I believe the bed steppers have load sensors, as it will stop if you touch it while its raising but does anyone know if there’s a load sensor on the extruder stepper? Twice now i’ve found the machine printing in mid air because the filament has had a tangle (likely my fault) and the reel has been caught up on the holder, or dryer box, lifting it off the table. Each time I’ve been able to unload/load the filament without any other issue but I thought it would have had some sort of protection built in and stopped before getting to this stage. This is for P1P
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I have had the same problem when the filament was attached to the spool at the end. The filament is still keeping the filament run-out sensor active so the extruder keeps turning. It does not care if the filament is moving or not.
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Exact this happend to me too some weeks ago. 
There is load sensing on the XY axis motors that is used when homing, but the Z axis uses a piezoelectric sensor on the bed which is why it stops if you touch it. And that’s also why it happily skips trying to go down when already on the bottom 
The filament sensor is a simple hall switch, there’s nothing to indicate that filament isn’t moving, just that it isn’t there. I don’t think that’s a huge problem as I only had a couple clogs, usually caused by me switching from high-temp Nylon to PLA rightaway without cooling anything, or when the spool had a tangle. If you get too many failures like that then you’re doing something wrong.
I’ve had an other type of loading issue that will make you laugh…
I switch from non-AMS material such as PAHT-CF in it’s own dryer and PTFE tube connected to the X1-C (AMS PTFE tube disconnected, of course) and then go to another print using filament in the AMS but forget to reconnect the AMS PTFE tube…and guess what happens???
The AMS loads the filament but, since it’s tube is not connected to the Bambu, the entire spool gets fed and winds up coiled on the floor. LOL!!!
from what I see on X1C no steppers have “load sensors”.
bed is held on the piezo sensors so if you press the bed it will trigger the sensors and this is used for probing. XY motors do not have any sensing but the stepper driver measures the current and can detect motor stalling and this can be used for homing without separate homing sensors (you lower the motor current, drive the head to the wall, when stepper driver detect stall you assume you know where the head is)
there is only filament presence / filament runout sensor there
The filament is present at the extruder so the sensor is not triggering. “load” sensing here do not make much sense as it could hardly be used to detect situation like that. Only proper sensing is filament movement sensor (like the laser one on some prusa’s or like the Duet3D filament monitor or any other filament monitor that actually measure how much filament passed through extruder (usually rotating magnet or encoder or a laser sensor like one in an optical mouse) so the printer can detect that less filament moved than expected detecting a clog/blockage/any other issue
maybe, maybe not, I’m printing since the age of Darwin, so around 15 years and I never had these issues with 10s of printers I made and 20+ printers I purchased, modified… and with X1C printing from the filament holder on the back of the printer I had issues where printer retract filament enough to take it off the spool and on to the spool holder then tightly wounding that filament around spool holder making filament unpullable … this happened 3 times in a row so I disconnected the back spool holder and thrown it into garbage as that concept obviously do not work with X1C, I printed the Y splitter with one M10-4 and one M10-6 connectors on the input so to M10-4 I feed tube from the AMS and to M10-6 I feed the 6mm ptfe tube from drybox (I have bunch of eSUN’s eBOX dryers so I use them, they do not like wide spools but are great for everything else) and this way I have no issues any more when printing without AMS as when the printer feeds filament back it will coil back on the spool it will not fall to the side and tangle like with that holder on the back … I do not have X1C long enough to had time to check what exactly it is doing and why so many retractions, especially long ones, that would so consistently remove filament from the spool and on to the spool holder but problem is easy solvable by using a drybox + ptfe tube between drybox and printer
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Yes, I should have said current sensing drivers ie load. I’m surprised they haven’t figured out how to implement this with the extruder stepper but maybe it produces to many false positives. I have seen people make wheel type and micro switches to detect when the filament is being pulled too hard but I wouldn’t know where to tap into the board to get the signal to trigger a pause. It could just trigger a buzzer or something to warn but no good if you’re not home to hear it and action.
you cannot do it 
with extruder stepper
check out some videos on YT where ppl added a load cell to the extruder to measure forces there, extruder is pushing filament pretty hard… also, the issue is that most extruders will not stall, they will grind off the filament and continue to rotate while the filament is not moving so any measurement on the extruder motor is useless for detecting clogs, blocks, twisted/tied/messedup filaments etc… they ONLY way to detect that is filament motion sensor. Prusa had one (not very good as it is optical and will not work good with all types of filament) dunno if they still use it or they improved it I did not follow, Duet was selling one that had the same issue (not working with all types of filaments) but they upgraded to a better one, for both you can use “indirect” system that works super good as the filament moves a carbon fiber tube that sensor is sensing ( Improved Duet3d Indirect Laser Filament Sensor by kiowadriver - Thingiverse ), duet board support impulse input so you can use encoder (bigtreetech used to be selling one that works great with non-soft filaments but was almost impossible to use it with flexibles GitHub - bigtreetech/smart-filament-detection-module ) … afaik both marlin and klipper have support for encoder input for filament encoder sensor so should be easy to implement on any printer… now X1C/P1P are closed source so no clue if / how you can add sensor like this to them nor why bambu team did not decide to implement that sensor but it’s not a rocket science, I have filament flow sensor on almost all my printers (I made them myself, I’m using some cheap 600 steps/revolution encoders, enough precision for detecting issues)
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Yeah, mk3 sensor had the optical, they did away with it for the mk3s as it didn’t work reliably with all filaments eg clear.
yup, those optical ones have issues with some filaments but the indirect adapter for them solves that problem… it is the only good way to detect clogs and blockages and tangled filament