Hi all, just finished the entirely satisfying first segment of the V3 LR dual build (purchased now early July 2024) and drawn some pretty neat crisp (relatively accurate) crowns which is a great start, all things prior to this went smoothly.
…then…
On re-homing after one of the crowns I had both the far Z and Y endstops overshot with the belts and leadscrews jumping. After unplugging & powering up again I rehomed a number of times without issue and redraw a crown. After fiddling and checking Z offsets, squareness etc again it did it again. I popped Ryan a mail and he advised to get a thread going so here I am!
When it did this I got a video of all the end stop LED’s doing what they should (being lit) as well as the limit switch being swquidged. I have also had a case where the machine was overrunning and then it stopped after about 5-10 stepper ‘clicks’ on the far Z.
All switches are the correct NC wiring, the machine is well adjusted, and the steppers & end stops are not swapped.
I did a fairly moderate dive into this and it seems SKR has had issues with stuffing up the logic level voltages which meant the mobo didnt register a high logic level (when the end stop was triggered because the LED sucked up some current). From what i’ve read it seems either pull off the LED’s (which i dont think is an elegant solution) or wire up a little pigtail with some pull up resistors.
I am very close to trying the pull ups to see if that solves the issue but Ryan indicated that may not be the only possible culprit and pointed to poor connections on the highly annoying and fiddly little wire crimps. I measured the voltage and it just scraped 2v which according to google is on the limit for triggering a 3.3v logic high which makes sense why this is intermittent. I wrongly assumed initially that if the LED’s are lit then the firmware ‘knows’ but this isnt the case due to how its wired.
I cant access M119 WHILE its clicking, just get “busy processing” which I assume is because it hasnt finished its homing process.
Wondering what y’all thoughts are on this and if anyone has put a scope on the connections to see whats going on? Perhaps I should measure the resistance of the microswitch loop but havent seen what a good or bad resistance is.
Thinking about this a bit more, when the end stops are hit, circuit goes open and thus the effect of poor wire crimps is irrelevant as there is no current flow in the circuit. What is relevant is that the signal pin voltage is not pulled high enough to trigger the high logic level and that can only be achieved by external pull up resistors or LED removal. I’ll put a scope on this and post results.
Ok so the first image is the Saleae connected to gnd and signal pins, and as expected, when the switch is pressed and released we go between 0v and a smidge over 2v.
The second image is with the Saleae connected to the same gnd and signal pins during a z-homing with the first bounce being the first trigger and then the delay to the second trigger as the gantry rises up. I wanted to see if the stepper running had any effect on voltage spikes but granted this was a slow 6khz sampling rate.
To me, this points towards the external pull-up resistors being required and the problems on the SKR boards not being sufficiently rectified or just resurfacing?
This seems VERY likely to be the end stop resistor issue. I recently had almost identical issues, where it would initially home correctly, then fail to home a second time a few minutes later (driving past the end stops). LEDs worked every time, but the motor wouldn’t stop.
There were a few batches of BTT boards that had a bad implementation of LED monitor circuit which needed a workaround to work reliably. This could be via soldering resistors on the boards, or as noted below with making a pigtail to install inline with the endstop wiring.
Did this work for you, ? I’m having the same issue, and have been looking into linuxcnc, which I will be doing in the long run, but for now this may help me also. I figured it had to do with the board and I’ve been fighting this for months. At first I figured it was me not knowing what I was doing, but slowley started leaning towards this being a bad board. I didn’t get my board from Ryan, he was out of stock.
Every time this thing goes nuts I have to reset and realign the machine.
The best way to troubleshoot would be for you to open up a new troubleshooting topic.
The community can help you from there, no matter where you sourced your parts.
Include details about your machine, which controller (specifically) you have, what drivers, what firmware, and good high resolution pictures of your board.
If I recall correctly you have a LR3, SKR Pro 1.2, and I gave you bum advice due to mixing up marlin mode and TFT mode wiring colors. I think your board didn’t have heat sinks on the TMCs, so that might be something we check as well.
I think you had some firmware or bootloader troubles, so we might want to revisit that as well.
Looking forward to your new topic so we can jump in and help.
Since I added the resistors mentioned above I’ve not had a single poor end stop honing event. Granted I haven’t done hundreds of homing but it hasn’t happened again so I’m 99% sure this solved my problems.
I’d suggest carefully measuring the voltages on the logic/sense pins during trigger state as this would also give an indication as to whether this corrective action is right for your hardware. Mine measured only 2v when pulled high (end stop triggered and circuit open). With the additional 1k resistor I’m up to 2.65v.
I read a few more posts with the same problem and Ryan suggested to someone else to just break of the end stop led’s. So that’s what I did, it’s been a wonderful day, so far all those problems have gone away , every time I hit home it works the way it should. Both Y motors moving, before only one would move, sometimes, and the Z would just keep driving. both situations . I’m sure were throwing off the squareness. Basicaly I could never run the machine for 4 or 5 hours like I did today.
Yeah, I read about the LED’s too but I wanted to maintain the LED’s for problem solving down the road if needs be. I also read about pulling the LED’s off which can damage the PCB traces and lead to other problems hence I went the external resistor route.
Glad you got it solved, its great when it all works
