Sensorless homing B axis problem

[dagrende]

State of my build

• mechanics ready - mostly the same as jyjbird
• Fly E3 Ultra with ESP32Eth WiFi add-on
• All motors, sensors, fans and hot-end heater connected and tested
• reprap firmware 3.5.4 and wifi installed and running
• control through Duet Web Control works
• config files based on jyjbird reprap firmware config from Apr 2
• enabled to4axis as required by S4_Slicer

Now I have problems getting homing to work in 4axis mode. X homing works perfectly. B homing (extruder angle) not. It runs into the stop tab and the two motors jumps over a number belt teeth before stopping (a heart breaking sound). It seems to consider B homed, though, as the UI says: The following axes are not homed: Y, Z, C
My config files can be viewed on my github fork: https://github.com/dagrende/Core-R-Theta-4-Axis-Printer/tree/main/reprap%20firmware%20config.

It would be extremely useful if anyone with a working x and b homing could publish all ten (or so) config files, as a reference, for me and others to use when getting things working.

When I get it working I will publish a number of notes and mechanical mods I have have made to the original jyjbird parts.

[the-Geeson]

Just to check, did you put the jumper on the boad to enable sensorless homing? I have the same board but it didnt come with jumpers so had to order some

[dagrende]

This is my driver and jumper config:

Driver no	PCB marking	Jumper	My use
0	E1		Z axis stepper
1	X	no	C rotation stepper
2	Y	yes	X (lower) stepper
3	Z	yes	B (upper) stepper
4	E0		Extruder stepper

[Bolado]

One thing to consider and check as well (if you followed @the-Geeson's advice) is the current and sensitivity settings for the sensorless homing on the two steppers that control the B-axis (two? I think it moves only one to home B right? You get it hehe).

These values can change for everybody because the stepper model, belt tension, and other factors can vary from printer to printer. It's crucial that you find the right sensitivity yourself by following a guide like this one from Duet3D.

I mention this because on my experience on Klipper side of things, I know a 10% difference in the current can mess up the sensitivity, and a 10% change in the sensitivity value can mess up homing. Looking at your configs, the homing currents are different for the X and B axes. I believe they should be the same since they use the same stepper motors, right?

The fact that the motor keeps forcing and skipping is likely because it only stops when it completes what it thinks is a 400-degree rotation, instead of when it actually stalls, so if it's firmware side of things, or you have to tweak the currents to find the sweet spot, or follow a guide to tune the sensitivity value.

Keep us posted and good luck!

[dagrende]

Thank you for a lot of advice! I'm a Klipper guy too. It was much easier to configure sensorless homing on my Voron 2.4.
I think I know what's wrong with B homing here. I assumed the direction of B rotation when homing should be clockwise, as it is on the jyjbird video on the Core-R-Theta printer. But the STL file extruder axle mount plate is made for counter-clockwise homing. I'm printing a mirrored mount plate now. I'll report the result!

[dagrende]

The same problem with counter-clockwise B homing. I have set down X, B current to 10% of normal current, and have sensitvity set to the lowest recommended level with M915 X B R0 F0 S-10 but the motors still struggles and misses steps when hitting the rotation stop tab. It is strange that the M913 X50 B50 g-code doesn't seem to have any effect.
And X homing is so smooth - it just touches the stop twice, instantly detecting it both times.

Do you, @Bolado have sensorless homing working?

[Bolado]

Do you, @Bolado have sensorless homing working?

My build right now is on halt for now due to exams and now vacation :/

Have you checked this?

The diagpins looks too different and you have to calibrate the sensitivity of course, so you would need to start with the maximum sensitivity till homes fully (from -127)

[EmmanuelMess]

We are having the same issue, could you figure it out?

[damian238]

If push comes to shove, you may have to implement something lifted from security alarm projects.If you impose a two stage process wherein an initial trigger raises a flag, slows the motor to a crawl such that there is minimal inertia from the motor's mass to overshoot the end stop. The flag can be driven by a momentary switch in which one line in series could serve all axes. 
If you don't have even one extra switch port on your board, then the only thing I can suggest is to force the entire homing process to proceed at a crawl.

[EmmanuelMess]

We have tried reducing the speed, but there is a software check to ensure that the stall is detectable, and that check fails, and the homing cannot start.

[oldnslow]

Have you had a look at Teaching Tech's video on setting up a Fly board for sensorless homing?, although it is a little dated perhaps it covers something you have not looked at yet.

[EmmanuelMess]

@oldnslow Thanks for the video, we'll take a look.

The initial homing files we used for the printer were the ones you provided in your repo (I think they were copies from the ones in this repo, but might have had some changes). Did you have any issues when homing the B axis?

[EmmanuelMess]

Okay, it seems that it was homing in the other direction, but gave a false positive, when it went back it hit the actual backstop and kept going, twice. Its fixed now. Thanks for the help.

[oldnslow]

Good to hear you are making progress!

You are correct that the homing files in my repo are currently unchanged copies of the jyjbird originals. I must confess that my printer is not built yet (hopefully in a couple of months) so i have yet to work through and document the sensorless homing process.

If you are able to share your homing config file when you are happy with it (and any comments if you have time) i will update my repo/wiki in order to hopefully help others dealing with this issue (and myself of course!).