gwhite
Posts: 102
Joined: Wed Jul 19, 2017 9:37 am

Cooling Fan Override for Short Layers Not Working?

Mon Nov 26, 2018 10:38 am

I've been battling with a small PETG print. The top features is a round pin about 5mm in diameter. I've got the settings dialed in nicely for the larger lower sections of the model, but when it gets to the pin, it makes a mess. The defects were consistent with the previous layer still being molten and getting dragged by the extruder when the next layer got printed.

I've been running the majority of the print with no cooling. The pin section takes about 7 seconds to print a layer, and I had the "Increase fan speed for layers below" set to 5 seconds and 60% cooling.

I went in and forced the fan to come on at the layer where the pin feature starts. I tried 45% cooling and 75% cooling, and they both made a HUGE improvement in the quality of the print, with 75% being slightly better.

Here are before & after pictures of the pin (the model has been chopped down just to test this issue):
Bad Pin.jpg
Good Pin.jpg
I haven't verified this visually, but all indications are that the "Increase fan speed for layers below" X seconds setting isn't doing anything. Is there some weird issue with starting with 0 cooling, or am I missing something else? From what I can see, this looks like a bug. If not, then what am I misunderstanding about this feature?

wirlybird
Posts: 1216
Joined: Sun Jul 17, 2016 1:32 pm

Re: Cooling Fan Override for Short Layers Not Working?

Mon Nov 26, 2018 11:18 am

What is the printer?
See if the box for "Blip to full speed …" is checked. Might help. Maybe the fan can't get spinning slowly?

blackbird2016
Posts: 134
Joined: Wed Aug 02, 2017 1:24 am

Re: Cooling Fan Override for Short Layers Not Working?

Mon Nov 26, 2018 12:30 pm

gwhite wrote:
Mon Nov 26, 2018 10:38 am
The pin section takes about 7 seconds to print a layer, and I had the "Increase fan speed for layers below" set to 5 seconds and 60% cooling.
Since the layer time is more than your 5sec threshold it does not kick in...

gwhite
Posts: 102
Joined: Wed Jul 19, 2017 9:37 am

Re: Cooling Fan Override for Short Layers Not Working?

Mon Nov 26, 2018 3:20 pm

blackbird2016 wrote:
Mon Nov 26, 2018 12:30 pm
gwhite wrote:
Mon Nov 26, 2018 10:38 am
The pin section takes about 7 seconds to print a layer, and I had the "Increase fan speed for layers below" set to 5 seconds and 60% cooling.
Since the layer time is more than your 5sec threshold it does not kick in...
Boy do I feel dumb... I think I've been working too late on this thing. Let me kick it up to 10 & see if that fixes it.

Thanks!

gwhite
Posts: 102
Joined: Wed Jul 19, 2017 9:37 am

Re: Cooling Fan Override for Short Layers Not Working?

Mon Nov 26, 2018 3:22 pm

wirlybird wrote:
Mon Nov 26, 2018 11:18 am
What is the printer?
See if the box for "Blip to full speed …" is checked. Might help. Maybe the fan can't get spinning slowly?
It's a MakerGear M2E. I've got the "blip" box checked.

Blackbird pointed out that I had the timing messed up. I'm pretty sure that will fix it.

wirlybird
Posts: 1216
Joined: Sun Jul 17, 2016 1:32 pm

Re: Cooling Fan Override for Short Layers Not Working?

Mon Nov 26, 2018 3:37 pm

I agree with the timing! I missed that!

gwhite
Posts: 102
Joined: Wed Jul 19, 2017 9:37 am

Re: Cooling Fan Override for Short Layers Not Working?

Tue Nov 27, 2018 11:30 am

"A beautiful theory shot down by an ugly fact..."

I set it to 10 seconds, and the cooling is still not kicking on. In the meantime, I tried forcing 100% cooling on the top section and it looks great.

I'll try 15 seconds & see what happens. Despite my earlier brain fart, I still think something isn't working right. I can watch it more closely today, and I will use a stopwatch to be certain of the layer timing.

blackbird2016
Posts: 134
Joined: Wed Aug 02, 2017 1:24 am

Re: Cooling Fan Override for Short Layers Not Working?

Tue Nov 27, 2018 1:10 pm

Just check on your gcode with a text editor and search for the M106 Sxxx command
to check whether the fan gets powered.
If you are with 4.1.0 I recommend to try that with 4.0.1, the new release is kind of buggy...
Edit:
Works even in 4.1.0
If you would like to provide your factory fil we could check on that matter...

gwhite
Posts: 102
Joined: Wed Jul 19, 2017 9:37 am

Re: Cooling Fan Override for Short Layers Not Working?

Tue Nov 27, 2018 2:55 pm

It's working, but the amount of cooling seems to be proportional to how short the layer print time is relative to time limit. This is also complicated by the fact that at speeds under about 40-45%, my fan won't run at all because the internal fan drive/motor hardware doesn't respond linearly to the PWM fan signal. It will run OK at 45%, but it won't start at 40% without a push. The "blip" command should fix that, but "40%" is barely turning over. You certainly don't 40% of the amount of max cooling.

Here's what I've observed:

The layer time is definitely a bit longer than I thought, but it's under 10 seconds (~ 9.5 seconds). I have the "maximum speed" set to 100%.

With the limit threshold set to 10 seconds, there is no significant effect. I didn't watch this one, but from the print quality, if it tried to use the fan at all, it didn't set the speed above 45% and nothing happened.

With the limit threshold set to 15 seconds, the fan comes on. However, the amount of cooling is definitely less than 100%, and I still get significant defects in the print.

With the limit threshold set to 20 seconds, the fan comes on. The amount of cooling is much better than at 15 seconds, but it's still definitely less than 100%. The print defects are reduced a lot from no cooling, but still no where near as good as forcing 100% using the starting layer of the top section.

I'm not quite sure what S3D's algorithm is, but it's definitely NOT " go to maximum cooling value if the layer print time is below the threshold" It appears to be more proportional, like "set the fan speed to the maximum speed times the ratio of the layer time divided by the layer threshold time." So, if you set the layer time threshold to 20 seconds and it actually takes 10 seconds, you only get 50% of the maximum cooling level. That suggests that to get anywhere close to 100% cooling, you need to specify a VERY long threshold time, and the algorithm may spend a lot of it's time trying to apply 10, 20 or 30% cooling to longer layers. With my printer, that is as good as off. However, if you use PWM to try to run a 2-wire internal-controller fan below a certain speed, I think you can damage the fan.

This could be very useful, but I need to understand the algorithm better. Also, it would be nice to have a limit in S3D that you can set so it never tries to run a fan slower than its safe minimum.

blackbird2016
Posts: 134
Joined: Wed Aug 02, 2017 1:24 am

Re: Cooling Fan Override for Short Layers Not Working?

Wed Nov 28, 2018 2:24 am

gwhite wrote:
Tue Nov 27, 2018 2:55 pm
...
I'm not quite sure what S3D's algorithm is, but it's definitely NOT " go to maximum cooling value if the layer print time is below the threshold" It appears to be more proportional....
... but I need to understand the algorithm better. Also, it would be nice to have a limit in S3D that you can set so it never tries to run a fan slower than its safe minimum.
As far as I observed the fan speed is distributed over the minimum layer time.
Say you are running the fan at 50% with 100% below 5 seconds layer time,
the additional 50% will be split over the 5 second.
For there never will be a 0-layer-time it never will reach full speed.

Some time ago I provided some post-processing lines to force the fan to full speed
here... viewtopic.php?f=23&t=8890&p=37542#p37542

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