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klipper-dgus/docs/FAQ.md

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Frequently asked questions

  1. How do I calculate the step_distance parameter in the printer config file?
  2. Where's my serial port?
  3. The "make flash" command doesn't work
  4. How do I change the serial baud rate?
  5. Can I run Klipper on something other than a Raspberry Pi 3?
  6. Why can't I move the stepper before homing the printer?
  7. Why is the Z position_endstop set to 0.5 in the default configs?
  8. I converted my config from Marlin and the X/Y axes work fine, but I just get a screeching noise when homing the Z axis
  9. When I set "restart_method=command" my AVR device just hangs on a restart
  10. Will the heaters be left on if the Raspberry Pi crashes?
  11. How do I upgrade to the latest software?

How do I calculate the step_distance parameter in the printer config file?

If you know the steps per millimeter for the axis then use a calculator to divide 1.0 by steps_per_mm. Then round this number to six decimal places and place it in the config (six decimal places is nano-meter precision).

The step_distance defines the distance that the axis will travel on each motor driver pulse. It can also be calculated from the axis pitch, motor step angle, and driver microstepping. If unsure, do a web search for "calculate steps per mm" to find an online calculator.

Where's my serial port?

The general way to find a USB serial port is to run ls -l /dev/serial/by-id/ from an ssh terminal on the host machine. It will likely produce output similar to the following:

lrwxrwxrwx 1 root root 13 Jan 3 22:15 usb-UltiMachine__ultimachine.com__RAMBo_12345678912345678912-if00 -> ../../ttyACM0

The name found in the above command is stable and it is possible to use it in the config file and while flashing the micro-controller code. For example, a flash command might look similar to:

sudo service klipper stop
make flash FLASH_DEVICE=/dev/serial/by-id/usb-UltiMachine__ultimachine.com__RAMBo_12345678912345678912-if00
sudo service klipper start

and the updated config might look like:

[mcu]
serial: /dev/serial/by-id/usb-UltiMachine__ultimachine.com__RAMBo_12345678912345678912-if00

Be sure to copy-and-paste the name from the "ls" command that you ran above as the name will be different for each printer.

The "make flash" command doesn't work

The code attempts to flash the device using the most common method for each platform. Unfortunately, there is a lot of variance in flashing methods, so the "make flash" command may not work on all boards.

If you're having an intermittent failure or you do have a standard setup, then double check that Klipper isn't running when flashing (sudo service klipper stop), make sure OctoPrint isn't trying to connect directly to the device (open the Connection tab in the web page and click Disconnect if the Serial Port is set to the device), and make sure FLASH_DEVICE is set correctly for your board (see the question above).

However, if "make flash" just doesn't work for your board, then you will need to manually flash. See if there is a config file in the config directory with specific instructions for flashing the device. Also, check the board manufacturer's documentation to see if it describes how to flash the device. Finally, on AVR devices, it may be possible to manually flash the device using avrdude with custom command-line parameters - see the avrdude documentation for further information.

How do I change the serial baud rate?

The default baud rate is 250000 in both the Klipper micro-controller configuration and in the Klipper host software. This works on almost all micro-controllers and it is the recommended setting. (Most online guides that refer to a baud rate of 115200 are outdated.)

If you need to change the baud rate, then the new rate will need to be configured in the micro-controller (during make menuconfig) and that updated code will need to be flashed to the micro-controller. The Klipper printer.cfg file will also need to be updated to match that baud rate (see the example.cfg file for details). For example:

[mcu]
baud: 250000

The baud rate shown on the OctoPrint web page has no impact on the internal Klipper micro-controller baud rate. Always set the OctoPrint baud rate to 250000 when using Klipper.

Can I run Klipper on something other than a Raspberry Pi 3?

The recommended hardware is a Raspberry Pi 2 or a Raspberry Pi 3.

Klipper will run on a Raspberry Pi 1 and on the Raspberry Pi Zero, but these boards don't have enough processing power to run OctoPrint well. It's not uncommon for print stalls to occur on these slower machines (the printer may move faster than OctoPrint can send movement commands) when printing directly from OctoPrint. If you wish to run on one one of these slower boards anyway, consider using the "virtual_sdcard" feature (see config/example-extras.cfg for details) when printing.

For running on the Beaglebone, see the Beaglebone specific installation instructions.

Klipper has been run on other machines. The Klipper host software only requires Python running on a Linux (or similar) computer. However, if you wish to run it on a different machine you will need Linux admin knowledge to install the system prerequisites for that particular machine. See the install-octopi.sh script for further information on the necessary Linux admin steps.

Why can't I move the stepper before homing the printer?

The code does this to reduce the chance of accidentally commanding the head into the bed or a wall. Once the printer is homed the software attempts to verify each move is within the position_min/max defined in the config file. If the motors are disabled (via an M84 or M18 command) then the motors will need to be homed again prior to movement.

If you want to move the head after canceling a print via OctoPrint, consider changing the OctoPrint cancel sequence to do that for you. It's configured in OctoPrint via a web browser under: Settings->GCODE Scripts

If you want to move the head after a print finishes, consider adding the desired movement to the "custom g-code" section of your slicer.

Why is the Z position_endstop set to 0.5 in the default configs?

For cartesian style printers the Z position_endstop specifies how far the nozzle is from the bed when the endstop triggers. If possible, it is recommended to use a Z-max endstop and home away from the bed (as this reduces the potential for bed collisions). However, if one must home towards the bed then it is recommended to position the endstop so it triggers when the nozzle is still a small distance away from the bed. This way, when homing the axis, it will stop before the nozzle touches the bed.

Almost all mechanical switches can still move a small distance (eg, 0.5mm) after they are triggered. So, for example, if the position_endstop is set to 0.5mm then one may still command the printer to move to Z0.2. The position_min config setting (which defaults to 0) is used to specify the minimum Z position one may command the printer to move to.

Note, the Z position_endstop specifies the distance from the nozzle to the bed when the nozzle and bed (if applicable) are hot. It is typical for thermal expansion to cause nozzle expansion of around .1mm, which is also the typical thickness of a sheet of printer paper. Thus, it is common to use the "paper test" to confirm calibration of the Z height - check that the bed and nozzle are at room temperature, check that there is no plastic on the head or bed, home the printer, place a piece of paper between the nozzle and bed, and repeatedly command the head to move closer to the bed checking each time if you feel a small amount of friction when sliding the paper between bed and nozzle - if all is calibrated well a small amount of friction would be felt when the height is at Z0.

I converted my config from Marlin and the X/Y axes work fine, but I just get a screeching noise when homing the Z axis

Short answer: Try reducing the max_z_velocity setting in the printer config. Also, if the Z stepper is moving in the wrong direction, try inverting the dir_pin setting in the config (eg, "dir_pin: !xyz" instead of "dir_pin: xyz").

Long answer: In practice Marlin can typically only step at a rate of around 10000 steps per second. If it is requested to move at a speed that would require a higher step rate then Marlin will generally just step as fast as it can. Klipper is able to achieve much higher step rates, but the stepper motor may not have sufficient torque to move at a higher speed. So, for a Z axis with a very precise step_distance the actual obtainable max_z_velocity may be smaller than what is configured in Marlin.

When I set "restart_method=command" my AVR device just hangs on a restart

Some old versions of the AVR bootloader have a known bug in watchdog event handling. This typically manifests when the printer.cfg file has restart_method set to "command". When the bug occurs, the AVR device will be unresponsive until power is removed and reapplied to the device (the power or status LEDs may also blink repeatedly until the power is removed).

The workaround is to use a restart_method other than "command" or to flash an updated bootloader to the AVR device. Flashing a new bootloader is a one time step that typically requires an external programmer - search the web to find the instructions for your particular device.

Will the heaters be left on if the Raspberry Pi crashes?

The software has been designed to prevent that. Once the host enables a heater, the host software needs to confirm that enablement every 5 seconds. If the micro-controller does not receive a confirmation every 5 seconds it goes into a "shutdown" state which is designed to turn off all heaters and stepper motors.

See the "config_digital_out" command in the MCU commands document for further details.

How do I upgrade to the latest software?

The general way to upgrade is to ssh into the Raspberry Pi and run:

cd ~/klipper
git pull
~/klipper/scripts/install-octopi.sh

Then one can recompile and flash the micro-controller code. For example:

sudo service klipper stop
make flash FLASH_DEVICE=/dev/ttyACM0
sudo service klipper start

However, it's often the case that only the host software changes. In this case, one can update and restart just the host software with:

cd ~/klipper
git pull
sudo service klipper restart

If after using this shortcut the software warns about needing to reflash the micro-controller or some other unusual error occurs, then follow the full upgrade steps outlined above. Note that the RESTART and FIRMWARE_RESTART g-code commands do not load new software - the above "sudo service klipper restart" and "make flash" commands are needed for a software change to take effect.