Abstract: Disclosed are assemblies, systems, devices, methods, and other implementations, including an assembly that includes a moveable mechanical structure (e.g., a lever), and a gate to control movement of the moveable mechanical structure. The gate include a rotatable body, and at least two appendages extending from the rotatable body, including a first appendage configured to stop rotational movement of the gate in a first direction beyond a first angular position when the first appendage contacts a blocking structure, and a second appendage configured to contact the moveable mechanical structure that, when the moveable mechanical structure contacts the second appendage, actuates the gate to cause rotation of the gate.