An autonomous modular robot includes an attachment retention system that for retaining two or more interchangeable attachments for performing unique tasks, e.g., steam cleaning, vacuuming, grass cutting, etc. The attachments may be sequentially positioned in the path of travel of the robot and configured to perform complementary tasks. For example, for cleaning a floor, a first attachment may be configured to vacuum the floor and a second attachment may be configured for steam cleaning the floor. The robot may also include a vertically translatable lift mechanism. The lift mechanism may include the attachment retention system, thereby allowing the attachments to be moved vertically. The lift mechanism may also include a dimension sensor proximate a top of the lift mechanism. The dimensionsensor may be utilized to determine the size, e.g., a height and/or a width of the robot with any retained attachments, to help navigate the robot and avoid obstacles.
