THE MANCHESTER MOTOR.
Those readers who have made the motors already described, are no doubt anxious to proceed with the construction of some models which bear a greater resemblance to the large motors commonly employed to furnish power.
Figure 29 shows a motor of the "Manchester" type.
The Field of this machine is made from a strip of heavy sheet tin, one-half inch wide and about six inches long, bent to shape and joined in the center of the bottom pole piece, just above the pedestal. It is best to cut the strip a little long and then reduce it to the exact length required after the bending operations have been finished. The illustration in Figure 30 shows the details and dimensions of the field.
The field should be bent into shape with the aid of a pair of pliers and a wooden form, in the same manner employed in making the motors already described.
FIG. 28.—The Manchester Motor.
The field frame is supported by a "pedestal." The pedestal is formed by another strip, one-half inch wide, soldered to the field at right angles, underneath the joint in the lower pole piece.
The pedestal should be firmly soldered to the field, care being taken to see that the solder runs well into the joints. Then bend the ends of the pedestal down to form two "feet" as shown in the illustration. The feet should be bent so as to bring the center of the armature tunnel five-eighths of an inch above the base.
Two small holes should be bored in the pedestal, at each side, so that the motor can be screwed fast to a wooden base.
FIG. 30.—Details of the Field Frame.
Winding the Field—It will be necessary to proceed with the winding of this motor in a slightly different manner from that followed in making the other motors. The wire cannot be wound on as easily as before and it will be necessary to wind the required length of wire onto a small spool or bobbin, which can be passed through the field. Double cotton-covered wire is the best for the purpose. Either No. 25 or No. 26 B. & S. Gauge may be used. A strip of paper should be wrapped around the field frame at all points where the wire is liable to touch, so as to guard the insulation against possible abrasion.
Figure 32 shows the method which should be followed in winding the coils. Both parts of the winding should be started at the bottom of the field and wound in the direction indicated. "B" and "D" are the starting ends Wind on three layers of wire in each coil. The terminals, "B" and "C," should be connected together after the winding is finished.
The Armature—The method of making the armature is exactly the same as that which has already been described. Three strips of tin, one-half inch wide and one and one-half inches long are required. They are purposely made slightly longer than is actually necessary and are cut to length after the finish of the bending operations.
FIG. 31.—Details of the Field Pedestal.
Mark a line carefully across the center of each of the three strips and then bend them into the shape shown in Figure 20, making certain to keep the shape symmetrical so that all three, pieces are exactly alike. The bend in the center of each strip should fit nicely over the shaft. This result is most easily reached by bending the strips over a knitting-needle and then bending them back the required amount.
FIG. 32.—Showing how the Field Coils are Wound.
The Shaft is a piece of knitting-needle one and seven-eighths of an inch long. Assemble the three strips on the shaft as shown in Figure 21 and bind them temporarily together with a piece of iron wire. Then solder the edges together and remove the wire.
The Commutator Core is formed of a strip of paper, three-eighths of an inch wide and about five inches long, wrapped around the shaft until the diameter of the small cylinder thus formed is three-sixteenths of an inch. The paper strip should be given a coat of shellac on one side and allowed to dry until it becomes sticky before it is wrapped around the shaft. The sticky shellac should be sufficient to hold the paper tightly in position when dry and to form a hard, firm core when dry.
The Winding of the Armature is not difficult. The size of the wire used should be No. 25 or No. 26 B. & S. Gauge, double cotton-covered.
Wrap a strip of paper around each section of the armature so that the wire will be protected from any sharp edges on the tin which might cut through the insulation.
Wind four layers of wire on each section of the armature. Each section should be wound in the same direction as the others. The terminals of the wires should be scraped clean and connected together in the following manner: Connect the outside end of one section to the inside end of the next section. We will presume that the three sections of the armature are lettered "A", "B" and "C." Connect the outside end of "A" to the inside of "B"; the outside of "B" to the inside end of "C" and the outside end of "G" to the inside of "A."
The portion of the wires forming the connections between the three armature coils are used to form the three sections of the commutator.
Bend the wires so that they will fit closely to the paper core and bind them tightly into position with silk thread.
Two Bearings are required to support the armature. They are cut out of sheet iron or brass and are shown in detail in Figure 12. Extra care should be exercised in making the bearings to insure their accuracy so that the armature will be in the proper position when the motor is assembled and run freely.
Two small washers or wire rings, to serve as collars and keep the armature in the center of the field, should be soldered to the shaft as shown in Figure 22.
The Base is a square block of wood, two and one-half inches wide, two and one-half inches long and three-eighths of an inch thick.
The completed Manchester motor is shown in Figure 29. The brushes are made by flattening the ends of two pieces of copper wire. Each brush is fastened under a small clamp made from a strip of tin held down at each end by a small round-headed wood screw.
Be sure that the armature is exactly in the center of the field, does not scrape at any point and turns perfectly freely.
The armature and the field windings should be connected in series. The terminals of the field marked "B" in Figure 32 should be connected to the brush clamp marked "C" in Figure 29. The terminal of the field marked "C" in Figure 32 forms one terminal of the motor. The other is the brush clamp "A."
Oil the bearings of the motor, adjust the brushes and it will be ready to run.