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Brake mechanisms for a wheel of non-motorized wheeled vehicle such as, e.g., a shopping cart, are described. In various embodiments, the brake mechanism can provide a variable amount of braking force or torque between zero and an amount sufficient to lock the wheel. In some embodiments, the brake me

Brake mechanisms for a wheel of non-motorized wheeled vehicle such as, e.g., a shopping cart, are described. In various embodiments, the brake mechanism can provide a variable amount of braking force or torque between zero and an amount sufficient to lock the wheel. In some embodiments, the brake mechanism includes a brake plate that is movable toward and away from a surface of the wheel hub along a direction parallel to the rotation axis of the wheel. The brake plate is configured not to rotate when the wheel and hub are rotating. Frictional engagement between the brake plate and the surface of the wheel hub provides the braking force. The brake plate and/or the surface of the wheel hub can include engagement features such as, e.g., protrusions and slots. In some embodiments, the brake mechanism fits entirely within the wheel.

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1. A brake assembly for a wheel of a non-motorized wheeled vehicle, the brake assembly comprising: a wheel hub comprising a side wall, the wheel hub having a hub axis that is substantially perpendicular to the side wall, the side wall comprising a plurality of first engagement features spaced transv

1. A brake assembly for a wheel of a non-motorized wheeled vehicle, the brake assembly comprising: a wheel hub comprising a side wall, the wheel hub having a hub axis that is substantially perpendicular to the side wall, the side wall comprising a plurality of first engagement features spaced transversely from the hub axis;a brake plate having a plate axis that is substantially perpendicular to the brake plate, the brake plate comprising a plurality of second engagement features spaced transversely from the plate axis;an axle that couples the brake plate to the wheel hub such that the plate axis is substantially collinear with the hub axis, the axle configured to allow relative rotation between the wheel hub and the brake plate, the brake plate axially movable relative to the axle between a first position and a second position, the first position spaced a first distance along the hub axis from the side wall and the second position spaced a second distance along the hub axis from the side wall, the second distance less than the first distance;a drive mechanism configured to move the brake plate between the first position and the second position, the drive mechanism comprising a rotatable drive gear, the drive gear comprising a drive feature configured to mate with a complementary drive feature on the brake plate such that rotation of the drive gear in a first direction causes the brake plate to move from the first position to the second position and rotation of the drive gear in a second direction opposite to the first direction causes the brake plate to move from the second position to the first position; anda spring configured to urge the brake plate into engagement with the drive gear such that the drive feature of the drive gear mates with the corresponding drive feature of the brake plate,wherein the plurality of second engagement features are configured to engage the plurality of first engagement features when the brake plate is in the second position but not when the brake plate is in the first position. 2. The brake assembly of claim 1, wherein at least one of the plurality of first engagement features comprises a protrusion and at least one of the plurality of second engagement features comprises a slot. 3. The brake assembly of claim 1, wherein at least one of the plurality of first engagement features comprises a slot and at least one of the plurality of second engagement features comprises a protrusion. 4. The brake assembly of claim 1, wherein the brake plate comprises a disc and one or more inserts coupled to the disc, the disc formed from a polymer and the one or more inserts formed from a metal, wherein at least one of the plurality of second engagement features is formed in at least one of the one or more inserts. 5. The brake assembly of claim 1, wherein the wheel hub comprises one or more inserts coupled to the side wall and at least one of the plurality of first engagement features is formed in at least one of the one or more inserts. 6. The brake assembly of claim 1, wherein the wheel hub is configured to rotate as the wheel rotates and the brake plate is configured not to rotate as the wheel rotates. 7. The brake assembly of claim 1, wherein the brake plate comprises a first retaining feature, the side wall of the wheel hub comprises a second retaining feature configured to engage the first retaining feature, wherein engagement of the first retaining feature and the second retaining feature permit relative rotation of the wheel hub and the brake plate. 8. The brake assembly of claim 7, wherein the first retaining feature comprises an annular groove and the second retaining feature comprises an annular ridge or the first retaining feature comprises an annular ridge and the second retaining feature comprises an annular groove. 9. The brake assembly of claim 1, wherein the axle comprises a first portion and a second portion, the first portion configured to engage the wheel hub and the second portion configured to engage the brake plate, the first portion configured to allow the wheel hub to rotate relative to the axle and the second portion configured to inhibit the brake plate from rotating relative to the axle. 10. The brake assembly of claim 1, wherein the drive feature on the drive gear and the corresponding drive feature on the brake plate comprise one or more arcuate ramps. 11. The brake assembly of claim 1, wherein the drive mechanism further comprises an electric motor configured to rotate the drive gear in the first direction and the second direction. 12. The brake assembly of claim 1, further comprising an electromagnetic receiver configured to receive one or more control signals, wherein the drive mechanism is configured to move the brake plate from the first position to the second position or from the second position to the first position in response to a received control signal. 13. The brake assembly of claim 12, wherein the drive mechanism is configured to move the brake plate from the first position to the second position in response to a lock signal and to move the brake plate from the second position to the first position in response to an unlock signal. 14. The brake assembly of claim 1, wherein the wheel hub further comprises a tire engagement surface configured to accept a tire. 15. The brake assembly of claim 1, wherein the brake assembly is configured for use with a shopping cart wheel. 16. A method of inhibiting movement of a non-motorized wheeled vehicle, the method comprising: providing a wheel comprising the brake assembly of claim 1; andmoving the brake plate of the brake assembly from the first position to the second position. 17. The method of claim 16 further comprising moving the brake plate of the brake assembly from the second position to the first position. 18. The method of claim 16, wherein the brake assembly further comprises an electromagnetic receiver configured to receive one or more control signals, the drive mechanism configured to move the brake plate from the first position to the second position or from the second position to the first position in response to a received control signal, the method further comprising: receiving at least one control signal and moving the brake plate from the first position to the second position or from the second position to the first position in response to the at least one control signal. 19. A wheel for a human-propelled wheeled cart, the wheel rotatable about a wheel rotation axis, the wheel comprising: a wheel hub comprising a cavity and a tire engagement surface configured to accept a tire; anda brake configured to inhibit rotation of the wheel about the wheel rotation axis, the brake disposed in the wheel hub of the human-propelled wheeled cart, the brake comprising: an engagement surface configured to rotate about the wheel rotation axis when the wheel rotates, the engagement surface disposed within the cavity of the wheel hub;a brake surface configured not to rotate about the wheel rotation axis when the wheel rotates, the brake surface movable toward and away from the engagement surface in a direction substantially parallel to the wheel rotation axis; anda brake actuator disposed within the cavity of the wheel hub, the brake actuator configured to move the brake surface between a first position and a second position relative to the engagement surface along the direction, the brake surface disposed within the cavity of the wheel hub when in the first position and when in the second position, wherein when the brake surface is in the first position the engagement surface and the brake surface are not in contact, and when the brake surface is in the second position at least a portion of the engagement surface and the brake surface are in contact, thereby inhibiting rotation of the wheel, the brake actuator comprising a rotatable drive gear such that rotation of the drive gear in a first direction causes the brake surface to move from the first position to the second position and rotation of the drive gear in a second direction opposite to the first direction causes the brake surface to move from the second position to the first position,wherein the engagement surface comprises a plurality of first features spaced transversely from the wheel rotation axis, and the brake surface comprises a plurality of second features spaced transversely from the wheel rotation axis, at least one of the plurality of first features configured to engage at least one of the plurality of second features when the brake surface is in the second position. 20. The wheel of claim 19, wherein a frictional material is disposed on at least a portion of the engagement surface, on at least a portion of the brake surface, or on at least portions of both the engagement surface and the brake surface. 21. The wheel of claim 19, wherein at least one of the plurality of first features comprises a protrusion and at least one of the plurality of second features comprises a slot or at least one of the plurality of first features comprises a slot and at least one of the plurality of second features comprises a protrusion. 22. The wheel of claim 19, further comprising an electromagnetic receiver configured to receive one or more control signals, the receiver configured to communicate with the brake actuator, the brake actuator configured to move the brake surface from the first position to the second position or from the second position to the first position in response to a received control signal. 23. The wheel of claim 22, wherein the brake actuator is configured to move the brake surface from the first position to the second position in response to a lock signal and to move the brake surface from the second position to the first position in response to an unlock signal. 24. The wheel of claim 19, wherein when the brake surface is in the second position, the wheel is not in a locked state in which rotation of the wheel is substantially prevented. 25. The wheel of claim 19, wherein the human-propelled wheeled cart comprises a shopping cart. 26. The wheel of claim 19, wherein the wheel has a diameter in a range from about 3 inches to about 10 inches. 27. A human-propelled wheeled cart comprising the wheel of claim 19. 28. The wheel of claim 19, further comprising a tire attached to the tire engagement surface of the wheel hub. 29. A brake assembly for a wheel of a non-motorized wheeled vehicle, the brake assembly comprising: a wheel hub comprising a side wall, the wheel hub having a hub axis that is substantially perpendicular to the side wall, the side wall comprising a plurality of first engagement features spaced transversely from the hub axis;a brake plate having a plate axis that is substantially perpendicular to the brake plate, the brake plate comprising a plurality of second engagement features spaced transversely from the plate axis,wherein the brake plate comprises a disc and one or more inserts coupled to the disc, the disc formed from a polymer and the one or more inserts formed from a metal, wherein at least one of the plurality of second engagement features is formed in at least one of the one or more inserts;an axle that couples the brake plate to the wheel hub such that the plate axis is substantially collinear with the hub axis, the axle configured to allow relative rotation between the wheel hub and the brake plate, the brake plate axially movable relative to the axle between a first position and a second position, the first position spaced a first distance along the hub axis from the side wall and the second position spaced a second distance along the hub axis from the side wall, the second distance less than the first distance; anda drive mechanism configured to move the brake plate between the first position and the second position, the drive mechanism comprising a rotatable drive gear, the drive gear comprising a drive feature configured to mate with a complementary drive feature on the brake plate such that rotation of the drive gear in a first direction causes the brake plate to move from the first position to the second position and rotation of the drive gear in a second direction opposite to the first direction causes the brake plate to move from the second position to the first position,wherein the plurality of second engagement features are configured to engage the plurality of first engagement features when the brake plate is in the second position but not when the brake plate is in the first position. 30. The brake assembly of claim 29, wherein at least one of the plurality of first engagement features comprises a protrusion and at least one of the plurality of second engagement features comprises a slot, or at least one of the plurality of first engagement features comprises a slot and at least one of the plurality of second engagement features comprises a protrusion. 31. The brake assembly of claim 29, wherein the wheel hub is configured to rotate as the wheel rotates and the brake plate is configured not to rotate as the wheel rotates. 32. The brake assembly of claim 29, further comprising an electromagnetic receiver configured to receive one or more control signals, wherein the drive mechanism is configured to move the brake plate from the first position to the second position or from the second position to the first position in response to a received control signal. 33. The brake assembly of claim 32, wherein the drive mechanism is configured to move the brake plate from the first position to the second position in response to a lock signal and to move the brake plate from the second position to the first position in response to an unlock signal.