Sensorless homing without z probe
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Hi guys! I'm rebuilding an old hypercube, after some tweaking in the printed parts now I'm stuck with the firmware configuration. My starting idea was to keep the build as simple as possible, so I want to make the printer sensorless homing on every axis, also z. Is it possible? I'm a complete noob with firmware compiling, where can I start? Thanks
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@Massimiliano1991 You don't need to compile the firmware, just set up the configuration. For sensorless homing, see https://docs.duet3d.com/en/User_manual/Connecting_hardware/Sensors_stall_detection
For Z note that it can be difficult to get stall detection working on Z if you have a high step per millimetre, and you're using leadscrews, because the motors have a great mechanical advantage over the Z carriage. You will need a hard stop to stop it against, and usually that's with the bed at the bottom (ie max) end of the axis, rather than against the nozzle. Do you not have a Z probe you can also use for Z homing?Ian
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@droftarts hi, when i initially brought the 3d printer (probably a year ago) it was set up with a inductive probe but as i said before i wanted not to use it mainly for two reasons: one is because i want the printer with less wiring possible and a neat hotend carriage; and the other one is because i never found clear instruction on the offset from the tip of the hotend to the probe. What i was thinking to do is set a manual hard stop at a determined height, without using the nozzle as a stop. Is it possible? and then adjust always manually the correct offset from the bed. thanks for pointing me in the right direction for what concerne sensorless homing, is it possible to have it running without stallguard? thanks for your reply
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@Massimiliano1991 Which board do you have? If it's a Duet 3, you could fit a 1LC toolboard. This reduces wiring to power (2 wires) and CAN-FD (two wires), but then you can mount anything you want on the carriage.
Sensorless homing relies on Stallguard to operate, but you only need to have that enabled during homing, it can be disabled the rest of the time.
What i was thinking to do is set a manual hard stop at a determined height, without using the nozzle as a stop.
Yes, you can do this, but it needs to be at the other end of the axis from the nozzle. Otherwise, how can you go past it to then get the nozzle to the bed?
Also, stall detection is not usually as accurate as other endstop methods. As it says here https://docs.duet3d.com/en/User_manual/Connecting_hardware/Sensors_stall_detection#limitations-of-stall-detection:
The stepper drivers only update the stall detection state every 1 or 4 full steps, depending on configuration. So the actual position of the stall is uncertain to either +/- half a full step or +/- 2 full steps. This means that when using stall detection to replace endstop switches, the position defined by the stall is much less accurate than with typical endstop switches.
This can make quite a difference to your first layer height. It's less important for X and Y, unless you're restarting a job after a power failure. Generally, I'd recommend using a Z probe.
How to set the nozzle offset: https://docs.duet3d.com/en/User_manual/Connecting_hardware/Z_probe_testing#measuring-probe-x-y-offset
Though the whole of this page is worth a read to get good Z probe consistency.Ian
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@Herve_Smith hi, that's why i'm here and yes, i always refer to firmware if i have to do any tweak (now i know what fw compiling means).
@droftarts i think that's a bit too much for my knowledge, at the moment i'm ready the documentation and working on the support for the z probe. what i've not found is the height offset between the nozzle and the probe, does it exist or is like a bit of trial and error? thanks -
@Massimiliano1991 said in Sensorless homing without z probe:
what i've not found is the height offset between the nozzle and the probe, does it exist or is like a bit of trial and error?
It's the previous section in the link I already posted: https://docs.duet3d.com/en/User_manual/Connecting_hardware/Z_probe_testing#calibrate-the-z-probe-trigger-height
Ian
