Thank you for help!..
new parts arrived…installed new spools and ran couple different calibration setups… couple nay, and some yay’s 
- my frame is horizontal, roughly 4170x3130 mm,
- with mounts in concrete, 3 cm deep,
- spoil board 22 mm from few smaller OSB sheets.
- the very first attempt with firmware 1.21 was successful for work area 2500x1200 mm but I didn’t save the yaml, just the log
- All other attempts had low fitness.
- I’ve noticed the lowest (bottom left) belt can touch the vacuum adapter when sledge drifts around so I’ve fixed it with a bit of heat. not pretty but has a bit more space.
- I ran into a few issues with the 1.21 firmware
- (after some failed calibration, or network reconnect it stops responding - it logs the action but won’t do it (lowering z-axis, release tension…).
- Restarting triggers unknown state → all has to be disassembled, retracted etc… that’s a bit annoying to do repeatedly :]
- Downgraded to 1.19, replaced the yaml file with one from git, reduced work area from 2500x1200 to 1500x900 and got 0.59. yay, ok, I’ll lower my expectations for now
A few questions
- What are okay fitness values? 0,45 is the minimum, but what is good enough?
- I’ve read that calibration force doesn’t need to be super high. I’ve used 800… does increasing it in horizontal layout helps with anything?
- Is my frame size large enough for 2500x1200 mm sheet?
- The top left arm has quite steep angle with anchor — during the later calibration phase (around waypoint 70), when it moves from the last bottom left to top left edge, the sledge lifts.
- Would raising the mounting point for top left anchor help? I can try to use a longer bolt with spacer under the belt end, but not sure if calibration counts with these adjustments.
- When replacing spools, there seems to be a bit bigger wiggle room than I thought, can’t this affect accuracy? especially with the top arm?
- Calibration should start from the center, but when it fails, the sledge is on the right edge. Next recalibration usually has much lower fitness values than when I start from the center. Does it have a negative effect? or doesn’t matter where it is now?