Magnetic throttling and control: magnetic control

An apparatus comprising:

• a platform configured to be magnetically coupled to an object disposed within a body cavity of a patient through a tissue, the platform comprising:
• a first magnet having a first end, a second end, and a first longitudinal axis extending through the first and second ends, the first magnet further having a first direction of magnetization;
• a second magnet having a first end, a second end, and a second longitudinal axis extending through the first and second ends that is parallel to the first longitudinal axis, the second magnet further having a second direction of magnetization opposite the first direction of magnetization;
• a platform member coupled to the first magnet and the second magnet;
• and
• a third magnet having a substantially rectangular cross-sectional shape in a plane that is substantially parallel to the third direction of magnetization, the third magnet disposed between the first and second magnets and having a third direction of magnetization that is fixed relative to the platform member and more perpendicular than parallel to each of the first and second directions of magnetization;
• where the platform is configured to permit the third magnet to be moved relative to the first and second magnets, in a direction parallel to the first and second longitudinal axes, between any of a plurality of positions at which the third magnet is disposed between the first and second magnets.