They measure a series of points to get a bed mesh, the same as other leveling sensors do. You shouldn't need to live-adjust z, because you've measured the bed surface with the nozzle tip.
With a BLTouch, you need to adjust the z-offset, because the nozzle tip and the BLTouch trigger height are not the same. Once that is calibrated, it should continue to work fine as long as the sensor is working properly.
I think it mainly comes down to the accuracy of the sensor. If your sensor gives you a +-0.03mm reading when probing the same spot, then you will have high and low spots in your bed mesh that you can't correct with z-offset.
This could explain your issues with the BLTouch you mentioned in another thread here. I have various brands of knockoff BLTouch sensors, and the worst one had a +-0.02mm range when measuring points, which made it impossible to get a good bed mesh. The one I replaced it with had about a +-0.005mm accuracy, which fixed my issues with the low and high spots.
I've measured the repeatability on mine, and it was pretty good, though I don't remember the number right now.
The pressure sensor on the hottend is superior to any other method, because it has much better resolution (though maybe not better than the Beacon), and it can adjust to print conditions in real time, which no other start-of-print sensor can do.
You mean in response to pressure changes during print? I’m not sure but that would be nice!
I do have two BLTouch printers and lots of Prusas with the PINDA inductive sensor. What excites me about direct nozzle force sensing is that it eliminates the need to calibrate z height offset between the sensor and the nozzle. I don’t know if Bambu’s bed sensor is as good as Prusa’s nozzle sensor but anything that eliminates the mechanical stack up between nozzle and sensor is an improvement IMO.
Though I do realize much of my gripes come from the fact that the PINDA mount on the Prusa Mk3s is kinda weak and I’ve had several fail, requiring an annoying service job.
Yes, exactly! I'm very excited by it, if it works well, it'll be a revolution. Any other sensor that measures the bed is strictly worse, because it only does so once, rather than continuously. The Beacon does look pretty great, though.
Yes, I have one and it works exceptionally well. The only caveat is that it’s measuring the metal surface directly and not the actual physical surface (such as PEI), so you need to load different offsets if you swap between different material surfaces such as textured PEI, flat PEI or bare steel.
Oh, how does it do it? I thought it used light/laser to measure, if it's measuring the metal it might not be very accurate with my two layers of magnet and PEI sheet on top...
It generates a field using the coil measures the eddy currents in the material directly below it. As long as you have a spring steel sheet and don’t have those large discrete magnets (either lots of tiny round magnets or the sheet magnets) it works just fine.
It’s accurate to single digit micrometers (yes, actually).
Wow, that's impressive. Aren't most buildplates made of aluminium, though? Also I always worry that the PEI sheet over the plate will introduce inconsistencies, let alone that mine has an extra layer of magnet sheet on it (and, as you said, the magnet even makes the detection not work).
However, it seems very doable to have a Beacon for the bed scanning, and a BLTouch for getting the physical distance over the sheet plate.
Most PEI sheets are quite uniform so you don’t really have issues with that. As long as they’re applied to the build plate without bubbles they’re generally as flat as the plate surface.
Also, no, almost no build plates are aluminum. Modern printers usually use a silicone heater bonded to an aluminum frame, which either has magnets embedded in it or a sheet magnet applied on top of it, then a spring steel plate with some sort of PEI on top is what you print on. That’s what Prusa and Bambu use, for instance.
I don’t know why you’d want to use BLtouch to get the physical distance, since you calibrate the physical distance when calibrating the beacon sensor itself. Not a problem unless you frequently swap between materials of different thicknesses.
> Not a problem unless you frequently swap between materials of different thicknesses.
Yep, exactly, I have a PEI sheet (with a magnet) and it has a smooth and a rough surface, and I end up swapping between them sometimes. I guess it doesn't really make any difference, since they're both the same height (as they're two sides of the same sheet), but, as you say, my magnet sheet ruins the Beacon homing anyway.