[FR] Enable single frequency resonance testing to diagnose printer resonance

I am trying to figure out the reason why my delta printer is having both low and high natural frequencies. In order for me to figure out the culprit, I need to be able to turn on the natural frequency that klipper found for me and allow it to just ring while I say for example adjust the belt tension to see how it affects that particular frequency or hold a specific component to see how I can reduce the amplitude of the frequency. I think this would be very easy to implement with how Klipper currently tests for natural frequencies. I just need to be able to tell it to go to ex. 101Hz and it should just hold it there until I stop it. Similar concept to tuning a guitar except you are not the one to pluck any strings.

Maybe a macro could do? The job is: change 100 times/second the movement direction. If you move e.g. 1mm, you have a total of 101mm to move within 1s. So speed should be 101mm/s, acceleration as high as you dare, So the code could look like:

G0 F6060
G0 E0 X1.0
G0 E0 X-1.0
…[+99 times]

Dont’t use this! This is no propper code! Just as an idea… You need a loop and an exit criterion. But maybe as a quick help, someone can write that snippet for you?

One thing: Running any machine on its inherent frequency (eigenfrequency) is no good idea! Thing of the Tocama-bridge 1940! You might damage your printer if damping is too low… Just as a warning! (don’t do that at home :wink: )

Thank you for that idea.

While I understand what you are getting at with the bridge :slight_smile: , it would quickly show the weak point of the printer.

I do not believe, that you visibly “see” or “hear” something unusual. Maybe you should visit wikipedia to understand the “natural” or “eigenfrquency” a little bit better… You have to interprete the results and this is very, very difficult. Especially with a “strage” configuration like a hexapode you need a lot of knowledge to directly hit bull’s eye while targeting the problem.

I’d propose to close this issue, we can discuss in the forum what could be the problem. This is the wrong place to do so.

You wouldn’t be able to see indeed. You would be able to hear first what is vibrating at its natural frequency the most, therefore making the most noise. Then you can start to work your way from the housing all the way down to the effector to evaluate where to either add a damper of some sort or “tighten the screws” in order for the component to stop reaching its natural frequency at that particular frequency. You can also start touching the components while they are ringing and use your finger as a damper to figure out how dampening a certain component affects the whole system.

It isn’t a perfect computational way to do it, I understand that. But through some iterative attempts, you should be able to get close to eliminating the source of the vibrations assuming that the natural frequency is coming from a “loose screw”, and that the system wasn’t initially built with the natural frequency that is trying to be mitigated. In this case, I never had this issue before with this printer, and so there is something that I would describe as “ancillary” and not “systemic” that is causing this problem. If the printer was just built from scratch and I found these resonances, then I would agree that it would be very difficult to evaluate what is causing the natural frequency, though you can still use my method to dampen the housing, the motors, etc. to try to move the natural frequency elsewhere where it wont be reached or eliminate it.

Well it turns out that the ripples in my print were related to my extruder motor was not powerful enough to extrude the ABS fast enough.

Good to hear, that you found the root cause. But maybe you should check your whole setup again: Flow rate, print speed and nozzle diameter. “Not powerful enough” could also (in most cases) mean, that you do not reach the temperature with your setup, because the (correctly) heated filament looses most of its viscosity. Torque of the motor is used to press the fluid through the nozzle and the viscosity is one of the most important values for it (besides the flow-speed itself, sorry english seems to be very fuzzy if you do not know the right technical terms). Remember: Flow = Speed of Material * Nozzle Diameter * Density.
Example: Your heatblock is able to melt 20mm³/s of ABS
a) With a nozzle of 0,4mm your printspeed would be 160mm/s
b) With a nozzle of 0,6mm your printspeed would be 70 mm/s
The overall printtime would be exactely the same (!). So what would you like to do? Print at 160mm/s or 70mm/s?

Now the torque of your motor: the motor need to press the material through the nozzle. Let’s assume “1” to be the pressure (=torque of your motor), you need to press some material through a 0,4mm nozzle (at a certain printspeed). Using a 0,6mm nozzle, you only need 20% of this pressure (=torque) for the same volume flow (same overall printing time!! Bernoulli approach. For a 0,8mm nozzle, this drops to 6,5%!!).

Fazit: Print speed is evil, flow is your friend, use larger nozzle. (and sorry for beeing a preacher for the “Church of the holy large nozzle diameter”).

P.S. Why your are (still) printing ABS? :wink:

Thank you for the explanation Berggipfel. I know my initial response was short and to the point, but in reality to figure this out, I went through dozens and dozens of test prints. I was completely convinced that the ripples were high order vibrations. So I installed linear guide rails and switched to carbon fiber delta arms because I thought that for some reason the effector was ringing like a bell. I tried all sorts of variations of print settings.

I run a 0.6mm nozzle by the way.

What was weird is that even when I cut the speed in half, the ripples would still largely be there and I know that the printer is capable of 200mm/s prints (with the old bowden setup and high torque NEMA17)(not to mention the TBG-Lite extruder was advertised to allegedly allow 300mm/s prints, in retrospect, maybe at .1mm height) and so why in the world would I be getting ripples at 50mm/s when it used to be perfect. So I started to research adjusting chopper settings in order to take out the motor vibrations. I was able to tune the motors to be completely silent and I still would get this problem.

Finally as a sanity check, I printed using PLA instead of PETG or ABS and voila, the print did not have any ripples in it. This was the answer to the whole problem. It seems that the viscosity of the ABS is much thicker than PLA which would make sense I suppose if you consider that ABS is generally more stringy than PLA (I don’t have scientific proof of correlation between stringiness and viscosity but it makes sense to me :slight_smile: ). So I decided to keep upping the temperature on the ABS, from 220 to 250C and ripples would never go away strangely.

I started adjusting the settings on the extruder to get more torque. I kept turning down the microstepping all the way down to 1. It helped, I saw the motor struggle less, but there were still problems.

During one of the prints, I increased the extrusion factor in Mainsail and I started to see the quality of the walls greatly improve. My problem was that I didn’t want to fix the problem this way because I need the dimensional accuracy to be spot on. So I changed the print width from .55mm to .65mm and tested. The print now looks 95% better. It seems that the extruder motor needs close to 100% duty cycle to effectively push the ABS through the extruder.

Once this was sorted out, I was able to see that the extruder would not allow me print faster than ~75mm/s on the walls. I would start to hear it skip at that point.

So I understand your point about the nozzle size but I need the print resolution that comes with a 0.6mm for the type of work I do.

What’s the alternative to ABS or PETG with equivalent properties?

With all that said, I would really like to upgrade my extruder to a flying extruder setup. I have seen some setups but they rely on the arm motors to hold up the extruder still. I would like to avoid that and not add more mass to move around. I would like to be able to use another stepper motor to lift and lower an extruder close to the effector. I know that Klipper has a “MANUAL_STEPPER” option but I don’t think it has the commands needed for the stepper to track the Z-position and track it.

For example while printing the ringing_tower, you are able to tell Klipper to adjust acceleration a certain amount for every 5mm of z position move. Would it be possible to have this manual_stepper do the same and just move up 1mm for every 1mm change in z-position? This would help solve a lot of problems in the delta printer community I would think. Any help with this would really be appreciated.

Great to hear, that you really worked on the problem…and finally solved it. It is always a problem for any remote help, since in 50% of the cases, the final information is just not available for you…

0,6 is my choice, so everything is ok with this (you are now Padawan of the “Church of the holy large nozzle diameter”!)

Alternative to ABS is hard to define without knowing your requirements. If you have more or less none, use PETG always. Today you can buy PETG that goes until 85°C (see https://www.extrudr.com/filerpool/download/datei/982/ it is german, but a technical data sheet) so temp is no longer an issue. if you want it with more elongation at break (=capability to resist enlargements without breaking), you may use PETG (up to 28%) or PCTG (datasheet: 200% but my tests didn’t show this). But what you get is

For the manual stepper, maybe others could help you, sorry i am not conterminated with this knowledge…

Haha well I am glad that the Church of the holy large nozzle diameter accepts me.

I have been using both ABS and PETG. I have an enclosed delta and rather than using a consumable like activated carbon to filter the air, I have a 120mm centrifugal fan pumping air through a hose outside the house and all is good now. No more fumes in the room.

I will start another thread about the manual stepper setup

I appreciate your time and commentary. Thank you

Mr. Administrator: I think we need a badge “Member of the Church of the Holy Large Nozzle” :wink: Two Members until today…