Saturday, July 10, 2010

Success, Failure, Rinse, Repeat.

The controller bug has been conquered, by way of modified and recompiled firmware. A new extruder thermistor pin and a new thermistor table were all that I needed to get it up and running, and installing the mac ports of the various tools took less than an hour of concentrated effort.
Before I fixed the software I borrowed a techzone Mendel electronics set to use in case my hardware was irreparable, in return for a checking over of all the solder connections, a good testing, and some printed mendel parts. The stepper boards and motherboard initialized, and tested correctly, though I did not do any heavy lifting on them. The extruder controller is a totally different story. I wired myself a simple adaptor to turn the cat5 cable my motherboard uses into just the two serial comms wires used by the reprap wiring. This seems to have worked fine, I am incredulous that there could be something dangerous in two serial lines at 5v. When I plugged it all together and flipped the switch, above the fan spin up noises there were two distinct "pop" sounds and one particularly painful sounding hiss. I cut th
e power, and saw what I believe was the magic smoke escaping something on the extruder controll
er. I have not yet found out what parts burned, but I cannot find any visual leads with my naked eye. I re-checked all my wires, and tested the power rails, and found no issues. The controller board's power LED lights, but nothing else seems to work. I suspect it t
o be dead.

After bearing this news to the owner of the boards and promises to help repair the damage -- whatever it turns out to be -- I turned my attention back to extruding w
ith my own hardware.
The same guy who lent me his boards also gave me a nozzle that he
had cut with machines available at the University of Washington. I was not expecting a success from the first try, but the part, a combination nozzle and heatercore, managed to work on the first try with PLA. My mind was blown. We got to extrude at 255PWM, resulting in 33mm/s from the nozzle for at least 5 meters of testing extrusion. However, reality restored the normal order, and the nozzle jammed as soon as I stopped the extrusion to prepare for a print. I suspect this is because the thermal gradient is so tremendously long, as the entire hot part is 1cm long, followed by 2-3 cm of blank heater barrel The thermistor is a 3mm one, and placed just before the barrel enters the insulator. I will shorten it somehow and try again later this week. If this design works out my project will have spawned what I think may be another unique upgrade.
In trying to unseat the jam we seem to have burned out the Kysan 1156006 gearmotor. I am not sure what happened, but it no longer runs, even from my bench power supply. I'm working to replace it now.
In older news, I laser cut our machine a very nice filament spool and box, based 99.9% on the makerbot MK1 Filament Spool. Wheras the makerbot version runs $100, mine cost me $2 in metal nuts and bolts, as the handsome plywood was cut from free scraps, and the plastic was donated. It works pretty great, though I had to make my own feed tube modifications to get PLA to bend nicely and draw without kinking up. I think ABS would be perfect, but PLA is my target material. I'll just laser cut myself another one later...

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