Vehicle propulsion system

A human-powered vehicle comprising:

• a structural frame;
• a driven wheel having a hub mounted for rotation about an axle secured to a lower portion of the frame;
• a hand-operable crank rotatable about an axis disposed above the driven wheel and manually operable by an operator of the vehicle for vehicle propulsion;
• a transmission connecting the crank and wheel, such that motion of the crank is converted to a corresponding motion of the wheel;
• and
• a structural crank tower supporting the crank, the crank tower rotatable about the wheel axle and releasably securable to the frame to lock the tower in an upright position.

A vehicle comprising:

• a structural frame;
• a driven wheel having a hub mounted for rotation about an axle secured to a lower portion of the frame;
• a brake shoe that bears against a surface of the wheel hub to drive the wheel in one rotational direction for vehicle propulsion;
• a freewheel bearing that permits rotation of the brake shoe in said one rotational direction, and transfers braking loads to the frame while preventing rotation of the brake shoe in an opposite rotational direction;
• and
• a hub driver rotatable to drive the wheel hub in a first rotational direction, and to drive the brake shoe into torque-carrying engagement with the wheel hub to drive the wheel hub in a second rotational direction;
• wherein the axle is affixed to the frame on only one side of the wheel, such that the hub is cantilevered, and wherein the braking loads are transferred from the freewheel bearing to the frame through the axle.