Input shaping - determining max acceleration

[StalkS]

Hey Everyone. I was wondering if some kind soul can point me in the right direction.  

After stepping away from any 3D printing for around a year - I've decided to say 'to hell' with worrying about the electricity costs and fired up the V2 again.

I've already made a few upgrades - Aluminum deck panels / Nevermore / KlipperScreen / CHT 0.6 Nozzle  & I'm looking to start 'successfully' pushing ABS so that I can build a StealthBurner and a few other parts (apparently a 0.6 Nozzle is not the recommended way to go Voron parts, but I would like to try anyway).

I got input shaping working and got the attached results - my question is as the acceleration suggested on both the X & Y varies enormously - '7800 for X' & '4000 for Y'   what is the best/recommended practice in this situation - go for the lowest acceleration as the limit, or is there a halfway-house option? 

Thanks in advance for anyone's input.

[Spellman]

1. The recommendation for a .4 nozzle is based around the files and dimensions of the parts are optimized for this nozzle size.  While you can use something else, I would say just slap a .4 in there to print your machine parts using a tried and true size.  Then you can try out the .6 to your hearts content afterwards.

2. Set your Hz to the suggested numbers which is the important part.  The max accel suggested is just that, you can go higher just fine, it will just be much more aggressive/less effective at higher rates.  How much so will be dependent on a number of factors: speed, accel, material, length of move.  Either way I wouldn't worry about it too much as most moves that will max this out will be internal geometry and be hidden anyway.  Outside perimeters and top skin is where it matters most, for a very high quality finish I would suggest 40-60 mm/s with an accel of around 2000, which is well below the max accel suggestions in input shaper.  In reality you can probably be more aggressive yet on outside speeds if desired.  Hope some of this helps!

[billbr]

Normally Z stays "quiet" and x and y should pretty much match. Variation between x and y curves normally indicate differing tension on the B/A belts. Your Y chart looks odd to me. How is your accelerometer mounted?  

Edited February 27, 2023 by billbr

[claudermilk]

15 hours ago, billbr said:

Normally Z stays "quiet" and x and y should pretty much match. Variation between x and y curves normally indicate differing tension on the B/A belts. Your Y chart looks odd to me. How is your accelerometer mounted?  

Interesting. I may need to redo my belt tensioning. I have both showing the same on the handy Prusa gauge, but my X/Y suggested max accel deviate quite a lot--X significantly higher than Y.

[billbr]

2 hours ago, claudermilk said:

Interesting. I may need to redo my belt tensioning. I have both showing the same on the handy Prusa gauge, but my X/Y suggested max accel deviate quite a lot--X significantly higher than Y.

@claudermilk I know there can be reasons other than belt tensions for x/Y variance (like frame tightening) I've done resonance on 5 different corexy machines (mine and others)  and was surprised to see the similarity between x and y. I would have thought than the weight of the gantry motors would skew the y resonance. Perhaps the gantry being somewhat close to the bed when doing input shaping mitigates that. I'm not a mechanical engineer so am hard pressed to explain why. Its just something I have observed.

[mvdveer]

21 hours ago, billbr said:

Variation between x and y curves normally indicate differing tension on the B/A belts

Intersting point that I was unaware of. Will need to keep that in mind on the new build.

[StalkS]

Crikey!  How did I miss all your responses! I get notifications for every other thread in the forum apart from my own - (just updated it from weekly - doh!)Thank you all for replying

On 2/27/2023 at 10:16 PM, billbr said:

Normally Z stays "quiet" and x and y should pretty much match. Variation between x and y curves normally indicate differing tension on the B/A belts. Your Y chart looks odd to me. How is your accelerometer mounted?  

It's a mount that sits just under the extruder fan - it spans the two lower screws on the Afterburner.  I'll take a look at the belt tension and try again. Thanks

Edited March 3, 2023 by StalkS

[billbr]

This discussion has made me curious. I may go dig around in the source code for an answer. The question is "Do the chart labels of x/y/z match the silkscreen on the board or match the axis that the program is vibrating? I dug out the images from my original 2.4 input shaping.  here are my charts from quite a while back. Notice that the red-line (X) in the charts has virtually no resonance. However the X+Y+Z line is somewhat telling. The X png file show the blue line (marked Z) matches the magenta line quite well. In the Y file, It shows resonance on the green line (marked Y) mostly matching on the X+Y+Z marked line. What I take from this is that the orientation reported by the ADXL is on the labels, not the direction the program is vibrating. So now I am questioning my own assertion. Can these charts indicate belt tightening difference? Hmmm... More research is needed. I read the full documentation on input shaping and found some interesting tidbits from Mr. O'Conner. :from https://www.klipper3d.org/Measuring_Resonances.html#testing-custom-axes I find that you can export the raw data for one  axis and plot it for comparisons. And in fact Kevin provides the instructions for doing belt comparisons on corexy printers in that section of the documentation (which is different from doing input shaping filters). 

 

Addendum:The X+Y+Z is all of the motion/frequencies from the ADXL summed (per the docs)

 

Edited March 4, 2023 by billbr
typo

[midmadn]

billbr - 

I used to wonder the same thing. I think klipper is intelligent enough that it determines which axis is reading which movement by the readings. I think this only because when I run a test_resonance x or y to run them individually - it gives the readings appropriately irregardless of the accelerometer's mounting direction.

I could be wrong though.

Jack

Edited March 24, 2023 by midmadn