Disclosed inventory systems, methods, and devices can be used to retrieve and transport resources from one location to another. Specifically, a vertically mobile drive unit including a vertical element retention mechanism can be controlled by a management component to retrieve a resource, transport the resource from one floor to a different floor in an inventory system, and deposit the resource at a destination. The vertically mobile drive unit can transit vertically along a vertically disposed element in an inventory system, such as a structural pole or column. The vertically mobile drive unit can ascend to or descend from an upper level by passing through an opening made by a movable panel.