Extruder Temp Swings

helping you get the most out of your RigidBot extruder

Extruder Temp Swings

Postby Klantz » 05 Aug 2014, 03:14

Trying to get this forum going as G+ drives me crazy when posts get buried and lost.

I was just wondering if anyone else has had large swings in temp when printing. If I set the temp to be 210 in Cura, it will swing 5-10* in either direction creating a wave effect of heating and cooling. Generally hasn't been a problem but I would like it to cycle much sooner than a 5* drop and cut off before 5 over. I'm not too familiar with tweaking the firmware but not against it, I just don't really know what I'm doing on that end.
Klantz
 
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Re: Extruder Temp Swings

Postby Faye » 05 Aug 2014, 07:31

1) check that you cannot see the labels on your fans, and that they are sucking air in (blowing over the heatsink). If you don't do this, then you will likely have a PID autotune fail on you.

2) run a PID autotune:
You'll need a serial terminal, a simple one is fine. If you have a computer running Python, you should be able to install pyserial with: easy_install pyserial
Once you have that installed you can run miniterm.py -e <port> 115200
Port is your serial port. For my Mac, that's /dev/tty.usbmodem1411
When you do this, your printer will say hello.
I use the LCD to move the Z axis up about 100mm and the X axis along about 60mm, just to keep the extruder away from anything.
You can then send it the command to auto tune:
M303 E0 S200 C8
The S200 is the temperature to cycle around. If you are at all unsure, use a lower value. It can overshoot on a misconfiguration by up to 20C before it stops, if you are aiming at ABS temperatures then you could start to melt your insulators.
It should cycle up to temperature, maybe overshoot a little, go under, heat back up etc. 8 times.
At the end it will spit out the P I and D values:

ok T:200.56 @:0
bias: 119 d: 119 min: 194.69 max: 205.63
Ku: 27.71 Tu: 48.89
Clasic PID
Kp: 16.62
Ki: 0.68
Kd: 101.59
For example (your materials may cause different numbers to appear, use what you get)
Type the following:
M301 P16.62 I0.68 D101.59
and it should echo those values back to you.
type the following to save the setting:
M500
It should tell you it saved the settings.

Now check the setting:

M104 E0 S200

Will heat the bot up to 200. Rather than continually fluctuating however, it should very quickly settle at a steady state.

M104 E0 S0

Will turn the heating off. It will take some time to cool back down to 0.
Last edited by Faye on 06 Aug 2014, 16:23, edited 3 times in total.
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Re: Extruder Temp Swings

Postby spiderdaddy » 05 Aug 2014, 10:07

Hi, thanks for this description of PID tuning. It's great to get these posts on the forum, because they get lost so easily on g+.

Would it be possible for you to add this to the Wiki page on PID tuning?

Also, if you are using Prontrface, or Octoprint you get a 'command' line where you can type the gcode directly.
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Re: Extruder Temp Swings

Postby Klantz » 05 Aug 2014, 13:17

That's fantastic, thanks! I know I'm really trying to get this forum thing going.
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Re: Extruder Temp Swings

Postby Klantz » 05 Aug 2014, 21:01

I am getting this response when I try and do the PID auto-tune

ok
M303 E0 S180 C8
PID Autotune start
ok T:131.94 @:128
ok T:131.72 @:128
ok T:131.77 @:128
ok T:132.26 @:128
ok T:133.20 @:128
ok T:134.55 @:128
ok T:136.61 @:128
ok T:139.33 @:128
ok T:142.48 @:128
ok T:146.11 @:128
ok T:150.53 @:128
ok T:156.10 @:128
ok T:162.45 @:128
ok T:169.81 @:128
ok T:179.33 @:128
ok T:190.65 @:0
PID Autotune failed! Temperature to high
ok
Error:0
: Extruder switched off. MAXTEMP triggered !
Error:Printer stopped due to errors. Fix the error and use M999 to restart. (Temperature is reset. Set it after restarting)


I can print fine but I get pretty big temp swings. Any ideas?
Klantz
 
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Re: Extruder Temp Swings

Postby Faye » 06 Aug 2014, 00:45

Klantz wrote:I am getting this response when I try and do the PID auto-tune
ok T:190.65 @:0
PID Autotune failed! Temperature to high
ok

I can print fine but I get pretty big temp swings. Any ideas?


Did you have the fans blowing on the heatsink? Or are they blowing toward your hand when you put your hand over the fan?
I changed that, plus I reseated my thermistor so that the cable ran up the heatsink and it stopped overheating crazily.
Also the fan should be plugged into Fan 2 and always on.


Faye
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Re: Extruder Temp Swings

Postby Klantz » 06 Aug 2014, 03:50

It was the PID settings. I ran the auto-tune and got these values:

P 12.74
I 0.45
D 90.14

Now it's dead flat on holding a temp.
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Re: Extruder Temp Swings

Postby Faye » 06 Aug 2014, 16:22

Only now do I notice that your autotune didn't start from room temperature.
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Re: Extruder Temp Swings

Postby Klantz » 06 Aug 2014, 22:55

Faye wrote:Only now do I notice that your autotune didn't start from room temperature.


Yeah it was very odd. It makes a huge difference in the serial terminal used. I was getting the errors when using Termite or just a standard serial terminal. I switched over to pronterface and used that terminal and it worked fine. So bizarre. everything looks good now though.
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Re: Extruder Temp Swings

Postby greg » 07 Aug 2014, 12:49

Sorry I didn't see this conversation going on. We've been crowd sourcing PID values on G+ (https://plus.google.com/109203428893215 ... 5TFp5S6Cdy) and have some better default values and an explanation for the temp swings. The RigidBoard controller is flashed with firmware that has PID tuning for the original smaller hot end. The replacement hot end needs values closer to what you've found here. The data is shared here: https://docs.google.com/spreadsheets/d/ ... sp=sharing and the write up in the wiki is here: http://rigidtalk.com/wiki/index.php?title=PID_tuning

Viva la forums!
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