New Pokémon content: Pokeball Ceramic Coffee Mug!
This is actually the project that was giving me such problems the other day, and it's probably worth talking about why those problems came about.
If you've been doing any degree of 3-D modeling or you have interest in it, you know that a lot of the time you look at something and then try and reproduce something like that as your model. In my case I do a lot of modeling which involves mimicking digital assets. In this case, a Pokeball. But there's a strange thing about digital assets that have been presented in multiple media, multiple forms, and which there are multiple ways to approach; you know less about what they look like to make one then you know about what they look like when you look at one.
I originally started out with a very naïve design for the Pokeball which became part of this cup. A simple revolute to create the ball along with a little notched cut out, another straightforward revolute to cut out the little space around the button, and everything's easy and straightforward, right? Well – no. Not really. Getting the little cut out band as part of a revolved sketch was very easy. Creating an orthagonal sketch to to a completely different cut which was intended to match up with the surface of the notch turned out to be a lot more complicated, in part because for some reason the sketch kept wanting to have a flat surface as its recess, and when you look at pictures of Pokeballs you realize that the area around the button is both curved and narrower than the larger band.
And that's if you remember up front that there is a button on the front of the thing in the first place. Which I did not.
That led me to completing what I thought was the basic design and staring at it, wondering what was wrong. Something felt wrong. Something was observably wrong. It took a good 10 minutes to figure out that I had completely left out the button. Then when I went with a naïve approach to actually modeling it as a single or pair of revolutes around an axial line running to the front of the sphere? The cut out wouldn't conform to the surface that I wanted; it was difficult to get the curves to match, even though I seemed to be approaching it in a perfectly reasonable way.
Now, I could have continued banging away on the same problem for hours and made no headway. But I found that the easiest way for me to make my way through a problem, an issue that is fighting me, coming up with a methodology for solving a problem I didn't even know I had, is to set it down, walk away, and come back later – whereupon I will probably sit down, pull up the tools, and the problem will immediately present itself if it hasn't already gelled in the back of my head during the time I was actively not thinking about it.
In this case, the solution was surprisingly obvious, just as much as it was intuitively perverse. As a person, I don't normally think of objects which occupy the same physical space as a reasonable thing to consider. After all, that's how you get massive antimatter explosions. But within the context of a parametric modeler, it's perfectly reasonable to have two volumes which occupy the same space, especially if you intend to carve away at one of them and leave the other unmarked. So that's what I did here, started by making two revolutes, one which represented the inner core of the Pokeball and the other which represented the outer shell. That made thing surprisingly easier to deal with. When I cut the trench, I could be very specific about going beyond the bounds of the revolute without worrying about whether I was going to be leaving a tiny surface layer because of the approximation of circle drawing in the application. I also knew that it was impossible for me to cut too deep – because there was a second object within which would be unaffected by the carving.
The same effects made cutting out the hole in the surface sphere just as easy. I knew that the bottom of the cut would be perfectly spherical because of the inner sphere and I knew that I could extend up beyond the surface of the outer sphere just a little bit and never have to worry about leaving accidental surfaces. There was one tiny stumbling moment when I was confused that the button cut was only appearing in the top half of the Pokeball, not the bottom half – and that lasted for about 45 seconds until I realized that the revolute cut had separated the top and bottom of the Pokeball outer shell into two literal shells which were bodies that needed to be included in the affected revolve which cut out the space for the button.
The rest of that was straightforward. Put the things together, use a Boolean unification to make them one object, and the Pokeball was done.
Making a coffee mug body is trivial. You make a rectangle of the right dimensions, you revolve it around the Z axis, and you have a coffee cup cylinder. If you stick a Pokeball on the front of it, extruded through the surface you can then run a Boolean union on the two and have a mug with a Pokeball growing out of the side.
And that's where things get interesting.
If the ball is solid, that's a lot of mass on the front of the mug. A very large amount of mass.
You may have noticed that we have not actually made the mug capable of holding a liquid yet, and that's why. Apply a Shell function to the top of the mug which is now one body with this ball on the front. In this case, I set the thickness of the shell to 6 mm, which is what Shapeways suggests as the appropriate thickness for an unsupported wall as large as it will print. You'll notice that the inside of the Pokeball surface gets hollowed out as well, which makes sense – it is one part with the mug body. Now you have a considerably lighter decoration on the front of the mug – and you know from having seen a mug or two in your life that there will be a handle on the other side which will help counterbalance the center of gravity of the mug when it's being used.
Before you start working on the handle, make sure to drop a little chamfer around the bottom of the mug as well as a bit of a radius fill it around the top. The chamfer will make it a little bit easier to not be banging the sharp corners of the mug on the desk or table every time you set it down. The fillet will make it much more pleasant to drink from the mug, rounding it for your lips. Don't forget that you should probably at least chamfer if not fillet the interior radius of the inside, bottom of the mug where drinks will sit. There's nothing worse than a dirty coffee mug where coffee grounds have stuck in that sharp edge of an un-filleted, un-chamfered mug bottom. Save someone, perhaps yourself, the trouble by making it much harder for stuff to stick in the corners. Remove corners.
Now you've got a handle to design.
My personal feeling about handles is that they are a complete pain in the ass to design. They are simultaneously curved and require smooth surfaces – but not too smooth or the user can't keep a good grip on it. In this case, I also wanted to be very precise about how much mass went into the handle in order to offset the mass remaining of the hollow ball at the front of the mug. In fact, having a little more mass toward the handle would help centralize things when the level of fluid in the mug was up over the level of the interior of the Pokeball.
Let me be frank: neither Onshape nor Fusion 360 makes working with centers of gravity any fun. I feel vaguely gratified that they provide the means of determining the center of gravity for any given body; that makes it possible. But neither one will actually put a point which represents the center of gravity of your volume which you can then use in making constructive geometry.
Here's how I did it.
First, get the CoG information. It will be expressed as an XYZ offset.
Make a sketch on the XY (bottom) plane. Put a single point on it. Set the dimensions of that point from the 0, 0 origin, because that is the core of the offsets that you've been given.
Create a plane, offset from the origin plane by whatever the CoG Z offset is.
Create a sketch on this new plane with the point from your first plane Use/Projected in. That is your center of gravity.
Now, go tinker with the design of your handle. Create a line which will act as the central sweep for it. Create a sketch of the profile you want to sweep along it. Decide you don't really like the center part of it, split the body at an offset above and below the center of gravity, cut out the middle, move some of the faces which result, at another sketch where you outline a change in the profile, do a loft from the surfaces that you cut to this new shape, apply fillets as the mood strikes you, and then look at your results. Maybe you like it. Maybe you don't.
Merge the handle with the body of the mug and regenerate the center of gravity info. Modify the offsets of the point and plain that you created for center of gravity calculations appropriately. Look at where the point ends up. Is it where you want it? Does the handle need to be thicker, heavier? Does it need to be lighter?
Iterate as necessary.
In this design I'm still not completely happy with the way that the balance ended up, though it's one of those situations where if you have to fall on one side or the other, it's probably better to have the weight a little toward the handle which is where the hand and all the leverage is going to be.
If this is been interesting to you or you want to have one of these mugs for your very own, I am selling them on my Shapeways store:http://shpws.me/MBCf
While they do not come in a full-color Pokeball version, you can get one in red or blue, if you are Teams Valor or Mystic. (My own team, Instinct, will just have to get by with white or black. Shapeways does not yet provide a yellow glaze for their ceramics.) If you have a heavy duty Pokémon player in your family or immediate circle, this is the sort of thing that you would like to get. If that person annoys you, this is the sort of thing that you would like to get to throw it.
I just want to cover all the bases.
Should you have enjoyed this discussion of 3-D modeling and coffee mug design, give us a Like, a +1, share this with your local community or friends, or ask any questions that you might have. I am available for commissions if you have something that you would really like to have in your hot little hands.
Thank you for your time and attention!