Magnetic brake

1. A brake comprising:

an outer stator surrounding an inner stator with an annular slot between the outer stator and the inner stator;

a coil in the inner stator adjacent to the annular slot;

a shaft extending centrally through the inner stator;

a drag plate attached to the shaft;

an impeller joined to the drag plate;

a drag ring joined to the drag plate, with the drag ring extending into the annular slot, and with the brake providing hysteresis braking, and also braking via eddy currents in the drag ring; and

a lock movable from a first position wherein the lock mechanically locks the drag ring against movement to a second position wherein the lock allows the drag ring to freely rotate.

2. The brake of claim 1 with the drag ring comprising an annular cylindrical ring section separate from the drag plate and attached perpendicularly onto the drag plate.

3. The brake of claim 1 further including vent holes passing through the inner stator adjacent and parallel to the shaft.

4. The brake of claim 1 wherein the coil comprises a coil ring positioned entirely within the circumferential slot.

5. The brake of claim 1 with the drag ring having an outer diameter DD and a wall thickness ranging from 0.02 DD to 0.08 DD.

6. The brake of claim 1 with the impeller having inner vanes extending radially outwardly from a central area of the impeller, and having outer vanes adjacent to an outer perimeter of the impeller.

7. The brake of claim 1 with the lock having a brake pad engaging the drag ring with the lock in the first position.

8. A combination hysteresis and eddy current brake comprising:

an outer stator;

an inner stator with an annular slot between the outer stator and the inner stator;

a coil associated with at least one of the inner stator and the outer stator;

a shaft extending centrally through the inner stator;

a drag plate attached at least indirectly to the shaft;

a drag ring attached to the drag plate, with the drag ring comprising an annular cylindrical ring section substantially within the annular slot, and with the drag ring having an outer diameter DD and a wall thickness ranging from 0.02 DD to 0.08 DD;

a lock including a brake pad movable via a solenoid to lock the drag ring against movement; and

a computer controller electrically linked to the coil and to the solenoid, with the computer controller controlling electrical current provided to the coil to provide braking torque that varies linearly with an input signal to the computer indicative of a desired braking torque, and with the computer controller actuating the solenoid to lock the drag ring while providing an alternating decaying current to the coil to reduce cogging.

9. The brake of claim 8 further including vent holes passing through the inner stator adjacent and parallel to the shaft.

10. A combination hysteresis and eddy current brake comprising:

an outer stator;

an inner stator with an annular slot between the outer stator and the inner stator;

a coil associated with at least one of the inner stator and the outer stator;

a shaft extending centrally through the inner stator;

a drag plate attached at least indirectly to the shaft;

a drag ring joined to the drag plate, with the drag ring extending into the annular slot, and with the brake providing hysteresis braking, and also braking via eddy currents in the drag ring;

a computer controller electrically linked to the coil and controlling electrical current provided to the coil to provide braking torque that varies linearly with an input signal to the computer indicative of a desired braking torque; and

a lock including a brake pad movable via a solenoid to lock the drag ring against movement, and with the solenoid controlled via the computer controller.

11. The brake of claim 10 with the computer providing an alternating decaying current to the coil when the solenoid is actuated.