M425 Backlash compensation happens too slow even with S1
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I have a machine with 1Z cantilever bed. I'm using a Stepper Online 10:1 precision planetary gearmotor for Z.
I'm measuring a backlash of 0.044mm. (which is about 80% of the datasheet max backlash). 22% of a standard 0.2mm layer height
With a M425 Z0.044 S1
There's too much lag in compensating the backlash to make bed mesh really useful.
Ideally i'd like it taken up as fast as the stepper motor driver can take the steps on the reversal. Can we have an option for that? Like -S0 says do the backlash comp as soon as is possible?
CroXY - Crossed Gantry Printer, Ultibots D300VS+, Custom CoreXYU
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@wesc backlash compensation isn't really intended for use in 3D printers, it meant for CNC machines. The problem is that when 3D printing we can't suddenly stop extrusion while the stepper motor takes up the backlash and then suddenly start it again. If we try to command the stepper motor to take up the backlash instantly, that it likely to result in missed steps unless the amount of backlash is small (well under one full step). The belt-driven axes used in most 3D printers don't usually have much backlash anyway.
Backlash compensation in CNC machines is easier. The speeds are generally lower and there is no extrusion to worry about; so backlash can be taken up without rushing.
How much is the backlash in your Z axis, converted to motor full steps?
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@wesc do you actually need the backlash compensation in Z?
Typically the weight of the bed will always keep the gearbox loaded on one flank even when you reverse directions. You'd only go across the backlash if you are using z accelerations approaching 10000 mm/s^2 (I.e. 1g) where you are outrunning gravity. Granted a bit of friction might make that number smaller in practice, but I doubt you'd be anywhere near those limits if your motor has to run through a 10:1 ratio.
It's different on X/Y axes where you don't have gravity always pulling in one direction. I know I've seen many printers with 'anti backlash' nuts on the z lead screws, but they just don't make sense to me from a physics point of view!
