A1 is Unitree’s original compact research quadruped — small and agile enough to carry by hand, and still a common reference platform in legged-locomotion academia even as Unitree’s own lineup has moved on to newer models.
The mechanism
Each of the four legs carries three actuated joints — a hip abduction joint, a hip flexion joint, and a knee — giving twelve degrees of freedom in total. No mimic joints or closed kinematic loops anywhere in the description, so this is a direct, unadjusted read of the URDF’s actuated joints.
About this file — read before importing
This links directly to
unitree_ros’s a1_description package,
Unitree’s own repository. ARMOR links directly to that repository rather than re-hosting
anything, so what you get is exactly what Unitree publishes, unmodified.