I just thought I'd post a few observations I've noticed for PID tuning the heated nozzel
From what I understand the duet boards use a different mechanism for PID tuning, controlling the heaters such as the nozzel that's supposed to be more accurate.
I suspect / guess it's also true that the ADC on the Arm chip probably has a higher resolution than the one on a 16bit board for measuring the existing temperature.
When running the PID for the hotend typically it's a case of
M303 H1 P0.7 S205
- H1 - Heater 1
- P0.7 - PMW Power rating to use (0 - 1)
- S205 - target temperature
One critical thing appears to be the power rating.
- If it's set too high such as 1, then you could end up with a thermal runaway which causes the hotend to shoot off to the moon
- If it's set too low then then the hotend will take a long time to heat up and may not be able to keep up with the target temperature
- I've also noticed that the higher the value more pronounced the oscillations
Initially I started with a power rating of around 0.5
This works while the printer isn't printing, but as soon as I started printing PETG (barely no fan) at around 230
it couldn't keep up and stopped the printer after the temperature dropped too low, so I redid the PID tuning with 0.6
Then I tried printing with PLA at 205, and a 3hole fan duct I'd just printed off
This couldn't keep up while printing and would drop too low (probably due to the increased fan cooling the nozzel)
so I redid the PID with a factor of 0.7
It seems to be working okay, but it seems to oscillate different amounts based on the type of operation
at around 20% infill half way through the print it seems to
slowly climb to 205 then suddenly dip to around 202 / 203 before climbing again
- Since the extrusion and the fan are drawing heat away from the nozzel, a static PID test might indicate everything is fine but might actually be underpowered.
- Any oscillations you might see during heating the nozzel while not printing, might actually smooth out somewhat while printing due to the plastic taking heat away
During printing I've noticed the following influences the amount of power needed
- The speed of printing (faster extrusion means more heat being taken away from the nozzel)
- If a fan is in use (increased cooling = more power)
- If your using a 3 nozzel fan duct (increased cooling = more power)
- The type of print operation such as solid infill, or partial infill (solid infill = more plastic extruded / more power needed)
I should mention this isn't a criticism, but just something to watch out for when setting up a printer.
Initially I was setting the power rating as low as possible to avoid oscillations
but since those kinda smooth out a bit during printing, I've now realised it needs to be on the higher end to keep up with the printing and the fan.
below are a couple of screengrabs of the temperature graph while printing pla at 205