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Load Cells

This page covers installing SimpleAF using the strain gauges (load cells) already built into the bed of your printer as the probe. There is no extra probe hardware to buy or mount, the nozzle taps the bed and the bed load cells detect the contact.

Looking for Load Cells for Z-Offset? See Load Cells for Z-Offset.

Experimental High risk of bed or toolhead damage

Load cell probing is EXTREMELY EXPERIMENTAL. The nozzle is pushed onto the bed with a force measured by the load cells, if the load cells are not calibrated properly or something else goes wrong you can damage your printer. Be ready to hit the e-stop button in your UI or Grumpyscreen, or the power button, and never leave your printer unattended while homing, probing or bed meshing.

Kalico only

Load cell probing REQUIRES Kalico. The installer will automatically setup kalico for a install or reinstall or if you switch to loadcells from an existing installation.

New here? See Getting Started.

Supported Printers

Printer Status
Ender 3 V3 Tested
K1 Tested
K1C Configured, not tested
K1 SE Configured, not tested
K1 Max Tested

Any other printer is not supported, this includes the Ender 3 V3 KE, Ender 5 Max, CR10SE, Nebula Pad.

The Ender 3 V3 keeps using its physical endstop for homing Z, the load cells are used for probing and bed meshing.

Note

The load cell probe reads all four bed load cells together as a single probe, this needs new MCU firmware which the installer takes care of.

Overview

  1. Install with the loadcells probe
  2. Power cycle the printer so the new MCU firmware is applied
  3. Calibrate the load cells with a known weight
  4. Test the probe and check its accuracy
  5. Run a bed mesh
  6. Do PID tuning and input shaping
  7. Configure Nozzle Wipe - currently this must be done manually, we are exploring integrating a default nozzle wipe for load cells soon.

Installation

Warning

The installation can only be performed on a printer which has been rooted and ssh granted, and you need root access, if you are not already root, then follow the Enable Root Access instructions.

If you've installed Guilouz's Helper Script, or installed Fluidd or Mainsail through any other means (such as from Creality directly), you need to factory reset before continuing.

Clone the Repo

git config --global http.sslVerify false
git clone https://github.com/pellcorp/creality.git /usr/data/pellcorp

Note

If you had already cloned the pellcorp creality repository before being asked to factory reset, the git repo is still there and you can skip the cloning step!

Run the installer

/usr/data/pellcorp/installer.sh --install loadcells

Post Installation

MCU Firmware updates are pending

At the end of the installer process if you get this message:

WARNING: MCU Firmware updates are pending you need to power cycle your printer!

It means that new MCU firmware updates need to be applied and this can only be done by power cycling the printer. After your printer is power cycled you can verify firmware was updated with the CHECK_FIRMWARE macro from Fluidd or Mainsail, if you see this message:

INFO: Your MCU Firmware is up to date!

Your printer MCU firmware was updated successfully. If you still see the MCU Firmware updates are pending you need to power cycle your printer! message after a power cycle, check the /tmp/mcu_update.log, you may be asked to provide this file on Discord if you need additional assistance, sometimes an additional power cycle can solve the problem, there is a very short window of time (15 seconds) in which the MCU firmware can be updated, so there is a chance it will work after an additional power cycle.

Calibration

Warning

The load cells must be calibrated before you can probe with them, until you do the printer will stop with Load Cell Probe Error: Load Cell not calibrated. Never guess the calibration value, the safety limits are all in grams and an inaccurate calibration lets the nozzle push far harder than you intend.

Check the Load Cells

Make sure the bed is empty and run LOAD_CELL_DIAGNOSTIC, it collects samples for 10 seconds, press on the bed while it runs.

  • Saturated samples should be 0
  • Unique values should be a large part of the samples collected, if it is 1 there is a wiring or configuration problem
  • Sample range should increase when you press on the bed

Source: https://github.com/KalicoCrew/kalico/blob/main/docs/Load_Cell.md#diagnostics

Calibrate the Load Cells

You need an object of known weight, weigh it on a kitchen scale.

Tip

On the Ender 3 V3 a known weight of ~3 kg (around 3000 grams) was needed during testing,

On the K1 a known weight of ~6 kg (around 6000 grams) was needed during testing,

a lighter weight fails with the Tare and Calibration readings are less than 1% different! error, see Calibration Errors.

New spools of filament work well, a brand new spool is typically 1000 g of filament plus the spool itself, which is about 250 g for a bamboo plastic spool or about 175 g for a cardboard spool. Weight whatever you use on a kitchen scale and enter the real weight.

  1. Remove everything from the bed
  2. Run LOAD_CELL_CALIBRATE
  3. Run TARE
  4. Place your object of known weight in the centre of the bed
  5. Run CALIBRATE GRAMS=<weight in grams> for example CALIBRATE GRAMS=3000
  6. Run ACCEPT
    Upon completion SAVE_CONFIG

You can use ABORT to cancel at any time. Afterwards run LOAD_CELL_DIAGNOSTIC again, and LOAD_CELL_READ will it will report the force on the bed in grams.

Source: https://github.com/KalicoCrew/kalico/blob/main/docs/Load_Cell.md#calibration

Calibration Errors

Error Cause Fix
Tare and Calibration readings are less than 1% different! The weight is too light, the reading has to change by at least 1% of the sensor range Use more weight, on the Ender 3 V3 about 3 kg (3000 grams) is needed and 2598 grams was not enough. The message suggests a higher gain, but gain is already at its highest setting (A-128), so more weight is the only fix
Sensor is saturated with too much load! The weight is too heavy Use less weight
Tare and Calibration readings are the same! The reading did not change Check the weight is actually on the bed and run LOAD_CELL_DIAGNOSTIC to check the sensor

The calibration is still active after one of these errors, so you can change the weight and run CALIBRATE GRAMS=<weight in grams> again.

Test the Probe

Run LOAD_CELL_TEST_TAP, then gently tap the nozzle or press on the bed 3 times, it will report each tap as it is detected. If no tap is detected within 30 seconds it fails.

Note

Load cell probes always report not triggered for QUERY_ENDSTOPS and QUERY_PROBE, use LOAD_CELL_TEST_TAP instead.

Probe Accuracy

Make sure the nozzle is clean and there is no filament oozing from it, and if you are heating the nozzle keep it around 140°C, ooze on the nozzle is the biggest source of bad taps.

  1. Home All (G28)
  2. Make sure the nozzle is centred on the bed
  3. Run PROBE_ACCURACY

Bed Mesh

  1. Home All (G28)
  2. Make sure the nozzle is clean
  3. Run BED_MESH_CALIBRATE
    Upon completion SAVE_CONFIG

Watch the first bed mesh, the nozzle taps the bed at each point.

Pid Tuning and Input Shaping

At least PID tuning (bed and extruder) and input shaping is required for acceptable printing. If you try and print before any calibration you will most likely have poor quality.

Note

You can use the QUICK_START Macro to complete Bed and Nozzle PID Tuning and Input Shaping Automatically.

Pid Tuning

Source: Calibrate Pid Settings

For example you might run these:

PID_CALIBRATE_BED BED_TEMP=65
PID_CALIBRATE_HOTEND HOTEND_TEMP=230

Note

The PID_CALIBRATE_BED and PID_CALIBRATE_HOTEND macros are located in the useful_macros.cfg file and they have defaults values for BED_TEMP and HOTEND_TEMP so you can just run them by clicking on them if you want that same temperature.

Input Shaping

There is no default configuration for input shaping so it is essentially disabled out of the box.

You can use the SHAPER_CALIBRATE macro to run input shaping, just be sure to SAVE CONFIG at the end, to choose the automatically selected shaper config, be aware though that the shaper chosen might be sub-optimal due to a slight difference in vibrations between two options. So you should probably review the output and potentially choose an alternative if it gives you higher recommended max acceleration for minimal increase in vibration.

Input Shaper Auto Calibration

Tuning

The load cell probe settings are in the [load_cell_probe] section of loadcells.cfg, which you can edit from the config editor in Fluidd or Mainsail.

Tap Failures

If you see tap validation errors in the console like TAP_PULLBACK_TOO_SHORT or TAP_BREAK_CONTACT_TOO_LATE the pullback move is too short, increase pullback_distance in the [load_cell_probe] section. The default is 0.2, on the Ender 3 V3 setting it to 0.5 fixed frequent TAP_PULLBACK_TOO_SHORT failures.

[load_cell_probe]
pullback_distance: 0.5

If the errors are TAP_BREAK_CONTACT_TOO_EARLY it is too long.

Trigger Force

trigger_force is the force in grams that triggers the probe, it is set by the mount, 75 for the Ender 3 V3 and 160 for the K1 and K1 Max. Probing always overshoots this, so raise it in small steps only if you need to.

Safety Limits

  • force_safety_limit (default 2000 grams) is the most force allowed on the bed before a probe move starts. If it is exceeded you get force of 3000g exceeds force_safety_limit (2000g) before probing!, this can be caused by the nozzle already resting on the bed or something pushing on the bed.
  • drift_safety_limit (default 1000 grams) is the most force allowed while probing before it triggers. If it is exceeded you get force exceeded drift_safety_limit before triggering!.

Switching Back

To go back to a different probe see Switching Probes.

Warning

Do not switch to Klipper while loadcells is still your probe, Klipper does not support the load cell probe and will not start correctly. Switch to a different probe first, and then if you want to go back to Klipper run:

~/pellcorp/installer.sh --klipper

First Print

You might need to optimise your load cell z offset using baby stepping.

In fluidd the save button after you finish or cancel your print can be a bit hard to find, look for

image

Other Calibrations

Info

The default value for pressure advance is set to 0.04

Refer to Orcaslicer Calibration for more calibrations

Refer to the Ellis Print Tuning Guide for more great tuning ideas.

Where can I get help?

For support, join the SimpleAF Discord.