Patent ID: 7770667

Claim:
A tractor for moving within a passage, comprising: a first body portion positioned along a longitudinal axis of the tractor; a second body portion positioned along the longitudinal axis of the tractor; a gripper assembly comprising: a gripper motor having an output shaft adapted to rotate about a gripper motor axis during activation of the gripper motor; a first gripper interface portion oriented substantially along the gripper motor axis; a second gripper interface portion in engagement with the first gripper interface portion, wherein one of the first and second gripper interface portions comprises a gripper rotating element configured to rotate about the gripper motor axis during rotation of the output shaft relative to the gripper motor, the other of the first and second gripper interface portions comprising a gripper extension element being configured to move longitudinally with respect to the gripper motor during rotation of the output shaft relative to the gripper motor, due to said engagement between the first and second gripper interface portions; and at least two elongated gripping elements engaged with respect to one of the body portions, the gripping elements having a movement-limiting mode in which the gripping elements limit relative movement between the gripping elements and an inner surface of a passage, and a movement-permissive mode in which the gripping elements permit substantially free relative longitudinal movement between the gripping elements and the inner surface; wherein the gripper extension element comprises part of a gripper expansion assembly for converting longitudinal motion of the gripper extension element into movement of the gripping elements between said movement-limiting mode and said movement-permissive mode of the gripping elements, the gripper assembly being configured to limit longitudinal movement of one of the body portions relative to the passage when the gripping elements are in said movement-limiting mode; and a power train assembly comprising: a power train motor; and a power train subassembly for converting activation of the power train motor into relative longitudinal movement between the first and second body portions.