Autonomous transport vehicle with steering

An autonomous transport vehicle for transporting items in a storage and retrieval system, the autonomous transport vehicle comprising:

• a frame;
• a controller;
• at least two independently driven drive wheels mounted to the frame;
• and
• at least one caster wheel, of a non-holonomic steering system, is 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;
• wherein the controller is communicably connected to the castering assistance motor and configured to effect, via castering assistance torque from the castering assistance motor assisting castering input from vehicle yaw generated by differential torque from the at least two independently driven wheels, substantially scrubless castering of the at least one caster wheel with the autonomous transport vehicle in motion with a predetermined kinematic state.

An autonomous transport vehicle for transporting items in a storage and retrieval system, the autonomous transport vehicle comprising:

• 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;
• wherein the controller is communicably connected to the castering assistance motor and configured to effect castering of the at least one caster wheel with the autonomous transport vehicle in motion with a predetermined kinematic state 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, the castering assistance torque being developed substantially negating resistance from castering scrub in each predetermined kinematic state of the autonomous transport vehicle.