Semester Project 2015/2016

Crystal Generator

Write an OpenSCAD module crystal that adheres to the prescribed interface and displays/creates a crystal based on input data.

module crystal(thorns=[]) { ... }

The vector (array) thorns contains definitions of individual outgrowths (spikes) from the crystal. One spike is defined by rotation, length, radius and number of segments.

thorns_abstract = [[[rotx, roty, rotz], height, circumr, seg], ...];
thorns_example = [[[0,0,0], 30, 3, 4], [[90,0,0], 25.5, 2.65, 7]];

Each spike has a shape similar to this image (image can be enlarged):

The center of the bottom side lies at the coordinate origin. Before rotation, the spike points straight up (along the positive Z axis). The total length of the spike is height, the break is at the cube root of height from the top. The spike has a profile of a regular ("equilateral") n-gon, where n is seg. The circle circumscribed around this n-gon has radius circumr at the break, and at the bottom of the spike the radius is one-third. The spike is then rotated by the vector [rotx, roty, rotz].

The crystal is just a mixture of these spikes.

For the given two-spike example, the result looks something like this:

Another task is a module generating random crystals. So it doesn’t receive specific data as input, but only their bounds (closed intervals) and the number of spikes.

module random_crystal(nthorns=350, rot=[-90,100], height=[20,40], circumr=[2,4.5], seg=[3,10]) { ... }

For generating random numbers you can use the rands() function. Keep in mind that seg is (unlike other random values) an integer. Individual integers including edge values should have equal chance (uniform distribution), be careful, failure to do this will incur point deductions.

For default values the crystal can look different (it’s random), for example like this:

Your Crystals

Each of you has been assigned three randomly generated crystals. You have them available both as data for the crystal() module and as STL files. It’s possible that your data will render too long in OpenSCAD using F6. That’s okay, that’s why you also have the model in STL format. To test the functionality of the module, you can use a subset of your data - verify that the module behaves according to the specification.

If you still want to test your module with your assigned data, test it only in Compile mode (F5) and if there are problems, significantly increase the Turn off rendering at value in OpenSCAD settings.

You can find your crystals at these addresses:

Where instead of XXX you substitute digits from this list:

removed

Preprocessing

Choose any (in your opinion the easiest) of your three crystals and prepare it for printing. You can do practically anything with it (fix, rotate, cut, add support structures), but it is necessary to preserve the crystal’s dimensions and shape during printing. The output is one or more STL files ready for slicing and a very brief description of what you did and why (not necessarily in writing, but during submission it is necessary to explain the process and this even several weeks after making your changes).

Slicing

Slice your prepared print STL with any program using appropriate settings. For Slic3r, start from slic3r-config-bundle.ini.zip (select profiles as in the exercise, i.e., not -default-). We don’t have profiles for other programs for you, but you may create your own. The output is the used slicing profile exported from the program and one or more GCODE files. Individual parts can be printed at once (if they fit on the print bed and if it seems appropriate to you) or sequentially, or a combination of both.

Printing and Postprocessing

In credit events listed in KOS, taking place during the examination period, you will be printing crystals from ABS in the laboratory from your prepared GCODE files. After printing is complete, the print must be properly processed - remove supports, glue together, etc. The resulting crystal should look as similar as possible to the required model. One term has a maximum of 5 hours total (printing + postprocessing).

In case of absolute failure during printing, it is possible to repeat the print with a new GCODE, but only once. In case of a technical problem on our side, this does not count as a wasted attempt, of course.

Submission, Grading and Deadlines

Upload a zip file of any suitable name to your namespace on Edux, with a link to it from your namespace. Include all written descriptions directly in your namespace on Edux.

Submit in the file:

The submission deadline is June 19, 2016 inclusive (or the beginning of your credit term, if it takes place earlier). Possibility of late submission: For each additional started week (even by a second) 10 points are deducted from the total grade. If the total sum is less than 0, the grade for the semester project is 0. At the time of commencement of the classified credit term (printing in the laboratory), it must already be submitted on Edux.

The examination period ends July 1, 2016, we have nothing against submission and credit terms even after this date, but it is necessary to explicitly agree on this and accept the risks arising from it.

Grading according to the following table:

Grading is divided into 4 sub-sections. Mandatory within the section means that without completing this task the student will not receive any points for that section. In case of remedial printing, values of points in other sub-sections are no longer corrected. So if for example you fail slicing, you get zero points for it and (quite logically) the print also fails fatally, you can get points for printing in a remedial term, but you won’t get any more points for slicing.