A caster assembly that includes a caster wheel, a lock member, a pedal, and a position sensor. The lock member can engage the caster wheel. Movement of the pedal towards a depressed position can cause engagement of the lock member against the caster wheel to resist or prevent rotation of the caster wheel. Movement of the pedal towards a released position can separate the lock member from the caster wheel to permit rotation of the caster wheel. The position sensor can detect a position of the pedal.

A wheel locking apparatus for locking the movement of a wheel assembly, said apparatus including an actuating means and a locking assembly. The locking assembly can include at least one locking arm. The actuating means can be configured to extend a locking arm from a first position to a second position. The locking arm is actuated into the second position to engage an aperture of the wheel assembly thereby locking the wheel assemblies. A locking arm having a locking pin portion that can be located at the second end of the locking arm. The locking pin portion can have a cavity wherein a portion of the locking arm fits within the locking pin portion. A biasing means can be located within the cavity and allow the locking pin position to move along a linear axis when a compressive force is applied to the end of the locking pin portion.

An autonomous transport vehicle, for transporting items in a storage and retrieval system, includes a frame, a controller, at least two independently driven drive wheels mounted to the frame, and at least one caster wheel mounted to the frame and having a castering assistance motor that engages the at least one caster wheel so as to impart castering assistance torque to the at least one caster wheel assisting castering of the at least one caster wheel. The controller is communicably connected to the castering assistance motor and configured to effect via a combination of vehicle yaw, generated by differential torque from the at least two independently driven drive wheels, and castering assistance torque from the castering assistance motor, castering of the at least one caster wheel with the autonomous transport vehicle in motion with a predetermined kinematic state.