MAKING A SMALL ELECTRIC AUTOMOBILE (Apr, 1924)
MAKING A SMALL ELECTRIC AUTOMOBILE
By E.B. Stack.
THE electric automobile described in this article is not merely a toy, but a real electric car. It was designed and made for children, but will carry a load of four hundred pounds with ease. Every part, while made as light as possible, is strong enough to stand any amount of rough usage. It is ideal for the youngster who is past the coaster-wagon stage, but not yet old enough to be allowed to run the “flivver.”
The body is built of poplar, with a streamline hood, and is supported by a steel chassis. The angles for the chassis were obtained from a discarded iron bed, and the bumpers were made of the same material. Steel disk wheels, about 10 in. in diameter are used, fitted with 1-in. rubber tires; these can be obtained from many supply houses, or taken from a coaster wagon. The two front wheels are ball-bearing, mounted in the same manner as in an automobile, as shown in Figs. 1 and 3, and in the detail drawings. The rear wheels are fastened tightly to the 5/8-in. rear axle by means of pins. The axle runs in three bearings, each bearing being made by bolting two 3/4 by 3/4 by 3-in. pieces of steel together, and drilling the bearing hole across the joint, thus leaving half of the bearing in each piece. The bearing bolts pass through a poplar crosspiece bolted to the chassis of the car. Tin covers are made and screwed over each of the bearings; these are packed with oil-soaked waste, to lubricate the bearings. A small pulley, about 4 in. in diameter, is setscrewed to the center of the shaft, to act as a brake drum, and a thin piece of sheet steel, faced with regular brake lining, used as a brake. The method of mounting this and the connections to the brake pedal are clearly shown in the detail drawing.
Four bicycle sprockets and two chains form the transmission used to drive the car. Two of the sprockets are about 8 in. in diameter, and two 2-l/2 in. One small and one large sprocket are pressed on a 5/8-in. steel shaft 6 in. long. The sprockets are made to fit the shaft by using bushings, which are turned in a lathe, and screwed or riveted to the sprockets; the sprockets are then fastened to the shaft by drilling through bushings and shaft and driving in steel pins. The large sprocket on the rear axle is fastened in the same way; it is best to ream the holes with a taper reamer and drive in taper pins. A similar method of fastening is used for the rear wheels.
The steering mechanism is similar to that of the regular automobile, and a Ford steering wheel and rod are used. The drag link may be 3/8 or 1/2-in. steel rod, with the ends flattened and drilled for the bolts. The manner of connecting the links to the pivoted wheels, and the method of pivoting the wheels are clearly shown.
The hood of the car may be made of galvanized iron, or heavy stovepipe iron. The latter is perhaps preferable, as it holds the paint better. The two 6-volt batteries that supply the current are carried under the hood; they are connected in parallel, thus increasing the capacity while keeping the voltage down to the 6 volts necessary for the motor.
The motor is a standard 6-volt automobile-starting motor, and the remaining 2-1/2 in. sprocket is pressed on the end of the shaft and pinned. The motor is hung to the underside of the car by means of a heavy flat-steel strap.
The oil switch is made from a piece of slate 1/2 to 3/4- thick, by 2 in. wide and 4 in. long; on this is mounted one dead, or “off” contact, and one that is connected to the motor.
These are made of 1/2-in. square copper bar, 1 in. long, and are fastened to the slate panel 1/4 in. apart. An iron rod, 1/2 in. in diameter, and 5 in. long, with a foot button on its upper end, passes through the floorboards of the car, and on the lower end of this rod is a copper contact. A compression spring is slipped on the rod between the foot button and the floorboard, to keep the rod on the off contact. When the rod is pressed down, it makes contact with the motor connection, and the car starts. Over this switch is placed a 2 by 3 by 4-1/2-in. galvanized-iron box, with soldered seams. This is kept nearly full of transformer oil, to prevent sparking or arcking at the contacts. About 7 ft. of No. 2 starter cable is needed to wire the car, the connections being as shown in Fig. 3. A knife switch is mounted under the car, as shown, to break the circuit when the car is not in use.
The storage batteries may be recharged from any convenient 6-volt direct-current source, but a more convenient method is to mount a small rectifier under the seat of the car, and connect it permanently to the battery. A receptacle is mounted flush on the dash, and during charging hours connection is made to this plug from a 110-volt a. c. supply. A small ammeter, also mounted on the dash, should be connected in the circuit to show the current flowing to the batteries, to prevent reversal. The car weighs about 150 lb. complete, and has a speed of about 10 miles per hour under full current. With two 80-amp. hour batteries, fully charged, it will run about 5 miles. The car will climb steep grades with two or three passengers.