The first elevator motors powered building-wide belt driving shafts in manufacturing facilities, so they were external to the elevators. But space and manufacturing costs could be saved by integrating the motor directly into the elevator assembly. That was accomplished before 1890, and is how it remains today.
Before the end of the nineteenth century and continuing to the present, electric elevators improved, with new designs becoming safer and more efficient. A key figure in this development was Frank Sprague, shown in Figure 1-5.
Electric motors and their applications in human transportation were Frank Sprague’s life. After graduating from the U.S. Naval Academy and a short stint on ship and in Europe, the young electrical engineer joined Edison’s large assembly of electricians, mechanics, and glassblowers in the lab at Menlo Park. While Edison was focused on producing a practical electric light bulb, Sprague wanted to develop a DC motor that would maintain RPM under varying loads. Edison was temperamental, but went along with this idea.
FIGURE 1-5 Frank Sprague (1857–1934) (Wikipedia)
Prior to 1880, electric motors were repurposed electric generators, then known as dynamos, which had preceded them. It had been found that voltage applied to what had been the generators’ output terminals would cause them to turn. These devices would actually run and could be configured to perform work, but they left a lot to be desired.
Sprague had some big ideas. He envisioned a DC motor that could run a loom, hoist, pump, blower, or machine tool. His highest ambition, eventually realized, was to build powerful motors that were reliable and capable of powering railroads, replacing the inefficient, smoky, and dangerous steam engines of the day.
Dynamos repurposed as motors bogged down under heavy load, and while this didn’t make much difference in some applications, in others these primitive devices were not suitable. A skilled mechanic was needed during running hours to advance or retard the brushes and adjust field strength for various loads and RPMs.
Sprague, at this juncture and throughout his life, demonstrated that Edison wasn’t the only electrical and mechanical genius. While Sprague has had less impact than Edison in the popular imagination, in many ways he was more advanced and insightful. Sprague built an electrical motor that maintained constant speed under varying load. Rather than the steam engine’s mechanical governor, Sprague’s electrical motor incorporated a reverse winding that automatically varied field strength in response to speed and loading. He solved the problem of brush position not by moving them physically, but by rotating the magnetic field to achieve the required alignment.
Since Sprague was working for Edison, the improved motor design at this point belonged to Edison. Sprague evidently saw the writing on the wall, and shortly thereafter tendered his resignation.
While Edison continued to refine his incandescent light bulbs and DC power generation and distribution system, Sprague, after eleven months working in Edison’s large organization, formed the Sprague Electric Railway and Motor Company. His lifelong project was to move rail traffic by means of electric motors. In this he was very successful and was renowned among electricians and transportation workers as “the father of electric traction.” He came to define these words to include vertical as well as horizontal traction. His elevator work was a relatively brief interlude, but its impact was enormous. After completing some difficult early streetcar and railway projects, he turned his attention in 1889 to elevator design and construction.
Sprague, together with his old friend Ed Johnson and elevator manufacturer Charles Pratt, rented a factory building and in 1892 formed Sprague Electric Elevator Company. Ed Johnson was the legal and financial specialist. Sprague provided electrical expertise, and Pratt was the mechanical engineer. Together they planned to offer two very different types of elevators. For low-rise buildings, a conventional drum-type elevator would be reconfigured with a reversible, adjustable-speed electric motor replacing the steam engine.
For high-rise applications, a faster machine would consist of a large, threaded-steel shaft placed horizontally and powered through a gearbox by an electric motor. A large nut would move along the turning shaft, driving a cable pulley. The contraption actually worked, and in fact dominated the industry until shortly before the turn of the century.
After constructing a small prototype in their new Manhattan facility, the firm secured a contract to install a similar elevator in the Grand Hotel in New York City.
There were problems in this installation. The control system, which had been satisfactory in Sprague’s electric trolleys, did not provide the smooth performance required in an elevator.
Sprague’s electrical expertise was severely challenged. First, he built an improved resistance network, known as the grid, for the controller. This smoothed out the elevator motion, but the resistance network and controller mechanism heated and contacts had to be replaced.
The elevator was put back in operation, but after a few days at an upper floor the ascending car suddenly dropped, its speed doubling, coming to a stop after striking the bumpers at the bottom level.
Fortunately, there were no injuries. The cause was determined to be a defective motor that ran the reversing lever in the controller. The sudden reversal damaged the safeties, permitting the car to drop.
Soon redesigned safeties and controls were in place and the elevator resumed normal operation. This did not solve the network problem. Eventually, the firm built and installed a new controller with heavier contacts, but the problem persisted. Sprague favored a cast iron grid, which turned out to work on a long-term basis. The Grand Hotel signed off on the project and Sprague Electric Elevator Company moved on to another project, the Postal Telegraph Building. This was to be located close by on Broadway and be far bigger and faster than the Grand Hotel installation. There would be four local and two express elevators, rising 14 stories above street level.
The immense screw and traveling nut mechanisms resulted in heavy loading and increased friction, which Sprague intended to mitigate by incorporating captive steel balls within the nuts.
After mishaps and delays, the Postal Telegraph Building installation performed flawlessly in tests and was placed in operation. It was a prestigious project, and the Postal Telegraph Company Building Committee was well satisfied. But unfortunately, the country was enduring a severe financial depression. New building had halted, and orders were not coming in. Sprague, never one to let up, had some ideas for improving elevator safety and efficiency, and the business slowdown allowed time to work on them. One innovation was the self-centering “dead man’s control,” which stopped the car if for any reason the control was released by the operator. Another innovation was an automatic elevator that incorporated door interlocks and floor alignment. Sprague stuck with the screw and nut design, rather than going with an improved traction drive, which together with his electric motor became the wave of the future. The business climate improved and by 1895 new orders soared and the company moved to a larger facility across the Hudson River, in New Jersey.
In 1898, Sprague decided to return to his first love, railroad electrification. He sold the elevator business to Otis for $1,000,000, retaining royalty rights to two thirds of foreign business and rights to lease back plant and equipment for five years. With that transaction Sprague became much less of a presence in the elevator world, in which Otis was now the most prominent player.
Elisha Graves Otis (1811–1861), a skilled builder and mechanic, in 1850 found his way to Albany, New York, where he was employed to manage a bedstead factory. Relocating