As soon as I replaced them with the first available GT2 6mm Fiber Glass Reinforced from Aliexpress, all problems with automatic calibration were gone.It really became automatic.Before that, you still had to manually adjust the machine.Each shoulder needs 148.5mm if I measured correctly.The Flsun QQ-S is equipped with an MKS Robin Mini board from Makerbase.Its main advantage is STM32F103ZE with a built-in coprocessor that performs any operations with floats in just one cycle!!!This is a huge advantage for any delta printer with its simple kinematics but complex system of coordinate equations.The disadvantage of the board is the non-replaceable A4988 drivers with their "salmon skin" effect.I had to remove the 10KΩ resistors from the 13 legs of the drivers - skipping steps and moiré were gone.The article why not tl-smoother and why is here.The board diagram is here.We change all Rm6_Mx to jumpers.I'm waiting for the GT2 6mm Idler Timing Pulley 16 Tooth 3mm Bore because it's not good to crawl teeth on a flat pulley, and their diameters are dancing + -0.3mm.Those there are not cylinders, but cones.