I have noticed lately that there are a lot of printers using strain gauges for bed leveling, typically with HX711 or HX717 conditioner/ADC ICs.
My question is, Why? It is not the use of strain gauges themselves that is my concern: Strain gauges can be stunningly sensitive, fast responding, and mechanically stable for long periods - and they can be cheap as well. My problem is that almost all of the implementations I have seen used very high contact force, often more than 500 grams: Videos on YouTube frequently show detectable vertical movement of the bed when the nozzle contact is made.
I accept that there are added attractions in using a strain gauge between the mechanical extruder and the hotend. This arrangement can measure the back force on the filament, both detecting blocked nozzle conditions and unusual conditions such as hard contact between the print head and the print. Having said that, the more typical design has the combined hotend and extruder hung on a single quarter bridge tongue, an arrangement that adds so much mass that it further limits the slow electronics of the HX711.
I admit also to some bias as I am happy with a single underbed piezo sensor for obtaining the Z reference position and a touch sensor for mesh probing the bed. But even this is not a firmly held belief and the crash of favorite technologies and ideas being kicked off their pedestals often makes my workshop a very noisy place.
I have asked this on this forum, where most of the few remaining denizens are polite. Asking the same on Reddit or the Klipper forum would have my throat ripped out (figuratively) and my body trampled into the dust (figuratively)
So the Why?? remains. Is it perhaps that the Duet Smart Effector and now the Prusa Mk4 have started an avalanche of copycats? Maybe people found the choice of BLTouch, inductive probe, capacitative probe, and nothing else a bit stifling.
Mike