Direct-Current Motors: Automatic Armature Winding Pioneering Theory and Practice

Background

In the 1930s, the electrical manufacturing industry began to realize and attempt to meet the demand for small electrical motors.

In the low-voltage range, these included 6- or 12-V dc motors for automotive fans, windshield wipers, window operators, etc.; and 15- to 30-V ac motors for toy trains, erector sets, and other toys. In the household voltage range, these included motors for sweepers, mixers, and hand tools.

These motors were of a two-pole, series-connected arrangement, having a slotted armature, with coils wound into nearly diametrically spaced slots, with start and finish wires connected to adjacent bars on a commutator. Large production rooms were filled with workers using simple tools and equipment to insulate the slots, place the coils therein, wedge them in place, connect them to the commutator, and so on.

The advent of World War II nearly halted the production of these motors for peacetime uses, requiring production of motors to the more exacting requirements of the armed services for navigation and munitions control devices. More handwork was required, and mechanized apparatus was more restricted in meeting the extremely rigid specifications set by the services.

Following the end of the war, peacetime requirements surged. At the same time, labor tended to hold back production rates. It became necessary for the machines to pace the operators, whereas the operators could previously be depended on to pace the production from simple machines and fixtures.

Semiautomatic Winding Methods

For years, the armature had been held in a fixture fitted with guide wings, which was rotated (end over end) for the desired number of turns within a coil, stopped, and positioned by the operator. A lead loop was pulled and laid on a hook or under a clip. The armature was indexed in the fixture to the new coil location, and the process was repeated.

Technique and kinds of lead loops as well as sequence of indexing varied between different applications and according to the ingenuity of the manufacturer's designer.

Certain patterns became geographically popular.

Then the method of holding the armature stationary and spinning the wire in with a flier became popular. The operator could now index more simply, and could hold the lead loop with a finger while starting the next coil.

All these methods involved hand operations which could not efficiently be mechanized to produce the full variety of armature patterns and lead shapes to which each manufacturer had become accustomed.

Automating the Wind Cycle

It became necessary to standardize the armature production industry with mechanisms in mind, rather than involving the human element. Only then could automatic machines gain acceptance.

As customers became interested in automatic equipment, their specific armature patterns were analyzed, and new patterns substituted, permitting mechanization. The writer recalls spending long tedious hours in conference with engineering groups in each customer instance, illustrating the equivalency of our recommendations to their favorite customary method. Eventually, one by one, they became sufficiently convinced to ask for test samples for actual proof.

During the past quarter century the appropriateness of the automatic equivalent winding patterns, along with the economic pressure for automation, has brought an end to the era of hand-wound armatures. Today's designers following industry standard armature practices don’t even realize that such practices were developed by Globe in order that armature production could be automated.

Armature Analysis Method

The following theory is recorded in order that this tried and proven method of armature analysis can be relied upon, with confidence, in the application of further improvement methods.

In general, the small series-connected motor, frequently called the universal motor, consists of a two-pole field surrounding the armature, as shown in FGR. 110.

FGR. 110 Universal motor field winding.

The field yoke may be circular, as illustrated, with coils on each pole; or it may extend from pole to pole only on one side of the armature, as in FGR. 111, in which case there is usually only one field coil on the leg of the yoke. In many cases, permanent-magnet fields are used, wherein no field coils are required.

The armature may have 12 slots and a 12-bar commutator wherein there will be 1 coil per slot (2 coil sides per slot).

There may be from 8 to 12 slots; and in rare instances numbers beyond this range.

Also, there may be two coils per slot (four coil sides in each slot) in which case there are twice as many commutator bars as slots. In rare cases, there may be three coils per slot.

The brushes may be located in line with the center of the poles, or shifted in angularity there from at the will of the designer, usually for convenience of space, access, or other reasons. In such cases the coil leads are similarly extended.

FGR. 111 Single-coil-type universal motor field winding.

FGR. 112 Armature winding showing brushes located in center pole.

FGR. 113 Armature winding showing brushes located offset from center pole.

The single-coil 12-slot armature with in-line brushes has been selected for simplicity in introducing this analysis. Also, the coils are shown to be wound as from a single wire continuing from coil to coil in sequence, as from a single-flier winder. The result is a single-lap appearance to the finished armature, with small start coils, medium single-overlap coils, and large double-overlap final coils, producing inherent electrical and mechanical unbalance in the armature. This is in contrast to double-flier-wound armatures which show a double-lap finish with similar equal and opposite coils, resulting in good balance.

In the end views, such as in FGR. 114, looking at the commutator end, the outer two rings of dots represent eventual coil sides, while the inner ring of dots represents the commutator bars. Brushes are indicated inside the commutator ring for clarity, whereas they normally extend to the outside.

The side views, as in FGR. 114, illustrate the armature as though it were unrolled and laid out flat. This is usually the only view used in analyzing the winding pattern.

FGR. 114 Armature lap winding, first coil retrogresses: (a) end view, and (b) side view.

As the armature rotates, the brushes, in contacting the commutator bars, each will touch two adjacent bars. This shorts out the coil attached there, and that coil is said to be under commutation. In other words, prior to becoming shorted the current flowed in one direction, but after clearing from the short, the current will flow in the opposite direction through the coil. This shorting must occur while the coil sides are not under the poles. Otherwise the induced voltage in the shorted coil would over heat the coil, also causing severe sparking and burning of the brushes and bars.

Note in FGR. 114, that the commutating coils are indicated by a small circle on the coil sides. Also, the direction of current flow in the active coils is indicated by the arrowhead (from + toward -), FGR. 116.

The direction the motor would run is indicated by the circular arrow in the end view when full conditions are disclosed.

FGR. 115 Armature lap winding, first coil progresses: (a) end view, and (b) side view.

Winding Specifications

Normally, a 12-slot armature is wound to a 1-to-6 pitch (one slot short of diametric).

In the armature selected for analysis, shown in Ills. 4.114 to 4.125, the direction of wind is away from the commutator in slot 1, towards slot 6. In a double-flier winder this is left flier top coming (LFTC).

The retrogressive wind ( FGR. 114) connects the finish wire to the second bar to the right (connect second right), continuing to slot 2 to wind the next coil, 2 to 7 ( Fgr. 4.116). Please note that the coils advance in the opposite direction from the path in forming the lead. Thus, retrogressive.

The progressive wind ( FGR. 115) requires the finish wire connection third bar right, and continues to slot 12 for the 12-to-5 coil ( FGR. 117).

The index of the armature in FGR. 114 is clockwise (CW), looking at the shaft end (the end opposite the commutator). Indexing the armature CW causes the counterclockwise (CCW) advance of coils.

Armature Polarity

The polarity of the armature becomes obvious with the winding of the second coil.

Tracing the path of current flow away from the positive brush in FGR. 116, through the active coil 2 to 7, the direction through the coil sides within the coil com mutated by the positive brush is away from the commutator.

Fgr. 117 shows the opposite current direction. Therefore, the armature of Fgr. 4.117 will run in the opposite direction from that of FGR. 116.

Note that this discussion is in terms of a steady dc condition. However, the relationship still exists for any instantaneous condition of ac motors. Thus, the same method of analysis is used in both ac and dc universal motors.

Figures 118 and 119 show each armature wind continued to the point of the first overlap. Note in FGR. 118 that two coil sides appear in slot 6, two coil sides appear in slot 1.

Figures 120 and 121 show the addition of coil 7 to 12 (12 to 7 progressive), which coil is opposite the commutated coil 1 to 6.The coil 7 to 12 is commutated by the negative brush while the coil 1 to 6 is commutated by the positive brush.

Fgr. 122 shows the continuance of wind to the first double-overlap coil 8 to 1.

Also, FGR. 123 shows the first double-overlap coil 11 to 6 in place.

Figures 124 and 125 show the wind completed.

FGR. 115 Armature lap winding, first coil progresses: (a) end view, and (b) side view.

FGR. 116 Armature lap winding, second coil retrogresses: (a) end view, and (b) side view. Polarity and connection pattern are now indicated.

FGR. 117 Armature lap winding, second coil progresses: (a) end view, and (b) side view. Polarity and connection pattern are now indicated.

FGR. 118 Armature lap winding, first overlap, coil retrogresses: (a) end view, and (b) side view.

FGR. 119 Armature lap winding, first overlap, coil progresses: (a) end view, and (b) side view.

FGR. 120 Armature lap winding, second commutating coil retrogresses: (a) end view, and (b) side view.

FGR. 121 Armature lap winding, second commutating coil progresses: (a) end view, and (b) side view.

FGR. 122 Armature lap winding, first double over lap, coil retrogresses: (a) end view, and (b) side view.

FGR. 123 Armature lap winding, first double overlap, coil progresses: (a) end view, and (b) side view.

FGR. 124 Armature lap winding, completed progressive wind, coil retrogresses: (a) end view, and (b) side view.

FGR. 125 Armature lap winding, completed progressive wind, coil progresses: (a) end view, and (b) side view.

Anchored Lead Loops

Prior to the late 1950s, most armatures were wound with lead loops which were hand-sorted and laid into slots in the commutator bars. It was necessary for automatic machines to mechanically form such loops in a manner that they would be secure and identifiable.

Several arrangements were used, but the most popular was the anchored loop.

The anchored loop could be formed in several ways, but the usual way was as shown in Ills. 126 through 4.131.The leads might be shifted to the right as shown or to the left, depending upon the requirements.

FGR. 126 Forward pattern anchored lead sequence.

This pattern became known as the forward pattern ( Ills. 134b), and its mirror image ( FGR. 134a) as the reverse pattern. The choice usually depended upon angular brush location and required polarity. Please note that two extra lead wires (canceling each other) appear in each slot.

FGR. 127 Index CCW. FGR. 128 Flier reverse (to commutator end).

FGR. 129 Extending lead hook flier return (to shaft end).

FGR. 131 Repeating second loop (com pare to FGR. 117).

FGR. 130 Winding second coil.

Selection for Polarity

The key items controlling polarity are (1) brushes, (2) direction of wind, and (3) direction of index. Changing any one of these will reverse the polarity. mReversing any two (like a double negative) will keep the polarity the same. Changing all three will reverse the polarity. Please note that in this latter instance the brush locations are out of line from the poles, as is the usual case.

Variations of the anchored loop were often used for convenience.

FGR. 132 Polarity of winding connections, opposite polarity: (a) forward pattern, and (b) for ward pattern.

FGR. 133 Polarity of winding connections, same polarity: (a) reverse pattern, and (b) forward pattern.

FGR. 134 Polarity of winding connections, brush location 90° to left: (a) reverse pattern, and (b) forward pattern.

Starting Wire Connection

While the wire starting at the shaft end has not been shown as connected in Fgr. 126, in practice it was finally laid toward the commutator in slot 5, along with a finish wire, and connected to the bar preceding the first loop.

Tang-Type Commutators

In the late 1950s, the tang hook on the commutator bar became popular. Simultaneously, the hot-staking method became practical. In this method, the finish wire (or lead loop) was laid over the selected tang, by the flier, and the subsequent coil was then wound. There was no chance to remove the insulation from the wire to permit soldering. Therefore, the hot-staking method of pressure and heat application disintegrated the insulation and pressed the tang tightly around the lead. Good electrical contact was thus possible.

Another difficulty was the unsupported wire extending from the coil to the tang.

Winding subsequent coils tended to stretch and even break that wire. The first application involved heavy wire which could withstand this pressure. For fine wire, a pat tern was selected wherein the lead was connected at a tang sufficiently removed so that the wire laid tangent to the shaft.

A third problem was shorts at the crossovers of the leads which approached and left the tangs (see FGR. 125). The anchoring pattern ( FGR. 131) solved both these latter problems in most instances.

Typical Polarity Matching

Two basic winds, with brushes shifted from pole centerline, are shown in FGR. 135.

The standard forward and reverse patterns are shown as adapted to match Fgr. 136.

Special anchored loop patterns, in which loops are drawn before indexing, are shown in FGR. 137.

Fgr. 138 shows front leads drawn to distant tangs where they will be sup ported by tangent contact with the shaft. A special armature diverter is used to spin the armature, presenting the proper tang, and then return to the original position for normal indexing when engaging the lead.

FGR. 135 Automotive winding patterns: (a) retrogressive, and (b) progressive.

A recently developed arrangement involves carrying the lead wire almost halfway around the shaft, engaging the tang with a reverse wrap (alpha connection), and then continuing around the shaft to a slot advanced (fwd) or retracted (rev) from the previous coil ( FGR. 139).All conditions can be met with LFTC wind and CCW armature rotation, requiring only the proper tang selection and progressed (fwd) or retrogressed (rev) slot selection. The leads are anchored around the shaft, not taking extra wire and slot space for the anchoring turn, and with the alpha connection giving safe crossover locations in the lead system.

It should be noted that winding over tangs, as in Ills. 4.136a and 4.137b, becomes difficult because, when reversing the flier, the wire does not follow the form into the slot, requiring an extra guide provision. However, Ills. 4.136b and 4.137a, represent patterns in which the wire is guided into the slot by the form.

Double-Flier Winding

The foregoing discussion presents the principles used by the single-flier winding apparatus. Double-flier winding uses all these principles in duplicate. Fgr. 140 shows the winding of coils 1 to 6 and 7 to 12 simultaneously. Fgr. 141 shows the winding of coils 2 to 7 and 8 to 1 after CW indexing.

FGR. 136 Standard anchored-lead winding patterns: (a) forward pattern, and (b) reverse pattern.

FGR. 137 Special anchored-lead winding patterns: (a) reverse pattern, and (b) forward pattern.

FGR. 138 Tangential front-lead winding patterns: (a) reverse pattern, and (b) forward pattern.

FGR. 139 Alpha-connected shaft-anchored-lead winding patterns: (a) forward pattern, and (b) reverse pattern.

FGR. 140 Double-flier balanced wind: first wind.

FGR. 141 Double-flier balanced wind: second wind.

Odd Slot in Double-Flier Winding

It’s necessary to reduce an odd-slot to an even-slot wind by winding one coil alone, leaving an even number of coils to be wound using both fliers. In Globe winders, the right flier is disengaged while the left flier winds out the odd coil. Then the right flier reengages to complete the winding.

Fgr. 142 shows that the coil 1 to 6 was wound first; then coils 2 to 7 and 7 to 1 were simultaneously wound. In this instance the coil span is 1/2 slot short of diametric. However, in rare instances, the pitch is 1 1/2 slots short of diametric, as shown in FGR. 143. Less copper is used, but poorer commutating is experienced. However, in this case the winding forms are offset and, for CW indexing, are closer together at the top than at the bottom; while for CCW indexing, they are closer together at the bottom.

Two Coils Per Slot

In appliance motors (110 or 220 V), a larger number of bars and coils is desired to keep the voltage between bars down. Without increasing the number of slots, the bars can be doubled by winding a first coil, pulling a lead, then winding a second coil in the same slot ( FGR. 144). Matching this involves the two-coil forward pattern ( FGR. 145).

Note that in forming the lead, after the first coil 2 to 7, a reverse (CW) index is used so that the loop emerging from slot 1 returns from the hook into slot 2, thus to wind the second 2-to-7 coil. This is referred to as a straddle loop and usually is formed shorter than the next (straight) loop, whose sides both emerge from slot 2.

Thus, when pulled as a lead loop, it can be readily identified.

Fgr. 146 illustrates the alpha-connected shaft-anchored pattern equivalent (called the alpha pattern for short).

FGR. 142 Odd slot: coil 1 to 6 wound first, then coils 2 to 7 and 7 to 1 wound simultaneously.

FGR. 143 Odd slot: pitch is 1 1/2 short of diametric.

FGR. 144 Two coils per slot LFTC index CW.

FGR. 146 Two-coil progressive (fwd) alpha-connected shaft-anchored pattern.

FGR. 145 Two-coil forward pattern.

Opposite Brush Selection

When the proposed Globe winding involves connecting to the opposite brush from the customer's sample or design, this is done by connecting to a commutation segment located 180° from that to which the sample is connected.

However, odd-slot armatures having only one coil per slot won’t have a commutator segment at the 180° position. For instance, a 15-slot armature would have segments at 168° or 192° from the sample connected segment. The coil would be commutated either 12° early or 12° late if connected to one of these "opposite" segments. Brush sparking and loss of power would result from this displacement.

The solution is for the customer to compensate by placing the commutator at 1/2 slot change in location so a segment will be at the 180° location for the selected pat tern.

When two coils per slot are involved, or when even-slot armatures are involved, there will be a segment at this 180° location, and no special commutator location need be requested.

Four-Pole Armatures

The foregoing discussion concerns two-pole armatures with the start and finish of each coil connected to adjacent segments. The two-pole designation means that the coil sides are in nearly opposite slots; the result being that the windings naturally draw in toward the bottom of the slots. The adjacent segment connection means that the armature is lap wound.

The vast majority of small-appliance and tool motor armatures fall into this classification. However, many slower-speed or heavier duty motors have four or more poles. Also, a different connection pattern (known as wave connection) may be used.

It’s not the intent here to weigh the relative merits of two-pole versus four-pole armatures, nor the merits of wave versus lap connections. Rather, you must be able to understand how to analyze a design you encounter, so you can determine how the equipment can wind it or its equivalent. In recommending an equivalent, you have the opportunity to accommodate desirable features and attachments.

Winding Pitch. Each armature coil is wound with its sides in slots spaced approximately one pole span, and this is just the same kind of span as in the two-pole armatures. This is fundamental because a coil must be commutated while its coil sides are passing between poles, with one side coming out from under one polarity pole while the other side comes out from under an opposite polarity pole.

Thus, in a 17-slot 4-pole armature, the coil pitch would be 1 to 5 (4 slot spans) or just less than 90° mechanical; see FGR. 147. Please note that this is just less than 180° electrical, since there are 720° electrical in a four-pole motor.

This is obvious from the end (upper) view, sometimes called the "rose" pattern.

The periphery (360° mechanical) includes two pairs of poles, each of which pair pro vides 360° electrical.

Obviously, a quarter-span coil will draw against the sides of the slots instead of toward the bottom. Special tooling design and wire handling is necessary to fill the slots of this coil span. The problem is greater if six or more poles are involved.

Wave Versus Lap Winding. Lap winding is illustrated in FGR. 115 (and all the foregoing figures); the finish wire is connected to the first bar forward of its starting wire. In the 12-slot, 1-coil-per-slot armature, this would be 30° electrical forward of its start. This is progressive lap winding. However, in FGR. 114, the finish lead connects to the first bar back, or 30° electrical back of its start, which is retrogressive lap winding.

Referring to FGR. 147, the four-pole progressive lap wind finish again connects to the first bar forward of its start. The wave connection has the start and finish leads connected approximately 360° electrical apart instead of adjacent. When the finish is connected 360° electrical forward to the first bar forward, as shown in FGR. 148, it’s a progressive wave-wound connection.

Fgr. 149 is different in that the coils as shown in the (lower) spread pattern are wound clockwise instead of counterclockwise as in FGR. 148.Note that the start wire enters slot 7 of coil 3 to 7, emerging from slot 3; the finish connects to the first bar back of 360° electrical and is a retrogressive wave winding. From there it continues, entering slot 15, emerging from slot 11, and connecting one bar back of the start to 7.

FGR. 147 Lap progressive conventional pattern: (a) end view, and (b) side view.

FGR. 148 Wave progressive conventional pattern: (a) end view, and (b) side view.

FGR. 149 Wave retrogressive globe shaft-anchored pattern:

(a) end view, and (b) side view.

Polarity. Note that FGR. 148, which shows a conventional winding, is matched in polarity by FGR. 149, in which the lead will lie against the shaft for support and can be wound with the Alpha connection and the shaft-anchored pattern. The alpha rotator mechanism, when provided with a set of four-pole wave cams, provides the index for this family of four-pole wave windings according to the shaft-anchored pattern of FGR. 149, whether progressive or retrogressive.

Keep in mind that in the rose pattern (end view), only the ends of the coil sides are seen. Current flowing from the positive brush (1), FGR. 148, enters slot 4 going away and is represented by the X as the feather-end of an arrow. Returning in the other coil side, in slot 8, it’s represented by a dot as the front tip of an approaching arrow. Note that the current continues to bar 10, and then to coil 13 to 17, and so on.

The spread pattern is shown fully developed, corresponding respectively to Ills. 147, 4.148, and 149.The commutator is shifted 1/2 slot in FGR. 149 (also in FGR. 152) to maintain commutation performance for this retrogressive wind. Note that coils 3 to 7 and 11 to 15 are commutating instead of coils 3 to 7 and 12 to 16, as in the progressive wind of FGR. 148. Such a shift in the commutator is often required when using an alternate winding pattern in an odd slot armature.

FGR. 150 Four-pole lap wind progressive conventional pattern.

FGR. 151 Wave wind progressive conventional pattern.

FGR. 152 Wave wind retrogressive globe shaft-anchored pattern.

Brushes. In lap windings a brush is needed for each pole in order to commutate all of the coils as they move from pole to pole. Thus, a pair of brushes is needed for a two-pole lap, two pairs for a four-pole lap, etc.

In wave windings, however, with an odd number of slots, all coils can be commutated as they move from pole to pole by a single pair of brushes regardless of whether there are four or six poles, or more. The proof of this is that when tracing through two coils in series on a four-pole (three coils in series on a six-pole, etc.) armature. The finish lead connects to the next bar to the start lead. It will be to the next beyond for progressive wind or next back for retrogressive wind.

Note that if you continue to trace the circuit through all the coils in series, the finish from the last coil will connect to the start of the first coil. This is as though the entire group of coils was wound by one single uncut wire whose finish connects to its start.

This is not so, however, if there is an even number of slots. When tracing through two coils of an even-slot four-pole wave (three coils of a six-pole, etc.), the finish will connect incorrectly to the same bar as its start, or correctly to the second bar away, depending on the lead span (look forward to see the special cases in Ills. 163 through 4.168).

Four brushes will be required to commutate the necessary coils in a four-pole, even-slot, wave-wound armature.

Automatic Winding. For automated winding and connecting, the consecutive coils of a wave pattern are not in adjacent pairs of slots. Instead, the winder must lay the finish wire of a coil on the designated commutator tang, then index to the coil slot into which the wire leaving that same tang must go.

For instance after starting on bar 16 ( FGR. 148), coil 2 to 6 would be wound. The finish must be laid on tang 8, then indexed to wind coil 11 to 15, then connected to tang 17, and so on.

Single-Flier Winding. In a single-flier winder, the four-pole odd-slot armatures could be completely wound in a regular pattern as previously discussed and as indicated in Ills. 153 through 4.158 (neglecting the dotted line designation). In other words, after proceeding in the described pattern through 17 coils ( Ills. 157 and 158), the finish wire will attach in the regular pattern to the same tang to which the original start was connected. Figures 4.159 and 4.160 show 19-slot 1-5 pitch 4-pole retrogressive and progressive windings, respectively.

FGR. 153 Four-pole odd-slot retrogressive winding: 13 slot, 1-4 pitch.

FGR. 154 Four-pole odd-slot progressive winding: 13 slot, 1-4 pitch.

FGR. 155 Four-pole odd-slot retrogressive winding: 15 slot, 1-4 pitch.

FGR. 156 Four-pole odd-slot progressive winding: 15 slot, 1-4 pitch.

FGR. 157 Four-pole odd-slot retrogressive winding: 17 slot, 1-5 pitch.

FGR. 158 Four-pole odd-slot progressive winding: 17 slot, 1-5 pitch.

FGR. 159 Four-pole odd-slot retrogressive winding: 19 slot, 1-5 pitch.

FGR. 160 Four-pole odd-slot progressive winding: 19 slot, 1-5 pitch.

This is also true of four-pole even-slot armatures, if the slots are in multiples of 4 (see Ills. 4.161 and 4.162; also Ills. 4.165 and 4.166).However, after winding 7 coils of a 14-slot 4-pole armature ( FGR. 163), the finish of that seventh coil would fall on the same tang as the start of its first coil. Then an irregularity must be programmed to tie off that lead, move to the next adjacent tang with a new start, wind in the inter mediate coils in the same regular pattern, and thus complete the armature.

Double-Flier Winding. Very readily it can be seen that the even-slot four-pole armatures lend themselves to double-flier winding.

In Ills. 163 through 168, the solid line shows the windings from the left flier, while the dotted line shows those for the right flier. In the center of each rose, the short center lines indicate the axis of each of the two first coils. In other words, these are the centerlines of the two winding forms at the start.

The pattern shows one flier to progress or retrogress, always skipping a coil space.

The other flier places coils into those skipped spaces to simultaneously complete the winding.

This is not true in odd-slot four-pole windings. At about halfway through the pro gram, one flier will start laying a coil over one previously wound by the other flier if the skipping plan is followed.

Figures 153 through 158 show normal progression, wherein the left flier winds the first coil then progresses to the coil marked 2 at the centerline angle shown. The right flier then can start at the centerline shown for it by the dotted line. With the forma at this quadrature position, the windings can be simultaneously completed in the usual fashion.

FGR. 161 Four-pole even-slot retrogressive winding: 20 slot, 1-6 pitch.

FGR. 163 Four-pole even-slot retrogressive winding: 14 slot, 1-4 pitch.

FGR. 162 Four-pole even-slot progressive winding: 20 slot, 1-6 pitch.

FGR. 165 Four-pole even-slot retrogressive winding: 16 slot, 1-5 pitch.

FGR. 164 Four-pole even-slot progressive winding: 14 slot, 1-4 pitch.

Special off-center tooling must be developed to match this quadrature spacing to the opposed spindles of a double-flier winder. One solution is to wind two separate armatures in single-flier fashion in the double-flier machine.

Translation from Lap to Wave Winding. In some instances, the lap design can be converted to an equivalent wave pattern with the advantage of supporting the leads against the shaft. Also, an improvement is possible in making the alpha connection to the commutator tang.

Fgr. 169 shows a 16-slot lap winding pitched 1 to 5, with connections directly out from the coil in the usual pattern.

Fgr. 170 shows the exact wave equivalent using the alpha connection and shaft-anchored lead, which is possible using the alpha rotator with special four-pole wave cams.

Similarity in Two-Pole and Four-Pole Patterns. Fgr. 171 shows the schematic spread pattern of the two-pole alpha-connected shaft-anchored patented arrangement.

Fgr. 172 shows the similar four-pole pattern. Note that duplicate brushes are used in tandem for commutating and that the coils become tandem in effect to con form to the four poles in the stator.

However, comparing the two-pole ( FGR. 171) to only 360° electrical (half) of the four-pole ( FGR. 172), and recognizing that two negative brushes, even though separate, are one and the same in polarity, the two patterns become fully equivalent.