How to Tune Your Motion Parameters

[lars86 42]

Hi guys,

I started writing a reply to an old thread about excessive "ringing" on the UM2 vs UMO. Then is just kept writing and writing, and eventually I decided to just start a thread about this! hahaha

This should be helpful on any machine really, and can serve as a generalized guide for machine motion tuning. Feel free to ask questions, or correct any errors.

I think that many are proud of how high they "can" run max accel values, but I am very much of the opinion that there is a sweet spot well short of that.  I run my UMO++ acceleration at 1600mm/s^2, and jerk at 12 for X & Y. I feel like this gives very crisp motion, without beating everything up.

If the concern is saving time, increasing acceleration is not a reasonable way to achieve this. You would be far better off tuning acceleration for better motion, and running faster print speeds.

Force exerted on the drivetrain components is directly proportional to acceleration, so the higher max acceleration is set, the more likely you are to exploit lash in the system, or make a more permanent alignment shift (belt slipping in an XY block or against the pulley, pulley shifting on the shaft, stepper shifting in relation to the frame, etc). Also, as I'm sure you guys have seen, there is a natural resonance to the carriage system. Everything supporting and driving the printhead acts elastically (the 8mm and 6mm shafts, the belts, the printhead itself).  

Printing in one of the back corners helps reduce vibration from the cantilevered bed, and deflection of both sets of shafts. The shafts flex most in the middle, and least where they are supported (frame mounted bearings, and XY block attachments). Printing in the middle of the bed encourages the print head to whip around, riding the wave of the shaft flex, so moving to a back corner reduces ringing two times over.

The driving belts still have the same force exerted on them and elongation from it, in any print position. Reducing max acceleration is the best way to combat this.

I encourage everybody to test and tune on their own machine and find the best settings for you. Customizations will have a big impact on machine behavior, especially total mass of printhead (different hot ends, XY blocks, printed heads, fans, etc), since force is also directly proportional to mass.

The print itself has a big impact on how much the acceleration settings affect things. A good test part would have some big and small vertical holes, sharp OD / ID corners, narrow rectangular sections. I whipped up a model but haven't tested it yet. Feel free to make suggestions on additional features!

Start with a print speed / layer height that you use frequently, and print one of these with your current settings, as your baseline. Don't run slow outside/inside perimeters, as we don't want to hide acceleration effects. Keep speeds of everything equal.

I suggest 100% infill, 2 perimeter walls, and a filament / temp combo you are comfortable with. Pick a filament that prints very well for you and shows good detail. Then print one with 1600 accel on X&Y and jerk at 12. See what you think of the results.

Once you have some data points, play around with the settings mid print. Listen to the machine, feel the vibrations through the frame. The motion should be quick and clean, without jarring or vibrating everything. If your accel/jerk is too low, you will see over extrusion in the narrow infill sections. If it is too high, you will see evidence of ringing (like an echo in the print surface) during sharp direction changes.

For reference:

• Max acceleration: maximum change in velocity per unit time.
  
• Jerk: maximum change in velocity allowed without being bound by max acceleration. Think of it as a "bypass" on acceleration, so be careful here. I would start with this value low (12 or less), get your acceleration well tuned, then increase this and watch/listen to the printer.
  

Edited June 15, 2015 by Guest

[lars86 42]

https://www.youmagine.com/designs/max-acceleration-tuning-print

[valcrow 144]

I usually print small detailed angular things, this has been a huge thing I've been toying with over the years. Frame rigidity & the surface it sits on plays a big part in it too besides just the acceleration. The more micro 'wobbles' the worse it gets for small 90 degree angles.

like you I've found around 1500 works best for UMOs.

I run 2300 on my UM2's

and leave the default 4000 on the UM2GO.

The small frame of the UM2GO lets that thing go at full speed without introducing much ringing artifacts. it's awesome.

While lowering acceleration helps the ringing artifacts, it seems to affect the top surface quality. It slows down as it reaches the perimeter sometimes creating thicker fills near the edge, and thinner (sometimes apparent line separations) in the center top of your print. So consider this when making big flat top objects.

UMO print at 4000 acceleration

UM2 Print at 1500

For your ringing test, consider adding some small grooves on the side. That stuff rings like mad.

Edited June 15, 2015 by Guest

[lars86 42]

I usually print small detailed angular things, this has been a huge thing I've been toying with over the years. Frame rigidity & the surface it sits on plays a big part in it too besides just the acceleration. The more micro 'wobbles' the worse it gets for small 90 degree angles.

like you I've found around 1500 works best for UMOs I find.

I run 2300 on my UM2's

and leave the default 4000 on the UM2GO.

The small frame of the UM2GO lets that thing go at full speed without introducing much ringing artifacts. it's awesome.

While lowering acceleration helps the ringing artifacts, it seems to affect the top surface quality. It slows down as it reaches the perimeter sometimes creating thicker fills near the edge, and thinner (sometimes apparent line separations) in the center top of your print. So consider this when making big flat top objects.

For your ringing test, consider adding some small grooves on the side. That stuff rings like mad.

 

Nice photo! That really helps illustrate the ringing effect.

It's cool to see you land very near to me on max acceleration, independently. I agree on the top layer infill aspect as well. I think the narrow rectangular infill section on my part should provide an exaggerated version of that, since the head is constantly in a state of acceleration, likely never hitting commanded feed. If you can find a setting that provides fairly uniform extrusion on this test part, there shouldn't be a worry on a live part.

On the grooves, do you mean a vertical, square profile groove? I could definitely add those in, but was thinking that the two 90* OD corners would show the same thing. One corner shows the Y axis coming to a rapid stop, with a pure X move following to show any ringing. the other corner shows X stopping. Thoughts?

Edited June 15, 2015 by Guest

[neotko 1,417]

One question about this. Placing a clamp on the 3 open sides of the umo to the table (heavier) could help to transport the movement force from affecting the print rings?

[lars86 42]

One question about this. Placing a clamp on the 3 open sides of the umo to the table (heavier) could help to transport the movement force from affecting the print rings?

 

If I understand you correctly, you are talking about adding mass to the build platform.

This really won't help "ringing", since the primary factor in ringing is the 6mm and 8mm printhead shafts flexing.

It would help slow vibrations in the bed, and I have done it before I upgraded to the heated bed. It won't eliminate the vibrations though. You are better off trying to make the bed more rigid.

[neotko 1,417]

Ok finally found the post where this was said. It was a post of @gr5 2 years ago

"Or clamp the frame of the UM to a 400 pounds weight."

https://ultimaker.com/en/community/view/3532-prevent-ringing-wobbly-surface-after-sharp-corners?page=2#reply-19017

So adding mas to the box might help absorb the movements? Maybe a 3 sides clamp and some flex material on the foot of the table?

[lars86 42]

Ah, gotcha!

I have played with that too. I used to keep a heavy metal plate in the bottom of my Ultimaker, and have also clamped it to a workbench before.

It can definitely help keep things a little more still and quiet, but you have to be careful. Since the UM sits on 4 feet, you can easily overconstrain the bottom plane when clamping. Basically, it only takes 3 points to define a plane, so when you have 4, the fourth needs to very closely match the plane defined by the other 3, or it will not touch the ground ( like a wobbly table at a restaurant). If you clamp everything down, there is a good chance that you force the whole frame to flex in order to put the 4th point down. This would be much worse than a little vibration.

My thought is that any print head accelerations fast enough to shake the frame, are also powerful enough to flex the 6mm/8mm shafts. Clamping the frame down won't fix this. You are better off to tune the motion parameters to avoid acceleration this high, and maybe add a bit of weight to the UM floor if you want a little more help.

[neotko 1,417]

So maybe a 4 clamp system with a flex or soft support to compensate the woobly. Sounds nice to try. I have a lot of ringing even at 1600/15yerk and even at 1000. It's probably the wooble pulleys so I'll design a clamp flex and test it. Also I'm going to change to gt2 and that will probably change the picture but since I want to print at high speed to increase a production/time/decent quality I want to improve anything that can make me stay faster. Thank tou for your output!

[gr5 2,173]

How do you know if the ringing is mostly caused by the shafts or in the rubber belts?

Well I guess we could think about the frequency. I'm going to estimate the frequency within about a factor of 10. Looking at the companion cube I'm going to say the rings are 1mm apart and guess the head was moving at 50mm/sec (much faster and it would have been still accelerating and they should be noticably closer together nearer the edge when head is moving slower).

So that's 50 rings per second (50mm/sec divided by 1mm). That's a very low frequency - I doubt those steel shafts wobble that slow - much morel likely the belt I think. And if you double the tension on the belt the frequency should double (lines twice as close together).

Now this is rough so it could be 10Hz up to maybe 200hz. Those are mostly audible frequencies (low pitch) and again the belt is about right for that.

[valcrow 144]

I think the ringing actually comes from the frame. I'm not entirely sure though I'm just a graphics nerd.

Reason being, if on an unstable table, the ringing gets noticeably worse when the thing is allowed to shake more. (and the whole table does it shake!)

Another reason is, if I hold the frame, being a squishy human, absorbing some of the vibration motion, it noticeably dampens the ringing effect for the few layers that I did hold it. So I think it has to do with the resonance of the whole box. This shouldn't technically affect belt ringing if it was caused by that yes?

When you turn acceleration down to 1500ish, the frame doesn't shake NEARLY as much even on a shaky table.

[neotko 1,417]

 

@valcrow here another graphics designer nerd. I have the same felling. Also noticed that when I watch the printer placing my body weight over the table I see less ringing. That also why I asked about the idea of clamping the wood frame to the table. Maybe it's just that our bodys absorb the shock so it doesn't go back to the machine. If it's so then maybe a sand bag under the box or a visco-elastic foam support might help more (no kidding)

Edited August 4, 2015 by Guest

[gr5 2,173]

@valcrow - well if what you say is true (I trust you!) then I would guess the next most likely thing to cause the ringing would be vibrations in the bed or at least the bed relative to the head. Well I guess we know that 100% - somewhere between the part (which is sitting on the bed) and the head there is ringing - maybe most of it is in the bed. But I would expect more ringing on the sides and less on the front and back.

[neotko 1,417]

@gr5 do you mind a question?

I been wondering on my head about this for two weeks.

Umo/umo+ central 6mm shafts are shorter than the ones UM2. I was wondering since each side block has extra 'shaft' on the sides. (apart of the gt2 pulley/belts) if that's a method the um2 uses to remove more vibrations that go from a drastic change of movement to an area that it's on the air.

I just think it on my head and I think it make's sense. Does it?

[lars86 42]

@gr5 do you mind a question?

I been wondering on my head about this for two weeks.

Umo/umo+ central 6mm shafts are shorter than the ones UM2. I was wondering since each side block has extra 'shaft' on the sides. (apart of the gt2 pulley/belts) if that's a method the um2 uses to remove more vibrations that go from a drastic change of movement to an area that it's on the air.

I just think it on my head and I think it make's sense. Does it?

 

I don't have an UM2, so I had to look up pictures, but I fail to see any 6mm shaft cantilevered out like you've drawn. Doing so might change the vibration characteristic a bit, but wouldn't serve to reduce vibration.

[neotko 1,417]

No no sorry. I mean the drawing as an exhaggeration of how the forces distribute when a full stop on the shafts.

[gr5 2,173]

On the UM2 the 6mm rods snap in and out of the blocks in seconds. You can flip the head upside down or mount it "ass backwards" in about 15 seconds.

The rod parallel with the X axis is long and sticks out past the blocks. The Y axis does not and doesn't stick out past the blocks. This is because the X axis rod is what hits the limit switch when homing. I don't think it has anything to do with dampening vibrations. But it's good that you think about things like this.

[SJDrummond 1]

Jumping in a little late here, has anybody tried using a material such as dynamat?

I know its supposed to be for audio purposes but its main feature is that it absorbs vibrations.

I haven't got a before and after shot of ringing, but I have stuck a sheet on the back of my UMO and i don't have too many issues with ringing. Admittedly, I stuck it on to try and reduce the noise the machine made but it could aid the vibrations also?

[gr5 2,173]

The vibrations I believe are mostly from the belts which can stretch a bit like a rubber band so I don't think that would help. Putting a box of sand with interior baffles on the print head should help but then you will have to lower the acceleration also most likely. Some newer boards limit "true jerk" and don't have these problems such as the tinyG controller board.