One of the methods of developing artificial gravity in a ship traveling on interplanetary journeys lasting many months is to apply spin to the ship. Studies have shown a practical limit of this method to be that a rotational rate in excess of two rpm (revolutions per minute) will cause dizziness in the passengers. To counter this problem, several engineers have proposed dividing the ship into two parts: a crew section and a service module. A long cable would run between the two parts and they would rotate around a common axis. Using this method, if one were to limit the rotation to say 1 one and a half rpm, the longer the cable, the greater the sensation of gravity, the shorter the cable, the lesser the sensation of gravity.
To calculate how long the tether must be to generate a simulated gravity of one sixth G at one and one half rpm, you need only apply a relatively simple formula:
R = G / ((pi * rpm)/30)2
R is the radius of the circle described by the crew compartment expressed in meters and G is the desired rate of acceleration expressed as meters per second. After doing the math you arrive at a figure of 66.7 meters. That would be the approximate distance from the axis to the crew/cargo section. Since the axis of rotation is located at the center of gravity of the system, the service module would be either closer or farther from the center depending on whether it is heavier or lighter than the crew quarters.
Note: A portion of this explanation is taken from my forthcoming story: Ribbon to the Sky.