The YF-19: Solving the Bay Door Logic

After a full week of not too much progress, I can say I’m back in the game of rigging this baby.

I continued on with more Youtube tutorials, for example a steam-powered machine that rotated a wheel, using Inverse Kinematics. This was going to become a useful skill since many articulations in the YF-19 have piston hydraulics. So I practiced a little while and then went back to the project.


When I learned how to make bones and attach them to things, I also learned that I need controllers to move them around, without touching said bones. It’s a good habit, don’t touch the strings that move the puppet, but rather the wooden stick that holds them and moves them. Ok, so I started making controllers for the rest of the landing gear bay. And then I got stuck with this.

January 25 - Fixing bay doors

January 25 – Fixing bay doors

I don’t know if this image would be clear enough to explain what the problem was, so I’ll try to describe it: The bay doors are not in a straight angle, but a bit skewed in relation to the world, so there’s a small angle when they open and close in relation to the fuselage. That’s all nice and well since the bones can be also rotated to be perfectly aligned in relation to that axis. On the last post’s video of the landing gear deploying I just rotated the bones to make my animation, but now I wanted to make the controllers move the door.

The problem was, the controller is not a bone, but a regular object, and it can’t be rotated like a bone along its own axis, but along the world’s axis XYZ. If I made the controller also skewed like the bone, I could no longer rotate it numerically, since the numeric values are either X, Y or Z in the world. Rotating an object locally, that is, in a skewed angle, would change the three rotation axis values. That wouldn’t work since I wanted to be able to just rotate one axis, not the three of them at a time.

So how can I make the bone follow the controller, but on its own axis, not the controller’s? I gave it a long hard thinking. The bone couldn’t just follow the controller since that would make it rotate with it, on the world’s XYZ, and then the door would not open right.

The answer came with what I learned from IKs. The steam-powered machine had a restriction on the arms of the pistons so that they wouldn’t rotate on all axis. I could do the same thing with the door bones. So I put a locator so the bone could point to it at all times, then the locator was parented to the controller. The controller rotates, the locator rotates with it, the bone points to it while restricted to its axis. The bay door geometry is parented to the bone. Voilà!

It’s easier to show the result than to try to explain this. Play these images alongside 2001: Space Odyssey‘s opening theme:

Duuuhh... Duuhhh.. Duuuuuhhhh... Duhn duh duuuuuhhhh....

Duuuhh… Duuhhh.. Duuuuuhhhh………. Duhn duh duuuuuhhhh….!!!


About Eduardo

I'm some dude with a huge love for animation and film. I've been working in TV animation for the past 6 years in New Zealand. I love dragons, pointy metal things that can cut dragons, and flight simulators.
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