This is a work-in-progress model of a robot leg consisting of two parallelograms (one for the upper leg, and one for the lower leg) with a separate lever to allow the lower leg to be actuated apart from the upper. It's completely from-scratch, but I used screenshots of the CB-20 robot (search on YouTube) by Yuhang Hu of Columbia University for reference.

When the leg is moved, the foot (mostly) remains parallel to the ground. When the upper lever is moved, the lower leg moves while leaving the upper leg unmoved. It's pretty near, but at the moment, this is a curiosity that only serves to demonstrate the basics of this style of leg. It's fun to play with, and the printable pegs go in firmly after a light tap with a mallet and help hold the leg in position.

The next step is designing a fixture for 3 LX-16A servos, then a way to rig two legs together. Eventually, we'll have a whole robot, in theory.

The harness takes the place of the “body” of the robot to fix the upper limb. The leg assembly has all the other parts, including a number of pegs which can be printed. You should have more than enough pegs correctly sized. I included a CAD file as well, and a gcode for a Bambu X1c which includes a few quality-of-life modifications, including slicing the bottom off some parts so they sit flat, supporting them, etc.

Updated files will be incoming as I modify them.