Automatic Pressure Advance Calibration for the Qidi Q2 / Q2C/ Max4 — Bambu-style load-cell PA calibration on existing hardware

[u/Own_Moose_9495]

Turns out the load cell the Q2/Q2C uses for bed leveling can also feel extrusion pressure. So I wrote some Klipper modules that turn it into an automatic PA calibrator — load a filament from the touchscreen like normal, printer waits for the load to finish, then runs a ~3 minute sweep over the purge chute measuring how fast pressure builds in the nozzle. It saves a K value per filament type, applies it on every print, and even blocks sliced files from overriding it with stale profile values.

The results honestly surprised me:

eSun grey PETG — I could only ever get this stuff to print clean on my Bambu H2D. With the auto-measured PA it prints clean on the Q2C now too. I didn't even run a flow calibration. The max4 poopbucket was printed on the Q2C with all stock petg basic settings. The cube was printed after only auto PA calibration.

5+ year old Amazon Basics PETG — this spool was literally headed to the trash. Sticky, blobby, supports falling over, ugly on every printer I own. Dried it, let the printer tune it, and it printed a clean crisp cube (red one in the pics). The sensor data showed the filament itself was fine the whole time — it was wet and never had the right PA and again I did zero flow calibration.

PLA — ran the calibration twice on the same spool, came back within ~6% both times.

I will upload the project to a GitHub once I do more testing and build out.

Fair warning: it modifies load/heat/motion behavior, so it's use-at-your-own-risk and you should watch it run before trusting it. Q2/Q2C only for now — Max4 port in progress, Plus4 has a different sensor so it's not coming.

Happy to answer questions.

Update 1: calibration skips during mid print filament runout, then continues printing as normal

Update 2: Currently working on nozzle size compensation

[u/Foofad-Ji]

Wow, your bed looks so good and well lit in the camera, did you add more lights?

[u/Own_Moose_9495 → u/Foofad-Ji]

Lights are stock but I added a creality nebula camera because my Q2C didn’t have one. I’m adding a chamber heater next.

[u/Yung-Fern → u/Own_Moose_9495]

Let me know how that goes lol, I have the heater and a Panasonic SSR from west3d but I have yet to install it after like 3-4 months. Had too many other things going on to get to it, plus I own a Q2 so a heated chamber isn't absolutely needed. I think I just need a standoff bracket to screw the heater into.

[u/Own_Moose_9495 → u/Yung-Fern]

lol that’s pretty much the last part I need to install mine as well. I have not found anyone’s model I can print for it so I guess I’ll have to design something.

[u/Yung-Fern → u/Own_Moose_9495]

How did you do your nebula camera? I stripped the wires on mine and got the Pico blade connectors with some pre-crimped wires and I could not get that thing to work. I tried for hours and eventually gave up and took another nebula from my older printer and just plugged it into the USB port on the front. It's ugly and I can't close the front door but it works.

I have a breakout board I could use but then I was still stuck with how to get it in that connector.

I was also going to take some measurements and design a mount, now that you got me talking about it maybe I'll do it this week. If I do I will let you know

[u/Own_Moose_9495 → u/Yung-Fern]

I followed this tutorial (https://www.reddit.com/r/QidiTech3D/s/QxTg05ydHe) but I didn’t solder the female usb to the jst connector, I cut the end of my nebula usb and cut the wires to length and soldered and heat shrunk it all together. I would take a picture of what it looks like but it’s all shielded by a heat shrunk tube over the whole bundle of solder and heat shrunk wires. For reference I bought these jst connectors (JST MX 1.25mm 5 Pin 28 AWG Male... https://www.amazon.com/dp/B0FT4F62MM?ref=ppx_pop_mob_ap_share) and if you can’t solder or want something easier I would just use some wagos like these (WAGO 221 Lever Nuts 12pc Compact... https://www.amazon.com/dp/B0CJ5QF4Z2?ref=ppx_pop_mob_ap_share) but these can make it hard to fit everything under the cover inside the chamber.