Prusa/Mendel Gen 6 I1 - The hobgoblin...
Posted by cjrussell
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Prusa/Mendel Gen 6 I1 - The hobgoblin... August 24, 2014 06:02PM |
Hey guys, long time lurker, new poster.
So about 2 months ago, an associate of mine bought a brand new 3D Printer (new to him at least) and promptly trashed it in 2 days. From what I gathered, he crashed the extruder head directly into the bed and managed to engrave his last print straight into the aluminum before he aborted the print. He aborted a little late unfortunately. He decided this new 'tech' wasn't his thing and wanted to get rid of it. I told him I'd take it off his hands for spare parts if he wasn't interested. I then inherited a printer with no documentation, no instructions, no nothing. I decided I'd try fixing it before committing it to the great scrap pile in the sky.
From what I've gathered by my searches, its a Prusa Mendel printer with a Gen6 brain board. The type of extruder head, no clue. I don't even know what iteration it is, but by the looks of it, it's probably iteration 1. In the two months I've had it I have fixed several confounding problems with it. The first being the print head (thank god for 0.5mm drill bits laying about) and the print bed itself (extra Kapton never goes to waste...). The board itself needed to be reflashed and reprogrammed (not sure what happened there, put Marlin code into it), but it got named the Hobgoblin shortly thereafter. I tore out all the aluminum foil flags it was using for end stops (opto-stops) and printed out new ones from ABS. I should mention I have a Solidoodle Generation 1 (!!!!) at work I use for projects, yah...high tech stuff here. After moving the brain board to the side of the mounting, rerouting all the wiring, printing out a spool holder (didn't come with one, or even the location for one), and printing out stops for the leveling nuts on the bed, I finally have it in somewhat working order. There are, however, a few confounding problems remaining that I am facing at the moment.
The first being the proper stepper motor settings in the hardware. I tried all the settings I could find on the net, but none of them were correct. I eventually printed out a 10x10x10 cube and measured/adjusted the values until it came in close.
#define DEFAULT_AXIS_STEPS_PER_UNIT {39.506,39.506,3238.1,241.2} // steps per unit for Hobgoblin
If anyone knows what those values SHOULD be, I'd appreciate it, otherwise I'll leave them where they are.
Second problem, the "heated" bed. The designers choice for this was to strap 4, 1 ohm resistors in series to the bottom of the aluminum and dump 12V into them. While this indeed generate heat, it wasn't enough to keep the ABS/Kapton happy. At the moment, I've rewired it to be 2 resistors in series, with both chains in parallel. This has increased my current load from 3 Amps to 12 Amps (had to replace the wall wart of a power supply with a real ATX supply) and this appears to have helped that, but as it's still straight voltage, I can't control it. I've looked at the Seven Switch device to expand the main-board and allow for controlling it. Does this sound like the right approach?
Finally, I have the horrible cancer known as Z-Wobble. I greatly improved the wobble by not turning off the Z-Axis in the firmware, but I still have it to a degree. Now, I've seen plenty of couplers/attachments/prints that should help with this, but unfortunately, all of them are for a generation of printer greater than this one. In the infinite wisdom of the original design, this printer has only 1 (ONE) stepper motor for the Z-Axis, not 2. It's connected to a pair of threaded rods the X-Axis carriage rides on by a length of geared belt. The belt and gears are all stored below the printer itself. Now, the rods seem straight to me, but they are certainly not centered in their bearings. I can tell that just from watching them. Photos attached. I doubt I have the expert eye required to loosen these two rods up and recenter them by hand. I only wish. So, does anyone know of a possible solution to this issue? Perhaps some kind of coupling that would force the threaded rods into the center of the bearings?
Printer in full:
Right side Z-Axis/bearing assembly:
Left side Z-Axis/bearing assembly and stepper motor:
Top of the threaded rods (just hanging there!)
There's also a very strange cut-out in the print bed you might be able to see in the first photo. That's in the original photos from the manufacturer I'm told...so what's the point of it?
Any assistance would be a godsend guys. I'm trying to do what I can without rebuilding the entire bloody printer, just small modifications and fixes. This thing can't even bridge more than a 1/4", but that's gonna be a headache for another day...
So about 2 months ago, an associate of mine bought a brand new 3D Printer (new to him at least) and promptly trashed it in 2 days. From what I gathered, he crashed the extruder head directly into the bed and managed to engrave his last print straight into the aluminum before he aborted the print. He aborted a little late unfortunately. He decided this new 'tech' wasn't his thing and wanted to get rid of it. I told him I'd take it off his hands for spare parts if he wasn't interested. I then inherited a printer with no documentation, no instructions, no nothing. I decided I'd try fixing it before committing it to the great scrap pile in the sky.
From what I've gathered by my searches, its a Prusa Mendel printer with a Gen6 brain board. The type of extruder head, no clue. I don't even know what iteration it is, but by the looks of it, it's probably iteration 1. In the two months I've had it I have fixed several confounding problems with it. The first being the print head (thank god for 0.5mm drill bits laying about) and the print bed itself (extra Kapton never goes to waste...). The board itself needed to be reflashed and reprogrammed (not sure what happened there, put Marlin code into it), but it got named the Hobgoblin shortly thereafter. I tore out all the aluminum foil flags it was using for end stops (opto-stops) and printed out new ones from ABS. I should mention I have a Solidoodle Generation 1 (!!!!) at work I use for projects, yah...high tech stuff here. After moving the brain board to the side of the mounting, rerouting all the wiring, printing out a spool holder (didn't come with one, or even the location for one), and printing out stops for the leveling nuts on the bed, I finally have it in somewhat working order. There are, however, a few confounding problems remaining that I am facing at the moment.
The first being the proper stepper motor settings in the hardware. I tried all the settings I could find on the net, but none of them were correct. I eventually printed out a 10x10x10 cube and measured/adjusted the values until it came in close.
#define DEFAULT_AXIS_STEPS_PER_UNIT {39.506,39.506,3238.1,241.2} // steps per unit for Hobgoblin
If anyone knows what those values SHOULD be, I'd appreciate it, otherwise I'll leave them where they are.
Second problem, the "heated" bed. The designers choice for this was to strap 4, 1 ohm resistors in series to the bottom of the aluminum and dump 12V into them. While this indeed generate heat, it wasn't enough to keep the ABS/Kapton happy. At the moment, I've rewired it to be 2 resistors in series, with both chains in parallel. This has increased my current load from 3 Amps to 12 Amps (had to replace the wall wart of a power supply with a real ATX supply) and this appears to have helped that, but as it's still straight voltage, I can't control it. I've looked at the Seven Switch device to expand the main-board and allow for controlling it. Does this sound like the right approach?
Finally, I have the horrible cancer known as Z-Wobble. I greatly improved the wobble by not turning off the Z-Axis in the firmware, but I still have it to a degree. Now, I've seen plenty of couplers/attachments/prints that should help with this, but unfortunately, all of them are for a generation of printer greater than this one. In the infinite wisdom of the original design, this printer has only 1 (ONE) stepper motor for the Z-Axis, not 2. It's connected to a pair of threaded rods the X-Axis carriage rides on by a length of geared belt. The belt and gears are all stored below the printer itself. Now, the rods seem straight to me, but they are certainly not centered in their bearings. I can tell that just from watching them. Photos attached. I doubt I have the expert eye required to loosen these two rods up and recenter them by hand. I only wish. So, does anyone know of a possible solution to this issue? Perhaps some kind of coupling that would force the threaded rods into the center of the bearings?
Printer in full:
Right side Z-Axis/bearing assembly:
Left side Z-Axis/bearing assembly and stepper motor:
Top of the threaded rods (just hanging there!)
There's also a very strange cut-out in the print bed you might be able to see in the first photo. That's in the original photos from the manufacturer I'm told...so what's the point of it?
Any assistance would be a godsend guys. I'm trying to do what I can without rebuilding the entire bloody printer, just small modifications and fixes. This thing can't even bridge more than a 1/4", but that's gonna be a headache for another day...
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