SIMPLEX MOTOR WITH THREE-POLE ARMATURE.
The form of "Simplex" motor which has just been described has only one drawback which prevents it from being a first class motor in every respect, namely, the armature has only two poles and the motor is therefore not self-starting, but must be given a twist with the fingers in order to start it rotating. A Two-pole armature is the easiest for the young experimenter to make and that is the reason that it has been described first.
All large power motors are provided with armatures having a large number of poles so as to be self-starting and to give as steady a pull as possible.
The Armature—The method of making a three-pole armature is practically the same as that of making one having only two poles. Three strips of tin, one-half an inch by one and one-half inches are necessary. They are purposely made a little longer than is actually required in order to form the armature and are cut to length after the finish of the bending operations.
FIG. 20.—Details of the Three-pole Armature.
Mark a line carefully across the center of each strip. Then bend them into the shape shown in Figure 20, taking care to keep the shape symmetrical so that all three pieces are exactly alike. The bend in the center which must fit over the shaft is most easily made by bending the strips over a knitting-needle and then bending them back the required amount.
The Shaft is formed by a piece of knitting-needle, one and seven-eighths of an inch long. Assemble the three pieces, forming the armature, on the shaft as shown in Figure 21. Bind them temporarily together with a piece of iron wire and then solder them along the edges. The iron wire should be removed after they are soldered.
The Commutator Core is formed by cutting a strip of paper, three-eighths of an inch wide and about five inches long. It should be given a coat of shellac on one side and allowed to dry until it becomes sticky.
FIG. 21.—The Three-pole Armature assembled on the shaft.
The strip is then wrapped around the shaft until its diameter is three-sixteenths of an inch. The sticky shellac should be sufficient to hold the paper tightly in position when dry and to form a hard, firm core.
The illustration in Figure 22 shows the position of the core on the shaft in relation to the rest of the armature.
The Winding of the Armature may seem somewhat more difficult at first than was the case with the two-pole armature, but it is really very easy. The wire used for this purpose should be No. 25 or No. 26 B. & S. Gauge, double cotton-covered. Single cotton-covered wire for this purpose is liable to give trouble on account of short circuits.
In order to wind the armature, cut three pieces of wire about three and one-half feet long. Wrap a strip of paper around each section of the armature so that the sharp edges of the tin will not cut through the insulation on the wire and then wind four layers of wire on each section of the armature.
FIG. 22.—Showing the Armature and Shaft with the Commutator Core in position.
Each section should be wound in the same direction as the others. The ends of the wires should be scraped free from insulation and connected together as follows: 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 of "C" to the inside of "A."
Those portions of the wire forming the connections between the three sections, are used to form the commutator segments, in the same manner as the ends of the wires in the case of the two-pole armature, only in this instance there are three sections to the armature.
FIG. 23.—Diagram showing how the coils are connected together so as to form a continuous winding.
Bend the wires so that they will fit closely to the paper core and bind them tightly into position with some silk thread. A section of the commutator should come opposite the space between each section of the armature.
The Field Magnet is exactly like that used in making the Simplex motor with the two-pole armature. It is made by first cutting out a strip of tin five-eighths of an inch wide by five inches long and then bending it into the shape shown in Figures 10 and 11. The easiest way of doing this with reasonable accuracy is to cut out a piece of wood for a form and then bend the tin over the form.
Two small holes should be bored in the feet of the field magnet so as to enable the field to be fastened to the base.
The field is wound with the same size of wire used on the armature. The winding is started by looping a small piece of tape or cord over the frame at the point indicated by "A" in Figure 15. The next two turns are then wound over the ends of the loop so as to hold them down. Wind on three layers of wire on one side and then run the wire across to the other side and wind on three layers there. The third layer of wire in the second coil should end at B. It should be fastened in position by a loop of string so that it will not unwind.
This method divides the field winding into two parts, both of which are connected together. The outside layer of the first coil is connected to the inside layer of the second coil. The two coils really form one continuous winding divided into two parts. The illustration in Figure 23 should make this clear. After the winding is finished, give it a coat of shellac.
The Bearings are shown in detail in Figure 12. They are easily made. Care should be taken to make the bearings very accurate so that the armature will be in the proper position when the motor is assembled.
Two small washers, serving as collars to bear against the inside of the bearings and keep the armature in the field should be soldered to the shaft as shown in Figure 13.
The Base is cut from any ordinary piece of wood and should be in the form of a rectangular block about two and one-half inches by one and seven-eighths inches wide, and one-half inch thick.
The completed motor is shown in Figure 24. Be sure that the armature does not scrape against the field at any point but clears it by about one-sixteenth of an inch all around. The brushes are fastened under a small clamp made from a strip of tin held down at each end by a small wood screw. The brushes are made by flattening the end of a piece of copper wire with a few light hammer blows. The brushes can be best adjusted under actual working conditions when the current is passing through the motor.
One end of the field winding is connected to the brush marked "C," in Figure 24. The other brush, "A" and the other end of the field winding, "B," form the terminals to which the battery is connected. This forms what is known as a series connected motor, because the armature and the field are in series and the current must pass from one to the other.
FIG. 24.—The completed Three-pole Motor.
After you have finished assembling the motor, put a drop of oil on the bearings, make certain that the brushes are properly adjusted, connect the battery, and your motor is ready to run. One or two dry cells should furnish sufficient current to run the motor at high speed.