Roller assemblies with selectively protruding fins

A roller assembly configured to mount to a drive shaft and to engage a target surface, the roller assembly comprising:

• a tube wall having a cylindrical shape and defining:
• an interior space radially surrounded by the tube wall;
• an exterior surface configured to contact a target surface and that defines an exterior surface diameter perpendicular to an axis of the tube wall;
• and
• slots passing through the tube wall from the interior space to the exterior surface;
• and
• a control surface assembly disposed within the interior space, the control surface assembly including fins aligned with the slots and adapted to selectively move between a retracted position contained within the tube wall and an extended position protruding beyond the exterior surface of the tube wall;
• and
• a fin actuator configured to selectively move the fins between the retracted position and the extended position;
• wherein:
• each fin includes a control surface configured to contact a target surface when the fins are selectively moved to protrude beyond the exterior surface of the tube wall;
• the control surfaces of the fins collectively define a circumferential control surface extending around the tube wall and adapted to contact a target surface from a plurality of radial positions around the tube wall in place of a portion of the exterior surface of the tube wall;
• the circumferential control surface defines a control surface diameter perpendicular to the axis of the tube wall;
• and
• the control surface diameter exceeds the exterior surface diameter by a variable amount based on how far the fins protrude beyond the exterior surface of the tube wall.