231 lines
9.3 KiB
Markdown
231 lines
9.3 KiB
Markdown
This document describes Klipper's automatic calibration system for
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"delta" style printers.
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Delta calibration involves finding the tower endstop positions, tower
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angles, delta radius, and delta arm lengths. These settings control
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printer motion on a delta printer. Each one of these parameters has a
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non-obvious and non-linear impact and it is difficult to calibrate
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them manually. In contrast, the software calibration code can provide
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excellent results with just a few minutes of time. No special probing
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hardware is necessary.
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Ultimately, the delta calibration is dependent on the precision of the
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tower endstop switches. If one is using Trinamic stepper motor drivers
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then consider enabling [endstop phase](Endstop_Phase.md) detection to
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improve the accuracy of those switches.
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Automatic vs manual probing
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===========================
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Klipper supports calibrating the delta parameters via a manual probing
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method or via an automatic Z probe.
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A number of delta printer kits come with automatic Z probes that are
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not sufficiently accurate (specifically, small differences in arm
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length can cause effector tilt which can skew an automatic probe). If
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using an automatic probe then first
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[calibrate the probe](Probe_Calibrate.md) and then check for a
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[probe location bias](Probe_Calibrate.md#location-bias-check). If the
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automatic probe has a bias of more than 25 microns (.025mm) then use
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manual probing instead. Manual probing only takes a few minutes and it
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eliminates error introduced by the probe.
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Basic delta calibration
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=======================
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Klipper has a DELTA_CALIBRATE command that can perform basic delta
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calibration. This command probes seven different points on the bed and
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calculates new values for the tower angles, tower endstops, and delta
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radius.
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In order to perform this calibration the initial delta parameters (arm
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lengths, radius, and endstop positions) must be provided and they
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should have an accuracy to within a few millimeters. Most delta
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printer kits will provide these parameters - configure the printer
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with these initial defaults and then go on to run the DELTA_CALIBRATE
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command as described below. If no defaults are available then search
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online for a delta calibration guide that can provide a basic starting
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point.
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During the delta calibration process it may be necessary for the
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printer to probe below what would otherwise be considered the plane of
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the bed. It is typical to permit this during calibration by updating
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the config so that the printer's `minimum_z_position=-5`. (Once
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calibration completes, one can remove this setting from the config.)
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There are two ways to perform the probing - manual probing
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(`DELTA_CALIBRATE METHOD=manual`) and automatic probing
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(`DELTA_CALIBRATE`). The manual probing method will move the head near
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the bed and then wait for the user to follow the steps described at
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["the paper test"](Bed_Level.md#the-paper-test) to determine the
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actual distance between the nozzle and bed at the given location.
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To perform the basic probe, make sure the config has a
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[delta_calibrate] section defined and then run the tool:
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```
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G28
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DELTA_CALIBRATE METHOD=manual
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```
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After probing the seven points new delta parameters will be
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calculated. Save and apply these parameters by running:
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```
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SAVE_CONFIG
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```
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The basic calibration should provide delta parameters that are
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accurate enough for basic printing. If this is a new printer, this is
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a good time to print some basic objects and verify general
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functionality.
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Enhanced delta calibration
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==========================
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The basic delta calibration generally does a good job of calculating
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delta parameters such that the nozzle is the correct distance from the
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bed. However, it does not attempt to calibrate X and Y dimensional
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accuracy. It's a good idea to perform an enhanced delta calibration to
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verify dimensional accuracy.
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This calibration procedure requires printing a test object and
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measuring parts of that test object with digital calipers.
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Prior to running an enhanced delta calibration one must run the basic
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delta calibration (via the DELTA_CALIBRATE command) and save the
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results (via the SAVE_CONFIG command).
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Use a slicer to generate G-Code from the
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[docs/prints/calibrate_size.stl](prints/calibrate_size.stl) file.
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Slice the object using a slow speed (eg, 40mm/s). If possible, use a
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stiff plastic (such as PLA) for the object. The object has a diameter
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of 140mm. If this is too large for the printer then one can scale it
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down (but be sure to uniformly scale both the X and Y axes). If the
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printer supports significantly larger prints then this object can also
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be increased in size. A larger size can improve the measurement
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accuracy, but good print adhesion is more important than a larger
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print size.
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Print the test object and wait for it to fully cool. The commands
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described below must be run with the same printer settings used to
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print the calibration object (don't run DELTA_CALIBRATE between
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printing and measuring, or do something that would otherwise change
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the printer configuration).
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If possible, perform the measurements described below while the object
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is still attached to the print bed, but don't worry if the part
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detaches from the bed - just try to avoid bending the object when
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performing the measurements.
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Start by measuring the distance between the center pillar and the
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pillar next to the "A" label (which should also be pointing towards
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the "A" tower).
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Then go counterclockwise and measure the distances between the center
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pillar and the other pillars (distance from center to pillar across
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from C label, distance from center to pillar with B label, etc.).
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Enter these parameters into Klipper with a comma separated list of
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floating point numbers:
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```
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DELTA_ANALYZE CENTER_DISTS=<a_dist>,<far_c_dist>,<b_dist>,<far_a_dist>,<c_dist>,<far_b_dist>
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```
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Provide the values without spaces between them.
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Then measure the distance between the A pillar and the pillar across
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from the C label.
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Then go counterclockwise and measure the distance between the pillar
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across from C to the B pillar, the distance between the B pillar and
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the pillar across from A, and so on.
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Enter these parameters into Klipper:
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```
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DELTA_ANALYZE OUTER_DISTS=<a_to_far_c>,<far_c_to_b>,<b_to_far_a>,<far_a_to_c>,<c_to_far_b>,<far_b_to_a>
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```
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At this point it is okay to remove the object from the bed. The final
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measurements are of the pillars themselves. Measure the size of the
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center pillar along the A spoke, then the B spoke, and then the C
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spoke.
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Enter them into Klipper:
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```
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DELTA_ANALYZE CENTER_PILLAR_WIDTHS=<a>,<b>,<c>
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```
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The final measurements are of the outer pillars. Start by measuring
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the distance of the A pillar along the line from A to the pillar
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across from C.
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Then go counterclockwise and measure the remaining outer pillars
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(pillar across from C along the line to B, B pillar along the line to
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pillar across from A, etc.).
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And enter them into Klipper:
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```
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DELTA_ANALYZE OUTER_PILLAR_WIDTHS=<a>,<far_c>,<b>,<far_a>,<c>,<far_b>
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```
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If the object was scaled to a smaller or larger size then provide the
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scale factor that was used when slicing the object:
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```
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DELTA_ANALYZE SCALE=1.0
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```
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(A scale value of 2.0 would mean the object is twice its original
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size, 0.5 would be half its original size.)
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Finally, perform the enhanced delta calibration by running:
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```
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DELTA_ANALYZE CALIBRATE=extended
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```
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This command can take several minutes to complete. After completion it
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will calculate updated delta parameters (delta radius, tower angles,
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endstop positions, and arm lengths). Use the SAVE_CONFIG command to
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save and apply the settings:
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```
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SAVE_CONFIG
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```
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The SAVE_CONFIG command will save both the updated delta parameters
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and information from the distance measurements. Future DELTA_CALIBRATE
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commands will also utilize this distance information. Do not attempt
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to reenter the raw distance measurements after running SAVE_CONFIG, as
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this command changes the printer configuration and the raw
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measurements no longer apply.
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Additional notes
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----------------
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* If the delta printer has good dimensional accuracy then the distance
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between any two pillars should be around 74mm and the width of every
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pillar should be around 9mm. (Specifically, the goal is for the
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distance between any two pillars minus the width of one of the
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pillars to be exactly 65mm.) Should there be a dimensional
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inaccuracy in the part then the DELTA_ANALYZE routine will calculate
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new delta parameters using both the distance measurements and the
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previous height measurements from the last DELTA_CALIBRATE command.
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* DELTA_ANALYZE may produce delta parameters that are surprising. For
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example, it may suggest arm lengths that do not match the printer's
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actual arm lengths. Despite this, testing has shown that
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DELTA_ANALYZE often produces superior results. It is believed that
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the calculated delta parameters are able to account for slight
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errors elsewhere in the hardware. For example, small differences in
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arm length may result in a tilt to the effector and some of that
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tilt may be accounted for by adjusting the arm length parameters.
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