3.4.0-rc2+2 - PID better but still not perfect

Argo

Hello,

Hardware: Duet 3 Mini5+
Printer and hotend: Voron 2.4 AB-BN-30 mount with Rapido hotend
FW version: 3.4.0-rc2+2 (from here: https://discord.com/channels/@me/909432785540907048/952533190139064360)

With RRF 3.4b6 PID tuning the hotend as a tool, during a print the temperature (set to 215°C) jumped around between 214°C and 220°C.
Hotend PID tuning as heater was fine though.

Did another PID test run with 3.4.0-rc2+2: PID as tool and now temperature jumps around (target temp set to 210°C in this example) between 209.6°C and 210.5°C during print.
PID as heater (no fan involved) is fine again with minimal temperature fluctuation.

PID (as tool) hotend result: M307 H1 R4.779 K0.677:0.184 D3.91 E1.35 S1.00 B0 V24.4

Can anybody else confirm this?

dc42

@argo what exactly is the issue you have now using 2.4.0rc2+2? Is the temperature oscillating in the steady state condition; or only changing when the print cooling fan speed is changed?

Argo

@dc42

At idle / steady state the target temperature is very stable.

The oscillating temperature only happens during a print.
My print profile does use different fan speeds:

80% speed for infill
90% speed for perimeter
100% bridges / overhangs

It has improved with 3.4.0-rc2+2 compared to 3.4b6 from +/- 5°C to about +/- 1°C

Do you need any more data?

jjude

@argo I take advantage of this thread and ask how to do the correct heater and ped PID tuning step by step in version 3.4.0rc2+2 ?

Argo

@jjude

Here you go: https://docs.duet3d.com/en/User_manual/Connecting_hardware/Heaters_tuning

gloomyandy

@argo So are you saying that if you just tune the heater (rather than a tool), then when printing the same part your temperature is even more stable than the +/-1 degree that you get with tuning the tool and using rc2+2?

dc42

@argo it's usual for the temperature to change temporarily when the print speed changes, because of the cooling effect of the fan on the nozzle. If it is working well then the fan feedforward implemented in RRF will reduce those temperature changes.

You can check whether the feedforward is helping by setting the second K parameter in the M307 command to zero. This will disable feedforward.

Argo

@gloomyandy

Correct. PID tuned as a heater the variance is +/- 0.2°C at max which is pretty good.
So PID tuning as a heater works for me but I suspect it's not how the feature "PID as tool" is intended to be.

About my Hotend:
The Rapido is quite isolated and the fan shroud is optimised with simulations etc. (not by me). So there is not much fan hitting the nozzle.

@dc42
Second K value = zero is the same as PID tuning the hotend as a heater and not as a tool? Then see my response to gloomyandy. That works quite well.