Feature Request - Regular Fan Speed At Time

[Kumpu 1]

Right now you can set a layer/height for this, but I would like to be able to set a time. Marlin will hault my printer with a thermal runaway error when the fans ramp up too quickly, because obviously the nozzle gets cooled as well. So having a fixed ramp up time option would make a lot of sense to me. Each print/settings change has different layer times and I have to decide everytime if setting it to layer n is slow enough.

 

I'm not sure if gcode allows you to measure time, but it wouldn't have to be that accurate - repeatability is way more important. I just want to be able to find a value that will work reliably.

[AirBronto 8]

This sounds a bit like an X-Y problem.  First off, your cooling fan should be angled in a way that it doesn't cool the nozzle very much.  The cool air should hit right below the nozzle (so the brunt of the cooling effect hits the extruded filament).  I would check to make sure it's angled properly.

 

Also, if you're running marlin, I think it would make more sense to change your thermal runaway parameters.  Really it would be as simple as updating the following settings in Configuration_adv.h:

 

If you're getting this issue after you hit your print temperature but before you change temperature during a print:

THERMAL_PROTECTION_PERIOD
THERMAL_PROTECTION_HYSTERESIS

If you're getting this after you change temperature mid-print:

WATCH_TEMP_PERIOD
WATCH_TEMP_INCREASE

 

For me, I had to update my protection_period and hysteresis because I am running a larger nozzle so I push more material than my printer was originally designed for.  I was regularly getting thermal runaways because the hotend was cooling down faster than my PIDs were expecting, and while they would eventually catch up, by that point it was too late and the thermal protection was triggered.  I set my THERMAL_PROTECTION_PERIOD to 80 seconds, and my THERMAL_PROTECTION_HYSTERESIS to 3 degrees.  I haven't had any thermal runaway issues since then.

[Kumpu 1]

On 1/21/2019 at 8:52 PM, AirBronto said:

This sounds a bit like an X-Y problem.  First off, your cooling fan should be angled in a way that it doesn't cool the nozzle very much.  The cool air should hit right below the nozzle (so the brunt of the cooling effect hits the extruded filament).  I would check to make sure it's angled properly.

I guess you're right, I didn't pay much attention to that when designing the fan ducts. Definitely room for improvement there.

 

During the first layer the fans are off, but soon after layer 2 starts and the fans begin blasting, I get that error. Should I change the first two constants you mentioned then? Also I'm a bit unsure about messing with marlin. I only flashed it once for reasons I don't remember but I know that the usb connection was very unstable, and I was glad it even worked and didn't brick my board or anything. I mean if that's what I have to do I'll give it a go but I still think it would be a good feature for cura to have.

[AirBronto 8]

Can you post a picture of your temperature graph when the thermal runaway happens?  I want to see if it looks like your heater is eventually going to get your nozzle to the right temp and your thermal runaway protection is just too aggressive, or if it looks like your fan is just overpowering your heater.

 

Definitely check the airflow and the design of your duct, the air shouldn't be hitting/cooling the nozzle at all, it should only be hitting the freshly extruded material.  In reality the turbulence from the duct will cause the nozzle to lose some heat, but it should be minimal.  I can crank my fan up to 100% and my nozzle loses about 1 degree.

 

Have you done a PID tune with Marlin yet?  That can be another thing that could help, it could be that your firmware just doesn't have a good handle on how much power it takes to heat up your nozzle, and when the fan kicks on it gets knocked out of whack and can't keep up.  A temperature graph screenshot would help troubleshoot that as well.

[Kumpu 1]

No idea how I'd graph my temperature, I don't use octoprint or anything. Can marlin log that on the sd card? In any case, the heater can definitely keep up if the fan curve isn't too agressive. It's just on small prints that this happens, as layer times shrink and therefore "Regular Fan Speed at Layer" results in a steeper fan curve over time. I saw temps drop by almost 20° C and I think at that point that's fair for marlin to step in. Sometimes when I forget to increase that setting I sit there and dial back the fans manually to help things out. Annoying.

PID tuning should help a lot, I mean if it cranked up the power more quickly it wouldn't be an issue. Well I guess except if it's close to the power limit anyway.

 

I'll redesign my ducts and I expect that to fix my problems. But if not I'll look into PID tuning as you suggested.

[AirBronto 8]

If you only print via SD then you probably don't have a graph of temperature data.  Octoprint is super useful for stuff like that but if you don't have a raspberry pi then I guess you're out of luck.

 

20* drop when the fan comes on is way way way too much.  Either your PIDs are incredibly fragile and even a tiny increase in airflow messes them up, or your fan duct is very wrong.  Once you get a new duct on there I think your problem will just disappear.

 

Some people recommend doing PID tuning at 50% fan, that way your PIDs are a little more aggressive than needs be with no fan, but they can handle more airflow without getting bogged down.

[Kumpu 1]

50 minutes ago, AirBronto said:

20* drop when the fan comes on is way way way too much.  Either your PIDs are incredibly fragile and even a tiny increase in airflow messes them up, or your fan duct is very wrong.  Once you get a new duct on there I think your problem will just disappear.

 

Yes, the fans blast the nozzle dead on. Iirc I made it so the middle of the air stream would more or less hit the end of it, thinking that'd give me best performance or something...

To my defense I can say this was one of my very first projects, never did CAD before and I just wanted something that worked.

[Kumpu 1]

Hi, I just wanted to come back and tell you that it's fixed now. I printed new ducts which made it much better, where before it was up to 15-20° C drop at maybe 50-60% fan speed, with the new part it's more like 8-10° drop at 100% and fast recovery. Then I also did the PID tuning (at 50% fan speed), it overshoots more and oscillates a bit with no fans, but recovery is in a matter of seconds, drop is reduced and with fans on it's very stable.

So all in all a good result. Thank you for your help.

Edited January 25, 2019 by Kumpu

[AirBronto 8]

Awesome, glad it you got it all figured out!