Mechanical linkage

A linkage system that connects an input shaft and an output shaft, the linkage system comprising:

• a first member having an input location fixedly connected to the input shaft;
• a second member having an input location pivotally connected to an output location of the first member;
• a third member having an input location pivotally connected to an output location of the second member;
• and
• a fourth member having an input location pivotally connected to an output location of the third member and having an output location fixedly connected to the output shaft,
• wherein a mode of operation of the linkage system is controlled by a device that moves the second member relative to the first member,
• wherein the linkage system has an engaged mode of operation whereby rotation of the input shaft causes corresponding rotation of the output shaft,
• wherein when the linkage system is in the engaged mode of operation, the pivotal connection between the first member and the second member, and the pivotal connection between the third member and the fourth member, are proximal to one another, while the pivotal connection between the second member and the third member is moved so that it is not collinear with the input shaft and the output shaft,
• wherein the linkage system has a disengaged mode of operation whereby the input shaft can be rotated independently of the output shaft, and
• wherein when the linkage system is in the disengaged mode of operation, the input shaft, the pivotal connection between the second member and the third member, and the output shaft, are collinear.