Adding ADXL345 Accelerometer

Connect the Accelerometer to the RPI

Accelerometer 3V3 to RPI pin 17 3.3v

Accelerometer GND to RPI pin 20 Ground

Accelerometer CS to RPI pin 24 GPIO08 (SPI0_CE0_N)

Accelerometer SDO 21 to RPI pin GPIO09 (SPI0_MISO)

Accelerometer SDA to RPI pin 19 GPIO10 (SPI0_MOSI)

Accelerometer SCL 23 to RPI pin GPIO11 (SPI0_SCLK)

There are a number of options you can use to mount the accelerometer. I used this mount

You need to SSH into to your printer and install Numby.

~/klippy-env/bin/pip install -v numpy

sudo apt update

sudo apt install python3-numpy python3-matplotlib -y

Verify Linux SPI driver is enabled

sudo raspi-config

#3 Interface Options > P4 SPI > Yes > OK > Finish

Uncomment the input shaper & resonance tester section in the config.

probe_points: It's recommended to use 1 point in the center of the bed slightly above. I used the same coordinates used when homing Z

Restart klipper with

RESTART

Check to make sure the RPI can communicate with the ADXL345 by running the following command in console

ACCELEROMETER_QUERY

It should return something like:

adxl345 values (x, y, z): -152.983740, 10249.910580, 152.983740

SSH back in to the printer and run the following 2 commands

~/klipper/scripts/calibrate_shaper.py /tmp/resonances_x_*.csv -o /tmp/shaper_calibrate_x.png

~/klipper/scripts/calibrate_shaper.py /tmp/resonances_y_*.csv -o /tmp/shaper_calibrate_y.png

This script will generate the charts /tmp/shaper_calibrate_x.png and /tmp/shaper_calibrate_y.png with frequency responses

You will also get the suggested frequencies for each input shaper, as well as which input shaper is recommended for your setup.

You can see my values for X

You can see my values for Y

With a CoreXY you can also use Klipper to compare belt tension between X and Y. This doesn't tell you if the belts are too tight or too loose. It tells you have the belts are tensioned equally.

Run the following commands in the console

TEST_RESONANCES AXIS=1,1 OUTPUT=raw_data

TEST_RESONANCES AXIS=1,-1 OUTPUT=raw_data

SSH into the pi and run

~/klipper/scripts/graph_accelerometer.py -c /tmp/raw_data_axis*.csv -o /tmp/resonances.png

Based off the generated graph, X had much higher frequencies than Y. I had to tighten the left belt tensioner to to bring the frequencies closer to each other.

As you can see from the 2nd test the frequencies for X and Y are closer together, but could still use a little more adjustment. I think a lot of the frequency variation is due to my cable chain. At lower frequencies it rattles considerably more only when calibrating X.