Not to be disheartened I read up on this format of RepRap and discovered to my dismay that it used Snap codes and not GCodes to communicate and it was about as old a Darwin as you could get without being one of the initial developers of the RepRap project (one of the very first purchasable RepRaps ever) it had been bought direct from Adrian Boyers group and therefore was a fairly standard Darwin (if there was ever such a thing) after spending a weekend tweaking the mechanics to make it a cube rather than a rhombus, and a few days of head wrangling (and a lot more web reading) I discovered the Snap Code issue (I had been trying to use the RepRap host software set to GCode rather than Snap code mode) a simple software switch later and it leapt into life (well it flashed some LED’s at me at least).
I had stripped the boards in an attempt to find out why the serial board did not seem to want to talk to the universal controller boards, that evening I wired it all back up to fire it up for the first time, initial impressions were good it seemed to be moving all axes and I was able to get the hotend "hotish" and melt some of the supplied albeit aged PLA.
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My first extrusion
Time for a test print, went straight for the Mendel corner bracket, and this is where things started to look not quite right.
After studying the plastic deposit closely it seemed like the machine was incapable of doing a diagonal line (i.e. it could only move 1 motor at a time) Much more web reading later (I was beginning to understand that this was going to be a trait of this project) and I discovered a hint of something to do with a missing sync wire! That evening I confirmed that the Darwin was indeed missing the sync wire, bodged one together and voila it "began printing" a very promising looking Mendel shaped part.
Failed Mendel Vertex (printed on generation 1 PIC based electronics)
Tried again, and again (each time tweaking the preferences file to see if I could improve the reliability) another few failed prints later and I was beginning to understand just how difficult it was going to be to make this beast reliable enough to do any useful work at all.
I seem to remember stopping when I broke the thermistor on the hot end after the umpteenth strip down to unclog the extrusion head again.
Bodged it back together, more failed prints later broke the nichrome, another hotend strip down, bodged back together again, more failed prints broke the Y axis (This was a temporary showstopper) after trying several ways of bodging this one I settled on a 1 inch piece of heavy duty petrol hose held on with 2 heavy duty hose clips as an impromptu Z motor coupling, this is working nicely and has remained there ever since.
So Z axis fixed (bodged) I continued with more failed prints, tweak settings, failed print (OK now this is starting to get boring) STOP and reassess!
The main flaws with the Darwin were as follows
1) Snap codes (outdated, new electronics set required)
2) New Z axis belt required (has been bodged/super glued after breaking)
3) Belt tensioner required
4) Very unreliable hot end (regular failures with both nichrome and thermistor wire's)
5) Very early and poor dc motor extruder design (geared stepper extruder required)
My attempted solutions to above issues
1) After much web reading (albeit not enough) I settled on a G3 based Sanguino set thinking that this would be the most likely compatible set for an old Darwin like this one. Bought 1.2 motherboard (discovered later that this was probably meant for a cupcake design and was prepped as so with ATX connector, RJ45 connectors, ATMEGA644 “not P” etc.)
2) Bodged Z axis belt with superglue after breakages.
3) Bodged the z axis with a solder sucker zip fastened to a lump of wood and zip fastened to Darwin frame to provide a very crude belt tensioner, the solder sucker is just serving as a nicely polished aluminium tube that I had handy.
4) After much more web reading, purchased Parcans hot end (nice looking design, and available on eBay)
5) My plan is to use the bits I have already purchased to get the Darwin printing and then as a matter of urgency print a geared extruder design.
I carried on with yet more failed prints in an attempt to get it going well enough to print an upgrade (geared extruder) but alas it was not going to happen.
By this point I had finally come to the conclusion that this beast was never constructed as a production machine but more a proof of concept (which makes sense as the students who built it were mainly interested in passing their degree’s).
So sadly the Darwin was switched off for around a month whilst I investigated what I needed to do to get the new G3 electronics set I had purchased to work.
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