To achieve the Zipper Tree Challenge, I analysed extensively the list of sources of errors, found some missing parameters, then searched ways to set parameters right.
Below I summarize my findings about chain length calculation for accurate sled positioning
- the most critical machine parameters,
- the missing parameter in the current official firmware (items 4 and 7),
- the target accuracy needed for each parameter,
- and my advice about parameters quite impractical to measure directly and requiring a “calibration routine” help :
Now, either the firmware uses the actual sag correction value , or gets improved with accurate catenary correction using weights, but either way weights are missing and necessary in the firmware to identify chain stretch.
(edit) I invite you to look at the Wiki page showing the sled position accuracy vs precision where the sled position and chain properties are highlighted.