US Patent 2,886,976 (1959): Norman L. Dean's System for Converting Rotary Motion into Unidirectional Motion

US 2,886,976 is Norman L. Dean's patent for a system that converts rotary motion into unidirectional motion. Dean filed it as an individual on 13 July 1956 (application US597805A) and it was granted on 19 May 1959; a British counterpart, GB833732A, was filed on 14 June 1957 and published on 27 April 1960. The patent describes a vibrating carriage driven by two unbalanced weights, and a timed clutch that couples the carriage to a load only during the phase of each oscillation in which it moves in the desired direction. It is a description of a mechanism and a set of legal claims. It is not a test report, and it contains no measurement of force, thrust or efficiency.

What the patent claims to achieve

The patent presents itself as a propulsion system. A prime mover supplies rotation, and what the machine is meant to deliver is one-way motion, either steady or in steps. Dean leaves open what is moved: it may be a separate load, or the body that holds the spinning parts. Elsewhere he writes that the impulses could be used to lift or propel either a load or the unit carrying the system. The patent thus mentions self-propulsion of the carrying unit as a possibility, alongside the hauling of a separate load.

The more unusual assertion concerns reaction. In the patent's account, when a system passes its motion to something outside itself, the two react on each other and the oscillation is damped. Dean asserts that his arrangement is different: the oscillator, the patent says, hands impulses to the load "without however reacting on or otherwise influencing the frequency or amplitude of the said oscillatory movement". The document states this as the principle of the invention; it offers no experiment in support of it.

The starting point: a known vibrator

Dean begins from machinery he acknowledges already existed. Two identical weights are mounted off-centre on two parallel shafts that are rigidly connected and turn at the same speed in opposite directions. Along the line joining the shafts, the forces from the two weights oppose and cancel; at right angles to that line they add. The frame carrying the shafts therefore shakes back and forth along a single line about a central position. The patent says devices of this kind had been built for testing and for producing regular vibration, and it also describes an equivalent with a single eccentric weight confined by a linear guide.

The Google Patents listing for the patent records two earlier citations: Aubrey C. Nowlin's US2350248A, a device for obtaining directional force from rotary motion (published 1944), and General Motors' US2700542A, a vibration driven actuator (published 1955).

What Dean adds: coupling and shifting

The invention proper is a pair of timed operations laid over this oscillator.

• Coupling. During the part of the cycle in which the resultant force points the desired way, a clutch joins the oscillating unit to the load. On the back swing the clutch lets go. The clutch may be mechanical, with eccentric jaws gripping a tape, cord or cable, or electromagnetic, acting on a steel tape directly. The mechanical version is said to suit heavier loads.
• Shifting. After the back swing, solenoids push the unit toward the load, to a fixed reference position, before the clutch closes again. The patent times this for the moment when the resultant of the forces is approximately zero, so that the shift meets the least resistance. It argues that the resistance then excludes the inertia of the weight and consists only of the shaft and frame.

That last argument drives a design rule: the weights should make up as much of the carriage's total weight as construction allows, in steel or heavy alloy, with the carriage and shafts in light metal, light alloy or plastic. The weights are to spin at as high a speed as possible, though no speed, mass or dimension is given.

Timing is handled electrically. Cams or commutators on the shafts close circuits according to the angular position of the weights, and slide contacts between the moving and fixed frames add a second condition, so that a solenoid or clutch magnet is energised only when both the weights and the carriage are in the right place. The clutch can close only after the shift. Dean stresses that these contacts must be finely adjustable and precisely timed for the device to run smoothly, and that the spring tension needs equally fine adjustment.

The illustrated machine

The embodiment in Figures 8 to 10 is a carriage with side plates running on balls or rollers along tracks in a fixed outer frame, and held between adjustable springs that return it toward a central reference position marked RR. The two weighted shafts are geared together so they counter-rotate. The motor may sit on the carriage or on the fixed frame; in the latter case it drives through a universal joint, a splined or telescopic intermediate shaft, and a torsion spring coupling that absorbs the momentary slowing of the shafts when the solenoids shift the carriage.

The carriage advances a steel tape to which the load is attached. While the clutch is open, a spring-loaded clamp working against a fixed jaw stops the tape sliding back. The patent adds that the system may instead be advanced along a fixed tape, that the orientation of the frame and carriage does not matter, and Figure 11 shows six units working on a single tape.

What the document does and does not show

The patent was granted, but a grant does not show that the device works as asserted. Nothing in this text reports a built machine being weighed, timed or measured, and no figure for delivered force appears anywhere in it.

Several features of the described machine bear on one question a reader is likely to ask: does a sealed unit of this kind generate net thrust? The illustrated device is not isolated: its carriage rides on tracks in a fixed frame, is tethered to that frame by springs, is pushed by solenoids shown mounted on the frame, and holds its load with a clamp against a fixed jaw. The patent itself says the oscillating system is "cyclically shifted by external forces". A tape hauled along past a stationary frame is a different thing from a sealed box that moves itself, and the patent describes only the former in detail while asserting the latter as a possibility. Whether the claimed absence of reaction on the oscillator holds is exactly what the document leaves unestablished.

Afterlife in the patent record

The patent's status is listed as expired, with an anticipated expiration of 19 May 1976. It has since been cited by more than two dozen later patents. Many pursue the same goal, among them a gyroscopic inertial space drive (US3203644A, 1965), a unidirectional force generator (US4261212A, 1981) and several simply titled Propulsion system. Others are mundane relatives of the underlying vibrator: compaction rollers, vibrating screens, a concrete press table and Tomy Kogyo's moving toys (US4291490A, 1981). One, US10482790B1 (2019), is a teaching aid for explaining the principles of an impulse driver. The classification of Dean's patent places it among vibration generators with unbalanced masses on counter-rotating shafts and among mechanisms converting rotary into intermittent unidirectional motion.

Further reading

A 2006 NASA technical memorandum by Marc G. Millis and Nicholas E. Thomas names this patent as one of the most famous "oscillation thrusters" and attributes the apparent thrust of such machines to the difference between static and dynamic friction with the ground; it also proposes a level-pendulum test for any claim of net thrust. See Responding to Mechanical Antigravity (2006): Millis and Thomas on Why Oscillation Thrusters Like the Dean Drive Only Appear to Produce Thrust.

For the private demonstrations, the Astounding/Analog and Popular Mechanics coverage, Dean's second patent (3,182,517) and the later assessments, see The Dean Drive: Norman L. Dean's Reactionless-Drive Claim, Its Demonstrations, Its Publicity and How It Was Later Judged.

G. Harry Stine, who watched Dean run a machine in 1960, wrote in Analog in 1976 that this patent will not tell a reader much about how to build a Dean Drive, and described test rigs built around the same counter-rotating-weight oscillator; see Detesters, Phasers and Dean Drives (1976): G. Harry Stine's Witness Account of the Dean Drive and the Huyck Corporation Tests.