Quad Z Sensorless Homing + BLTouch
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@graybilldustin I don't see a S parameter on your M915 command to set the stall sensitivity.
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@graybilldustin You also don't seem to be actually setting stall detection on Z only on X and Y? Also you seem to be setting the Z position to zero with G92 Z0 but surely that will be at your max Z height if the motors have just stalled? Also If you are going to use a mesh, I'd strongly suggest that you use the probe to set your Z=0 position and ideally use one of the same points that you probe during creation of the mesh.
Finally are you using belts or threaded rods for your Z axis? Using stall detection on threaded rods can be very tricky to get working.
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I changed it to M915 X Y Z S-64 R0 F0 and it still does not seem to work.
The G92 Z0 is left over from the default file I just haven't changed it yet, I was more concerned with getting the stall detection to work first.
I am using rods, this is the first I have heard anyone mention it being harder to do than with belts. My prusa minis use sensorless homing on the Z axis with rods. What in particular makes it harder to do?
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@graybilldustin said in Quad Z Sensorless Homing + BLTouch:
I am using rods, this is the first I have heard anyone mention it being harder to do than with belts. My prusa minis use sensorless homing on the Z axis with rods. What in particular makes it harder to do?
See for instance:
https://forum.duet3d.com/post/300230
https://forum.duet3d.com/topic/17314/sensorless-homing-stall-detection-lead-screw
https://www.klipper3d.org/TMC_Drivers.html#limitationsI'm sure if you spend a little time searching you will find other similar comments.
I'm still not sure why you want to home the bed this way, if you have a probe why not use that?
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@gloomyandy said in Quad Z Sensorless Homing + BLTouch:
sure if you spend a little time searching you will find other similar comments.
I'm still not sure why you want to home the bed this way, if you have a probe why not use thatWhen I shut the machine off and some of the motors fall down and the entire gantry is slightly crooked, then what do I do?
In all of those other posts people mention mechanical advantage which doesn't really make sense. A stall is a stall. When it hits the mechanical end stop the motor can not turn any further regardless if it is driven by a belt or a screw. I could see mid print stall detection on a screw not working well but sensorless homing should not matter in this way. I am convinced that I have some settings wrong. I have previously only used Marlin and Rep Rap is a whole different beast that i'm still struggling to understand.
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That's not the same thing. When the gantry is crooked the nozzle is crooked to the bed and you will end up with artifacts on flat top layer surfaces because the nozzle is not flat.
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@graybilldustin That is exactly what the auto levelling is designed to handle, what makes you think it is not suitable?
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Common problem on a lot of forums but I hoped this one was going to be different. I came here to ask for help to do something, not to ask for recommendations on what to do. Everyone has different ways of doing things and reasons for that. I have decided what I want to do and just needed help figuring out how to do it. I was not asking for something crazy that isn't supported so there wasn't any reason to tell me to do something else. And lastly my BL Touch doesn't get close enough to my screws for this to work. In one corner the probe is probably at least 4" away from the screw
I was able to figure it out on my own and it works absolutely perfectly. For those that think a lead screw doesn't work with sensorless homing that is 100% inaccurate as long as you have a hard stop that will completely stall the motor and not just flex when the end is reached. As long as your axis hits a hard stop and the motor completely stalls sensorless homing works just fine.
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@graybilldustin I'm glad you have it working, but I'd still recommend that you use the probe to set the Z=0 point if you plan to use a bed mesh. Doing it that way will avoid a lot of potential problems with the mesh having an offset from the bed especially if you make sure the probe point you choose aligns with one of the points in the bed mesh.
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