a new SSR. I like the current simplicity.

zapta · 1 Apr 2019, 16:39

@veti said in CoreXY - X-Axis Vibration Issues:

Same for me. But can anyone give an explanation as to why this solves the problem?
My current theory is that the microstepping can not hold the inbetween steps in all cases.

I think that my experiment of having vibration in a single stepper diagonal move (I as actually holding the other belt with my finger to make sure that there are no vibrations from the stationary motor) supports that this is not necessarily a result of an interaction between the two motors.

Your explanation sounds reasonable to me. Microstepping and Interpolation have their limits, especially that it is a modulation of the underlying PWM and not direct linear current source.

Another potential factor is that the 0.9 steppers are also larger (for same torque) and thus have higher mass and smoother rotation (?)

Veti · 4 Jan 2019, 18:19

i found this very good analysis of microstepping https://hackaday.com/2016/08/29/how-accurate-is-microstepping-really/

dc42 · 2 Apr 2019, 10:21

@zapta said in CoreXY - X-Axis Vibration Issues:

Connected the 12A/24V bed to the Duet directly and everything works like champ. Not sure if I want to install a new SSR. I like the current simplicity.

12A is well within the rating of the Duet. I recommend that at regular intervals you check that the screws in the VIN and bed heater terminal blocks of the Duet are still tight, until you are sure that they are staying tight. This is because high currents can cause creep in wires. Crimping the correct ferrules on to the wire ends reduces this risk.

fcwilt · 2 Apr 2019, 12:51

@zapta said in CoreXY - X-Axis Vibration Issues:

Connected the 12A/24V bed to the Duet directly and everything works like champ. Not sure if I want to install a new SSR. I like the current simplicity.

My heaters are all line voltage heaters (110 VAC) and thus an SSR is needed.

Frederick

zapta · 2 Apr 2019, 17:21

@dc42 said in CoreXY - X-Axis Vibration Issues:

12A is well within the rating of the Duet.

Yes, it seems to handle it very well and the mosfet is cool even at 100% PWM (looked at it with an IR camera).

I did crimp cheap Chinese ferrules, hope they are right, they seem to be made of aluminum(?). Not sure how it will behave when oxidized. I know very little about it

dc42 · 2 Apr 2019, 18:20

@zapta said in CoreXY - X-Axis Vibration Issues:

Yes, it seems to handle it very well and the mosfet is cool even at 100% PWM (looked at it with an IR camera).

The rated bed heater current of the Duet isn't set by the MOSFET, it's determined by heating of the PCB traces. Even when using 2oz copper instead of the usual 1oz, and duplicating traces on both sides of the PCB, it's hard to carry 20A on a PCB.

zapta · 2 Apr 2019, 20:04

@dc42, I presume you are aware of this technique but just in case

http://www.eevblog.com/forum/blog/eevblog-317-pcb-tinning-myth-busting/

Veti · 6 Apr 2019, 16:45

we have a name. VFA (Vertical Fine Artifacts)

https://shop.prusa3d.com/forum/user-mods-octoprint-enclosures-nozzles--f65/stepper-motor-upgrades-to-eliminate-vfa-s-vertical-t28098.html

it seems if you make your printer more precise these artefacts start to show.

after getting an ender 3 to play with i found these artefacts as well on the ender 3.
funny thing is the user started seeing the problem around the same time.

dc42 · 6 Apr 2019, 19:52

@zapta said in CoreXY - X-Axis Vibration Issues:

@dc42, I presume you are aware of this technique but just in case

http://www.eevblog.com/forum/blog/eevblog-317-pcb-tinning-myth-busting/

Yes, but it's not very effective, especially if you are already using 2oz copper.

zapta · 6 Apr 2019, 20:59

@dc42, yes, this is a good point. Doubling the copper thickness doesn't double the solder.