This week we modelled a soft-drinks can in SketchUp. A typical can is 135mm high and has a diameter of 66mm.
We made the model in two halves with overlapping edges that can be pushed together.
This model could be 3D-printed and used to hold components for one of our electronics projects. It gave us a feel for using SketchUp and designing our own models.
We drew a profile of one half of a can and extruded that profile around a circle to make the can. We included a lip on the inside of the shell in the profile. The detailed instructions to make the model are here.
One thing we discovered was that we need to delete the face in the circle, leaving just the outline, before extruding. If you leave the face intact, the extruded model will be missing its bottom face.
Then we made a profile of the other half, with a lip on the outside. We put the two together in SketchUp to see how they fitted. Section planes are helpful for this: insert a section in the vertical plane and move it in and out using the Move tool to see that the lips touch, but don’t overlap.
One ninja had a great idea: SketchUp allows us to apply materials to faces. So, he applied a glass texture to the model so that he could see through it and check that it was correct.
The method of drawing the profile in the instructions above is quite laborious. The intention is to give us an understanding of SketchUp’s inferencing system for drawing in a particular plane and snapping to end-points and mid-points. Our ninjas were able to construct the profile much quicker by drawing two touching rectangles, and then removing a section (to make the lip) with a third rectangle.
Next week, hopefully, we will try printing our models on the 3D printer to see how they look. Our 3D printer software needs a file in STL format to print. SketchUp doesn’t support STL out of the box. There is an extension in the 3D Warehouse that lets us export our model to STL, so we have to install that first.
This week we looked at colour and generating textures.
White light contains all other colours; we can see this when a prism splits it into a rainbow. A green object appears green because it absorbs other colors and bounces the green light back and into our eyes.
When we render an object in Blender, or any other 3D software, we want the renderer to generate the highlights (specular reflections) and shadow on the object. Any texture we use should be as free of highlights and shadow as possible.
To generate a relatively highlight and shadow-free texture of an apple, we used a pop-up portable photo studio. The interior of this box is white and reflective and lights the object relatively evenly on all sides.
We photographed the object, an apple in this case, at four angles around the circumference and once again for the top and bottom of the apple respectively. This left us with six shots of the apple from all sides.
I then opened each shot in Gimp (the image editing software), and removed as much of the rest of the image, everything that wasn’t apple, as possible. To do this I:
Used the Rectangle Selection Tool to select a box close in around the apple and then used Image | Crop to Selection to remove the rest of the image
Used the Fuzzy Selection Tool (aka. Magic Wand tool) to select white areas. I adjusted the Threshold value in the Tool Options panel as high as possible so that no parts of the apple were being selected when I clicked. I then used Edit | Cut to remove those portions.
Finally, there were portions of the supporting bowl that were still remaining. I used the Free Select Tool (aka. Lasso Tool) to select these and remove them.
Once I had each photo of the apple cleaned up, I created a new image, and pasted all the individual images into it, scaling them so that they were close to the same size. The result is here:
We also built a simple apple model by shaping a UV sphere. Next week we are going to stencil paint the apple model with this texture.
Hi Folks. Minimal notes this week as we spent the session working with the sculpting tools in Blender; something you really just need to try for yourself.
To start a new sculpting session, just choose File > New > Sculpting to be presented with a high-resolution quad sphere and an array of sculpting tools.
Of these tools there are three I find most useful:
Draw: Normally pulls out the mesh, but will create depressions when CTRL is held
Crease: Makes fine creases in the mesh. Great for adding detail
Smooth: Great for when the mesh has become a little rough or uneven
You should experiment with the others to see which you like best!
Finally, here’s a little rough and unflattering 10min self-portrait I knocked up at the end of the session, just for laughs:
When sculpting, it a good idea to remesh from time-to-time where you’ve significantly deformed the mesh. Remeshing evens the mesh spacing automatically, avoiding places where individual polygons are overstretched, but it’s only available in Blender 2.81. Some people had this version already installed, while others installed it during the session. If you haven’t got it yet and would like to install it you can get it here.
Finally, here’s little personal project you might like to see. I sculpted and painted my cat Noodle’s head. I used a couple of reference photos and a technique called stencil painting to generate the texture:
At CoderDojo Athenry, the Hackers spent some time examining the components of a desktop PC and a Raspberry Pi 3+ and a Raspberry Pi Zero.
Even though the Pis are much smaller than a desktop PC, they are functionally equivalent – as we saw, you can plug the Pi into the keyboard, mouse and screen of the desktop PC and use it like one.
We identified the major components of a desktop PC, and saw where each of them appear on the Raspberry Pi also:
CPU – the central processing unit that does all calculations and processing. All data in a PC gets represented as numbers, so all data processing ends up as calculations.
GPU – a dedicated processing unit just for graphics, that specialises in multiplying and adding matrices (pixels on a screen are represented as a matrix). Not all PCs have one, but they are important for high-performance graphics.
RAM – the short-term memory of the computer, used by the CPU to store data.
Hard Drive – this might be a hard disk drive or a solid-state drive. This is for long-term storage. It holds much more than RAM and the data remains when the PC is powered off, but it is much slower for the CPU to get data from the hard drive than from RAM.
DVD Drive – not all PCs have this. DVDs or CDs allow permanent storage that can be removed. Some are read-only and some allow reading and writing.
Motherboard – the circuit board on which everything else is mounted.
Power Supply – this is built into a desktop PC. For a Pi, this is a 5-volt supply such as a phone charger.
Networking – ethernet for wired networks and/or wifi for wireless networks.
Controller chips and connection ports (such USB and HDMI) for peripherals.
Case – Pis don’t always have these.
We noted that the Pi has a single chip that has its CPU, a basic GPU and up to 1GB of RAM all stacked in layers on top of each other. While its CPU is lower power than a standard PC CPU, it benefits from having a really short distance that data has to travel from RAM to CPU. CPUs run so fast that having electrons travel a few centimetres is a significant delay!
PCs and the Pi also have connections for peripherals, which is anything that can be connected to it, using USB, Bluetooth, HDMI, or other connection types:
Keyboard and mouse
The Raspberry Pi Zero has micro-USB and micro-HDMI connectors to keep everything as small as possible, and it has wifi only, no ethernet port (though it is possible to get a micro-USB to ethernet adapter).
A couple of members of the group have built their own desktop PCs, which is an impressive feat!