There can be little doubt that the French elevators placed in the east and
west piers to carry visitors to the first stage of the Tower had the
important secondary function of saving face. That an engineer of Eiffel's
mechanical perception would have permitted their use, unless compelled to
do so by the Exposition Commission, is unthinkable. Whatever the attitudes
of the commissioners may have been, it must be said--recalling the
Backmann system--that they did not fear innovation. The machinery
installed by the firm of Roux, Combaluzier and Lepape was novel in every
respect, but it was a product of misguided ingenuity and set no precedent.
The system, never duplicated, was conceived, born, lived a brief and not
overly creditable life, and died, entirely within the Tower.
Basis of the French system was an endless chain of short, rigid,
articulated links (fig. 35), to one point of which the car was attached.
As the chain moved, the car was raised or lowered. Recalling the European
distrust of suspended elevators, it is interesting to note that the car
was pushed up by the links below, not drawn by those above, thus the
active links were in compression. To prevent buckling of the column, the
chain was enclosed in a conduit (fig. 36). Excessive friction was
prevented by a pair of small rollers at each of the knuckle joints between
the links. The system was, in fact, a duplicate one, with a chain on
either side of the car. At the bottom of the run the chains passed around
huge sprocket wheels, 12.80 feet in diameter, with pockets on their
peripheries to engage the joints. Smaller wheels at the top guided the
chains.
If by some motive force the wheel (fig. 33) were turned counterclockwise,
the lower half of the chain would be driven upward, carrying the car with
it. Slots on the inside faces of the lower guide trunks permitted passage
of the connection between the car and chain. Lead weights on certain links
of the chains' upper or return sections counterbalanced most of the car's
dead weight.
[Illustration: Figure 28.--Plan and section of the Otis system's movable
pulley assembly, or chariot. Piston rods are at left. (Adapted from _The
Engineer_ (London), July 19, 1889, vol. 68, p. 58.)]
Two horizontal cylinders rotated the driving sprockets through a mechanism
whose effect was similar to the rope-gearing of the standard hydraulic
elevator, but which might be described as chain gearing. The cylinders
were of the pushing rather than the pulling type used in the Otis system;
that is, the pressure was introduced behind the plungers, driving them
out. To the ends of the plungers were fixed smooth-faced sheaves, over
which were looped heavy quadruple-link pitch chains, one end of each being
solidly attached to the machine base. The free ends ran under the cylinder
and made another half-wrap around small sprockets keyed to the main drive
shaft. As the plungers were forced outward, the free ends of the chain
moved in the opposite direction, at twice the velocity and linear
displacement of the plungers. The drive sprockets were thereby revolved,
driving up the car. Descent was made simply by permitting the cylinders to
exhaust, the car dropping of its own weight. The over-all gear or ratio of
the system was the multiplication due to the double purchase of the
plunger sheaves times the ratio of the chain and drive sprocket diameters:
2(12.80/1.97) or about 13:1. To drive the car 218 feet to the first
platform of the Tower the plungers traveled only about 16.5 feet.
To penetrate the inventive rationale behind this strange machine is not
difficult. Aware of the fundamental dictum of absolute safety before all
else, the Roux engineers turned logically to the safest known elevator
type--the direct plunger. This type of elevator, being well suited to low
rises, formed the main body of European practice at the time, and in this
fact lay the further attraction of a system firmly based on tradition.
Since the piers between the ground and first platform could accommodate a
straight, although inclined run, the solution might obviously have been to
use an inclined, direct plunger. The only difficulty would have been that
of drilling a 220-foot, inclined well for the cylinder. While a difficult
problem, it would not have been insurmountable. What then was the reason
for using a design vastly more complex? The only reasonable answer that
presents itself is that the designers, working in a period before the
Otis bid had been accepted, were attempting to evolve an apparatus capable
of the complete service to the second platform. The use of a rigid direct
plunger thus precluded, it became necessary to transpose the basic idea in
order to adapt it to the curvature of the Tower leg, and at the same time
retain its inherent quality of safety. Continuing the conceptual sequence,
the idea of a plunger made in some manner flexible apparently suggested
itself, becoming the heart of the Roux machines.
[Illustration: Figure 29.--Section through cabin of the Otis elevator.
Note the pivoted floor-sections. As the car traveled, these floor-sections
were leveled by the operator to compensate for the change of inclination;
however, they were soon removed because they interfered with the loading
and unloading of passengers. (From _La Nature_, May 4, 1889, vol. 17, p.
360.)]
Here then was a design exhibiting strange contrast. It was on the one hand
completely novel, devised expressly for this trying service; yet on the
other hand it was derived from and fundamentally based on a thoroughly
traditional system. If nothing else, it was safe beyond question. In
Eiffel's own words, the Roux lifts "not only were safe, but appeared
safe; a most desirable feature in lifts traveling to such heights and
carrying the general public."[12]
The system's shortcomings could hardly be more evident. Friction resulting
from the more than 320 joints in the flexible pistons, each carrying two
rollers, plus that from the pitch chains must have been immense. The noise
created by such multiplicity of parts can only be imagined. Capacity was
equivalent to that of the Otis system. About 100 people could be carried
in the double-deck cabin, some standing. The speed, however, was only 200
feet per minute, understandably low.
If it had been the initial intention of the designers to operate their
cars to the second platform, they must shortly have become aware of the
impracticability of this plan, caused by an inherent characteristic of the
apparatus. As long as the compressive force acted along the longitudinal
axis of the links, there was no lateral resultant and the only load on the
small rollers was that due to the dead weight of the link itself. However,
if a curve had been introduced in the guide channels to increase the
incline of the upper run, as done by Otis, the force on those links
traversing the bend would have been eccentric--assuming the car to be in
the upper section, above the bend. The difference between the two sections
(based upon the Otis system) was 78 deg.9' minus 54 deg.35', or 23 deg.34', the
tangent of which equals 0.436. Forty-three percent of the unbalanced
weight of the car and load would then have borne upon the, say, 12 sets of
rollers on the curve. The immense frictional load thus added to the entire
system would certainly have made it dismally inefficient, if not actually
unworkable.
In spite of Eiffel's public remarks regarding the safety of the Roux
machinery, in private he did not trouble to conceal his doubts. Otis'
representative, Hall, discussing this toward the end of Brown's previously
mentioned report, probably presented a fairly accurate picture of the
situation. His comments were based on conversations with Eiffel and
Koechlin:
Mr. Gibson, Mr. Hanning [who were other Otis employees] and myself
came to the unanimous conclusion that Mr. Eiffel had been forced to
order those other machines, from outside parties, against his own
judgment: and that he was very much in doubt as to their being a
practical success--and was, therefore, all the more anxious to put in
our machines (which he did have faith in) ... and if the others ate
up coal in proportions greatly in excess of ours, he would have it to
say ... "Gentlemen, these are my choice of elevators, those are yours
&c." There was a published interview ... in which Eiffel stated ...
that he was to meet some American gentlemen the following day, who
were to provide him with elevators--grand elevators, I think he
said....
[Illustration: Figure 30.--Upperworks and passenger platforms of the Otis
system at second level. (From _La Nature_, Aug. 10, 1889, vol. 17, p.
169.)]
The Roux and the Otis systems both drew their water supply from the same
tanks; also, each system used similar distributing valves (fig. 32)
operated from the cars. Although no reports have been found of actual
controlled tests comparing the efficiencies of the Otis and Roux systems,
a general quantitative comparison may be made from the balance figures
given for each (p. 40), where it is seen that 2,665 pounds of excess
tractive effort were allowed to overcome the friction of the Otis
machinery against 13,856 pounds for the Roux.