As you all know, my brain does not work like that of normal people. [He says, making a grotesque understatement.] One particular gift/curse granted me by this derangement of the mind is my innate ability to just mentally disassemble things I’m looking at, and—regardless of complexity —instantly understand how they work.  Or, to put it another way: I can see the Matrix.

So I was doing my morning web browsing, when I spotted an article about an animatronic attraction being constructed at Tokyo Disneyland. The animated gif heading the article caught my attention because the technology looked so advanced. And in the video, they showed the inner workings of one of the characters’ arms for like three seconds. Read on for a better look at the arm, and my (over)analysis.

The Animatronic Arm

Yes, I really did capture three frames from the video and stitch them together to get this pic. No, I am not right in the head.

My (Over)Analysis

They’re clearly not screwin’ around here, these ain’t some hokey old animatronics made out of welded steel, pneumatic cylinders, and fiberglass… That is some beautifully CNC-machined and anodized aluminium. Some real aerospace-grade engineering and design work, to be sure. I’m guessing the plastic is SLS nylon. Both for the material properties and because an SLS printer is a perfect fit for the in-house rapid-prototyping and production needs of an operation like this. 🤔

As an enginerd and maker-of-things, I am in awe of this. All I do is sit around designing crazy stuff, and even I’m learning things just from looking at that picture!

Take for example the wrist articulation. It has a deviation (side to side) axis driven by a servo in the forearm, connected via a linkage across the wrist joint, to a pivot. (That’s why there’s two pivots. The other, central, one is the pivot where the hand is connected to the arm.)

Except I’m almost certain the wrist also has a flexion (bending) axis as well. There’s no other reason for the wiring harness to continue on into the hand unless there’s a servo in there, moving the wrist on what appears to be a pivot perpendicular to the other two pivot points… Which would mean that both the linkage for the deviation axis, and the main pivot for the wrist, aren’t attached to the hand itself, but to a stationary part of this additional axis. (Because they have to be fixed, and not bend with the hand.)

[Edit: The more I look at it, the more I’m not completely certain the deviation axis is moved by a servo. If it’s a servo, it shouldn’t be necessary to physically restrict the movement, as you can see on the forearm end of the linkage. Unless that’s just a failsafe. I wouldn’t think any of it would be pneumatic though, traditionally pneumatics aren’t responsive enough to get these kinds of performances.🤔 I also have yet to figure out where the actuator for the flexion axis is, or how it’s connected. One thought is that it’s either a hollow bore or double-shaft servo, and the flexion axis’ stationary pivot is attached to the shaft, while the motor is mounted to the hand. So the motor is the thing which moves, not the shaft.]

[Edit2: I did not know that pneumatic servo rotary drives were even a thing.🤨 Looking at the elbow, it’s entirely possible that they are employed here. I imagine they have much finer control than traditional pneumatic actuators like pistons. I wonder what their holding-torque to size/weight ratio is versus regular electromagnetic steppers and servos.🤔]

*sigh* [Opens Fusion 360 and creates new project file]

The exterior is also quite impressive. I wonder what the material is they use… From the facial animation, it looks fairly flexible. But other evidence suggests maybe not that flexible?

They seem to use clever costuming to make sure you never see Belle’s elbow joints—telling me they’re either not covered, or the covering does something unsightly during acute bends —and clever tricks of animation and body language to make it seem like her neck has more range of motion than it does; By my estimate she can only turn her head +/- 15 degrees at most—less than a quarter a human’s range, nevermind an animated character, often employing exaggerated motion —so they turn her whole body to give those subtle head movements a wider arc. I didn’t even notice at first. I figure the limited range of motion is probably an issue like the elbow; any more and the outer covering material does something unsightly, except unlike the elbow, they can’t just hide it. I doubt it’s due to the complexity of the mechanics in the head, the wiring harness running up there shouldn’t be that extensive. (Plus there’s special wire for situations like this; rated to withstand being seriously bent in millions of operations in a piece of machinery.)

I’m quite interested in the software side as well. Looks like they’re animating the actual animatronics in Maya, not just doing a previz animatic or something. Did they also model the characters’ external appearances in Maya? (Or maybe 3ds Max?) I wonder how deep their Autodesk workflow goes… Are the inner workings designed in Fusion 360 and/or Inventor, or do they use a different CAD package, like SolidWorks? 🤔

I wonder if they outsource the machining work on those aluminium parts, or if the park has a ridiculous Mori-Seiki VMC or something in the machine shop, for maintaining the attractions… (At the very least they send the parts out for anodizing. You don’t get a finish like that under anything less than proper industrial conditions.❤)

tl;dr: This whole thing is quite the feat of engineering, made possible by the work of what are clearly some very smart and talented people, pretty much for the sole purpose of entertaining children. (Not saying that’s a bad thing, just framing it with my usual sarcasm to make sure we all recognize the overall absurdity.😂) And I have SO. MANY. QUESTIONS.

Anyway, there goes my whole damn weekend. I’m gonna go design a model of this arm I can 3D print and drive with hobby servos, because nothing says “World-Class Enginerd” like having a functional robotic arm just sitting on your workbench for giggles.

Because I can.