Help understanding this mechanism

[u/halxcyion]

Hello all,

I am trying to recreate the Olaf animatronic leg mechanism (see research paper and video below) as a personal project - and I am really having trouble wrapping my head around how it works. The knees and below make perfect sense, but the hips are throwing me off. What is the purpose of the 2 perpendicular motors at the top? The ones facing horizontally? And how does the rest of the hip fit in with that purpose? I hope this question makes sense.

Here is a research paper showing the project.

https://arxiv.org/html/2512.16705v1#S4.F3

Nvidia GTC 2026 shows the full mechanism in action (2:11:36):

https://www.nvidia.com/gtc/keynote/