Among other things, a connection assembly for motion along a rail is disclosed. The connection assembly can include a first plate assembly, a second plate assembly, and a release assembly. The first plate assembly can include a first stop mounted to a first base. The second plate assembly can include a second stop mounted to a second base and a post mounted to the second base. The release assembly can include a rod and a spring. The rod can include an outward extension. The spring can be disposed between the extension and the second stop. The release assembly can be configured to occupy: a first state such that the spring pushes the extension against the first stop and thereby biases the first base away from the second base; and a second state such that the spring pushes the extension against the post.