Monday, July 09, 2007
Lamarckian evolution at work... :)
I created a 2cm cube in AoI to use as a test object for printing - it's big enough that you can see what's going on (and what is going wrong), yet small enough that it doesn't waste too much material. Below is a picture of several stages of troubleshooting the printing parameters and software while printing the 2cm cube, as well as two rather laughable attempts at a minimug:
The square-and-blob at the far left is an example of what happens when you try to print at an angle with the current software if your XY speed is set in the high range (as it is when repstrapping using threaded-rod drive for the X and Y instead of belts - my XY speed is set to 244). Since the speed setting is not very linear at the high end, when the software adjusts the speed to account for driving the head at an angle, it tends to slow the motors down far more than intended, and you end up with puddles instead of nice pretty lines. I have created a quick fix for this in the software, but since it is only necessary for repstrap machines that use threaded rod for the X and Y axes (Darwin uses belts) and Adrian mentioned fixing the non-linearity of the speed settings at some point, I won't be providing the fix as a patch into the main code unless asked. If any of you decide to repstrap using threaded rod for the X and Y, please feel free to contact me and I will help you add the fix into the software for your setup.
The second square in the series is a good example of what happens when the extruder feed is too fast and the head is too close to the table - it's kinda hard to see in the photo, but instead of nice distinct lines, everything is a bit smeared.
The next squares in the series show the progression as I tweak the various settings - getting the initial Z position of the extruder to the right spot, adjusting the extruder speed, and getting the layer height right.
The minimug attempts at the top of the picture were done partially to see what would happen, and partially because I had not done more than a few layers at a time yet, and wanted to know what changed or went wrong ten layers up or so. The rather wobbly extrusion you can see at the upper left of the short mug is a result of the layer height being incorrect - as the layers progress, the extrusion head is placed farther and farther away from the object being printed, and the plastic just goes everywhere. The 'lacy' look of both mugs is partially due to the extruder head height, and partially due to an apparent bug in the software that causes it to pause between sections of a circle as it is being drawn - the extruder is extruding too fast for the XY movement, and since the head is a ways away the thread tends to wobble back and forth. The threads that are crisscrossing the hole in the middle of the mugs are due to the head moving from one side to another when starting on the next layer - the CAPA tends to leave a long string behind, but this is quite easily cut away after the extrusion is done.
Below is a closeup of the rightmost test cube:
As you can see, it is looking a lot more like an organized extrusion. It is about 10 or 11 layers, and I am quite happy with the infill, and the outline extrusion is much closer to what I want to see. Unfortunately, I have a bit of drift in the Y axis (you can see the effects in the leaning of the minimugs), but hopefully I can clear that up by adding some oil to the Y slide - it's a bit stiff in a few spots, and I think it is making the Y motor skip a step or two here and there. Hopefully I can get the Y axis drift sorted out in the next few days, and I'll be drinking a toast with a new minimug!
If you need a bit more torque on your y-axis you could mod the firmware to drive two coils at a time instead of one. That is the more usual way of driving steppers. I think it gives you about root 2 times more torque at the expense of a small reduction in positional accuracy, and more heat of course.
i feel like it might be a good/fun idea to setup a RRRF bounty to whoever prints off (and ships) me a set of working parts for the extruder and/or the cartesian bot.
Zach - Oooh! A bounty! Sounds good to me! :)
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