flarenut (flarenut) wrote,

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When faced with an intractable software problem, check your hardware

My cupcake CNC is getting to be like George Washington's hatchet. I replaced the old DC extruder motor with a stepper motor, then replaced the whole extruder with home built. Assembled the automated build platform, replaced the plastic assembly surface with steel, then cannibalised its parts for a plain heated platform with a copper surface. Installed a couple fans to cool the stepper and the driver boards. Threw in some LED lighting.

I still want to install end stops, maybe a geared extruder, maybe countersink the bolts on the build platform. Oh, and I've been upgrading the firmware. It runs much better under sailfish, what with smooth acceleration and not shaking the whole thing to bits. Or at least it did until I went from Build 973 to Build 1029 -- which also comes with a huge warning screen about not printing with a USB connection, unfortunately the only way I print.

Everything sucked. The extruder went completely wonky, the filament wouldn't stick to the build surface, prints that had been coming out fine were suddenly complete failures. So I downgraded the firmware, build by build back to what I had been using. Nothing. I downgraded the host software, replicator-g. Still crap. And all through this I knew the extruder was working, because I could spit out filament manually and it was fine. We're talking days here. Or nights rather, because I've got stuff to do during the day.


Then it struck me: what was that random jumper wire hanging out of a connector? It wasn't the led lighting, because that was OK. It wasn't the fan for the extruder stepper, because that went around back. Or the fan for cooling PLA because I took that off. It was the fan that cools the stepper driver for the extruder, which is cranked all the way up because it really doesn't have enough oomph to push the filament at full speed.

I touched the heat sink on top of the driver chip and burned the hell out of my finger. Aha. The driver chip has a thermal cutout to keep it from blowing up under excess load, and it was working just right . So when it got into a print, the chip would overheat and stop working, cool down a few hundred milliseconds later and start up again, overheat and stop, cool down and so forth. Resulting in some fraction of the intended filament coming out at unpredictable times. Or not.

I plugged the jumper back in, the fan stated whirring, then the jumper fell back out. So tonight I made a heavier gauge jumper. Printed something and it mostly worked. Hurrah.

But. The result of all this upgrading and downgrading and testing is that I really don't trust all the software any more. So I may upgrade very very slowly, or just leave things as they are, and walk very quietly when I'm anywhere near the cupcake. Whee.

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