Around the casing and bolted securely to it is a channel frame, on which is placed two 36 by 31⁄2 inch solid rubber tires. This construction makes the over-all width of the tire about 8 inches, a width that is very advantageous for travelling over muddy or loose sand roads. The wheel has two circular hand holes for oiling and inspection. The completed wheel is water-tight, as continued immersion has shown. The truck has been called upon a number of times to ford streams in which the wheels were submerged to axle.

Fig. 3. Couple-Gear Wheel with Tire and Band Removed, Showing Rela tive Positions of Driving Pinions and Circular Rack

The frame consists of 5-inch channel irons on both sides, connected in the rear by 5-inch channel cross bar and in front by a semi-elliptical formed channel. At a number of points along the frame channel, iron and oak braces are inserted.

The axles are of phosphor-bronze and are of the rigid type, the wheels being held to the axles by knuckles similar to the type used in automobile front axle construction.

The frame is connected to the axles through semi-elliptical

springs arranged to give a three-point suspension. The rear springs are longitudinal, and have at their middle points cushion and recoil coil springs. It has been found in heavy work that it is not the downward, but the upward, movement that breaks a spring. The addition of recoil springs on the car has added greatly to its easy riding qualities; in fact, it is almost as comfortable a riding vehicle as a heavy touring car. The front suspension consists of two semi-elliptical springs placed back to back and securely fastened by a king-bolt. This construction has proven very satisfactory and is very desirable for cross-country travelling.

GENERATING SET

The gasoline-engine generating set consists of a semi-automobile type, 5 cylinder, 4 cycle, 5 by 6 inch Dock, enclosed type gasoline engine specially designed for this service, direct-connected to a 15kilowatt, Sprague, 6-pole, 85-volt, inter-pole, direct-current, compound generator.

The engine is of a type that may be placed mid-way between those used for gasoline automobile service and those used for stationary service. The automobile type of engine will not satisfactorily stand up to generating service: first, because the parts are not made heavy enough and, second, because the design of cooling water-jackets are not made liberal enough for carrying a continuous load and constant speed. The Dock engine is a compromise between the advantages and disadvantages of a 4 and 6-cylinder type, and for this constant speed work has given excellent service. The engine is fitted with dual system of ignition, consisting of a single coil, battery and high-tension distributor, and an Eiseman low-tension magneto, non-vibrating coil, and the same high-tension distributor. The magneto is used exclusively for running; the battery and coil being used only in cases of emergency and for starting. The engine was originally equipped with an air starting device, but it was later found to be unnecessary, as the cranking method was simple and reliable.

The engine is equipped with a fly-ball throttling governor, McCord force feed lubricator, and Stromberg float-feed carburetor. Gasoline is delivered to the carburetor from a sight reservoir which gets its gasoline from the lower tank through a plunger pump. Gasoline may also be fed from the upper tank direct to the carburetor. The car, as shown in Fig. 2, has a gasoline tank capacity of 87 gallons.

The performance of the generating set is shown by the characteristic curves exhibited in Fig. 5. These curves are self-explanatory.

The generator is of a special light-weight design of the interpole type. It is direct-connected to the engine by a flange coupling and is supported on a cast aluminum sub-base integral with the engine base. The inter-pole construction of the generator has made it possible to carry for short periods as high as 75 per cent overload without excessive sparking or heating. This is particularly a good point, since a car of this type will be frequently called upon to pull itself or neighbors out of mud holes or up steep grades.

Fig. 4. "Couple-Gear Wheel with Side of Wheel and Front of Motor Casing Removed, Showing Arrangement of Armature, Poles, and Bearings

The engine is water cooled, the water in turn being cooled in a surface radiator of the Mayo type. This radiator is cooled by air drawn through it from the front of the car by a suction fan which is driven from the generator end of the shaft by a Morse silent chain. It is of such a capacity that the generating set could operate continuously at 25 per cent overload capacity with an air temperature of 100° F. without overheating the jacket water.

CONTROL

The speed of the car is controlled by an eight-point series-parallel, four motor, street car type, drum controller. The current is supplied at constant voltage at from 80 to 110 volts. The first

point on the controller throws two motors in parallel and in series with the other two motors, which are also in parallel; the series parallel combination being in series with the starting resistance. The second and third points reduce the starting resistance and the fourth point cuts out all resistance, but maintains the series-parallel connection. This is the first running point. The fifth point throws all motors in parallel and the combination in series with the starting resistance. The sixth point cuts out a portion of the starting resistance, and the seventh all of it, leaving all four motors in parallel on the full bus-bar voltage. This is the second running point. The eighth and high speed point throws a shunt around the motor fields, thereby giving a greater speed. By this combination any speeds from 3 to 10 miles per hour ahead or reverse can be maintained, a control that can not be obtained efficiently with any other system. This control makes it possible to utilize the available power of the plant in the most economical and desirable manner. It also makes it possible to follow a column of mixed troops or of any one kind of troops.

STEERING AND BRAKES

The car is equipped with four-wheel steer as well as drive. The steering wheel and vertical post are connected to the steering quadrants through a horizontal tumbling rod and worm gearing in such a manner that when the front wheels are deflected to the right the rear wheels are deflected at a corresponding angle to the left. The advantages of this arrangement are that, first, the car can be handled better in tight places and, second, on muddy roads the wheels always track and, therefore, the rear wheels do not have to break a second track when the car travels around curves. The steering mechanism is also equipped with a device, so that by manipulating a small lever on the steering post the rear wheels can be clamped in a straight-ahead position and the two front wheels alone steered. The advantage of this arrangement is that at high speed the car can be more easily and safely operated with the two-wheel steer.

The brakes of the car are both mechanical and electrical. There are external contracting brakes on all four wheels, arranged in pairs; the rear brakes being connected to the right pedal and the front brakes to the left. The electrical braking is accomplished by using the reversing drum of the main controller as an electrical brake controller. In this system the wheel motors are used as gen

erators, they being connected by the reversing or braking drum to resistances. As soon as the motors, as series generators, are connected by this drum to the resistances they become loaded and tend to stop. The electrical brake is used only in cases of emergency or on descending long grades. The latter use is very desirable, as it

Fig. 5. Test of Dock Gasoline D. C. Generating Set. Five cylinders-5-inch diameter, 6-inch stroke. Sprague Interpolar Generator, 85 volts, 15 kilowatts.

saves the foot or mechanical brakes from rapidly wearing away their fiber linings.

SWITCHBOARD

The dash of the car contains a complete direct-current switchboard for the entire plant. It consists of an automobile volt

Pints

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2

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