The present disclosure discloses a wheel assembly structure and a child activity center. The wheel assembly structure includes a connection base and a wheel assembly that is deployable. The wheel assembly is pivotally connected to the connection base. The wheel assembly has a deployment state and a storage state. An adjustment mechanism is provided between the connection base and the wheel assembly. The adjustment mechanism is configured to switch the wheel assembly into the storage state from the deployment state. When the wheel assembly is in the deployment state, the wheel assembly is deployed to a first position to move the connection base. When the wheel assembly is in the storage state, the wheel assembly is stored to a second position to stably place the connection base. The wheel assembly structure has a simple overall structure, which facilitates production and lowers production costs.

An autonomous delivery vehicle having one or more caster wheels that may be held off the ground for a portion of the time that the autonomous delivery vehicle travels. Each caster wheel is mounted in a pivot with a centering mechanism to hold the caster wheels in a design orientation. The caster wheel in the design orientation maximizes the view of forward-looking sensors on the autonomous delivery vehicle. The centering mechanism uses a compression spring that drives a follower and swashshaft to apply a rotation force on the caster wheels. The rotational force urges the casters frame and wheels to return to a design position. The rotational force increases with the rotational difference between the caster rotational position and the design position.

A caster with horizontal braking includes a connecting base, a wheel rotatably connected to the connecting base, and a brake assembly including a movable plate slidably connected to the connecting base and a rotary plate. The movable plate is provided with a brake pad at an end and a first abutting plate with a limiting portion thereon, and is rotatably connected to the connecting base. A second abutting plate fitted with the first abutting plate is arranged on the rotary plate. When the rotary plate is rotated to cause the second abutting plate to push the first abutting plate to move backward, the brake pad moves backward to abut against the wheel, one end of the second abutting plate is abutted against the limiting portion, the force applied by the wheel to the brake pad opposites the force applied by the second abutting plate to the limiting portion.