One of the highlights from World Maker Faire 2013 in NYC was meeting Thingiverse All-Star cerebus333. He’s friendly, engaging, and incredibly prolific; I can’t recall a week’s recent passing where he hasn’t posted at least one new model to his collection.
I was honored to take home an autographed Rock Frog from Cerebus’ collection, and I promised him that I’d take a shot at remixing his work when I got back home. Here’s the original model, standing about 7 inches tall.
Cerebus has designed the Rock Frog to print reliably on an FDM printer, and print reliably it does: the mesh is manifold and it’s physically quite stable on the build platform. My plan is to re-pose the original and turn it into something usable as an RPG elemental or golem miniature, and that’s going to require some geometry edits.
Cerebus designed the Rock Frog’s knuckles to lay flat on the printing bed. If they’re going to potentially be raised up in the air they’ll need to look more like fingers. I’ll delete the old flat surface and replace it with some vaguely-knucklelike ridges. A little sculpting here and there and we’ve got something that looks good enough for now– my experience with 3D printing tells me that much more detail here isn’t going to print at this scale so there’s not much point in overworking the model.
Note the strange triangulation in the sole of the foot, because I’ll fix that in step 2.
I’ve split him in half down the YZ axis so I only have to fix one hand before mirroring and rejoining the model.
The foot geometry is fine for printing, but not so good for deformations. This should be a straightforward fix, and afterwards Rock Frog will be able to put some weight on the ball of his foot.
Rock Frog’s mouth is closed in the original. I’ll find the inside crease of his mouth, split the geometry, and then open up his mouth. A note for folks not used to working with character models; it’s generally easiest to work on one half of a model and then mirror it, which is why the original Rock Frog has been split down the middle here.
Bipedal 3d characters are usually modeled in T-Pose, with arms outstretched. This pose helps when assigning weights to vertices, step one in rigging a character. I’m not going to invest a lot of time in a full animation rig here, just enough to intuitively bend Rock Frog at his joints.
Rock Frog’s legs are already in a good position for vertex assignment, so no adjustments need be done there. Once I’ve got him in T-pose I’ll inspect the mesh one more time to make sure the mesh is closed and manifold.
If you’d like to pose Rock Frog on your own, go ahead and download the t-posed model.
I reach way back into the mists of time for inspiration, back to a time when Xiao Zheng was a fifth grader surreptitiously poring over the 1st Edition AD&D monster Manual under the covers. I move some joints around here and there until Rock Frog more or less resembles David C. Sutherland III’s classic drawing of an earth elemental, with allowances made for the gravity-plagued medium of supportless FDM printing.
The posing created some self-intersecting geometry where I didn’t bother to weight the vertices properly. Bad mojo. I can easily fix this by painting the vertices with a smoothing algorithm, but doing so while the model’s rigged to joints can be slow and produce unpredicatble results.
At this point it makes sense for me to detach the geometry from its joints, freezing Rock Frog in this position. I’ll save a version of the rigged model in case I want to re-pose him later.
And now a test print. Almost everything prints OK, but the heel of his right fist hangs out in space just a bit too much. Frankly I should have seen this coming. Part of the problem is that I’m printing at a .3mm layer height for the test, but there’s just too much overhang there even with a higher-resolution print.
The model’s now detached from its joint system, so if I’m to edit that fist I have to do it without the benefit of a weighted joint system. This is a small tweak, so I just throw a lattice around the fist and forearm instead of backing up to the beginning of step 5.
The fist on the second print looks much better, so I’ll go back and add some aesthetic tweaks. I’d like to roughen up the surface with some stony protrusions. Much of this can be done with Maya’s poly sculpting tools, but I add some nicely geometric gems for contrast too.
The gems stuck in the Rock Frog’s back are easy to model but they don’t retain their sharp geometry in the final print. I’d like to see how this prints at a higher resolution.
This model and others like it are of course available for free download in The Forge. This post is the first in my series of Maker Faire Gems, wherein I’ll be blogging interesting stuff I discovered this year that might have slipped through the bigger outlets’ coverage. #staytuned