The Automatic clutch appeared in Meccano Magazine in November 1931.
Its operation is very simple. As the clutch gathers speed the centrifugal force causes the Collars 59 to fly outward and so make contact with the rim of the Wheel Flange 137, ensuring drive to the model. If the motor detects resistance, the Spring Cord attatched to the Collars will take over and disengage the drive.
This mechanism is particularly useful for driving heavy models, where a slow start is more desireable, and so giving realism to the model.