Commutator (electric)

This article is about the electrical component. For math-ematical concept, see Commutator .A commutator is the moving part of a rotary electrical

Commutator in a universal motor from a vacuum cleaner. Parts:(A) commutator, (B) brush, (C) rotor (armature) windings, (D)stator (field) windings, (E) brush guides

switch in certain types of electric motors and electricalgenerators that periodically reverses the current directionbetween the rotor and the external circuit. It consists of acylinder composed of multiple metal contact segments onthe rotating armature of the machine. The commutatoris one component of a motor; there are also two or morestationary electrical contacts called "brushes" made of asoft conductor like carbon press against the commutator,making sliding contact with successive segments of thecommutator as it rotates. The windings (coils of wire) onthe armature are connected to the commutator segments.Commutators are used in direct current (DC) machines:dynamos (DC generators) and many DC motors as wellas universal motors. In a motor the commutator applieselectric current to the windings. By reversing the cur-rent direction in the rotating windings each half turn, asteady rotating force (torque) is produced. In a genera-tor the commutator picks off the current generated in thewindings, reversing the direction of the current with eachhalf turn, serving as a mechanical rectifier to convert thealternating current from the windings to unidirectionaldirect current in the external load circuit. The first di-rect current commutator-type machine, the dynamo, wasbuilt by Hippolyte Pixii in 1832, based on a suggestion byAndré-Marie Ampère.Commutators are relatively inefficient, and also requireperiodic maintenance such as brush replacement. There-fore, commutated machines are declining in use, be-ing replaced by alternating current (AC) machines, andin recent years by brushless DC motors which usesemiconductor switches.

1 Principle of operation

A commutator consists of a set of contact bars fixed tothe rotating shaft of a machine, and connected to the ar-mature windings. As the shaft rotates, the commutatorreverses the flow of current in a winding. For a single ar-mature winding, when the shaft has made one-half com-plete turn, the winding is now connected so that currentflows through it in the opposite of the initial direction. Ina motor, the armature current causes the fixed magneticfield to exert a rotational force, or a torque, on the wind-ing to make it turn. In a generator, the mechanical torqueapplied to the shaft maintains the motion of the armaturewinding through the stationary magnetic field, inducing acurrent in the winding. In both the motor and generatorcase, the commutator periodically reverses the directionof current flow through the winding so that current flow inthe circuit external to the machine continues in only onedirection.

1.1 Simplest practical commutator

Practical commutators have at least three contact seg-ments, to prevent a “dead” spot where two brushes simul-taneously bridge only two commutator segments. Brushesare made wider than the insulated gap, to ensure thatbrushes are always in contact with an armature coil. Forcommutators with at least three segments, although therotor can potentially stop in a position where two com-

1

2 3 BRUSH CONSTRUCTION

mutator segments touch one brush, this only de-energizesone of the rotor arms while the others will still functioncorrectly. With the remaining rotor arms, a motor canproduce sufficient torque to begin spinning the rotor, anda generator can provide useful power to an external cir-cuit.

2 Ring/segment construction

Cross-section of a commutator that can be disassembled forrepair.[1]

A commutator consists of a set of copper segments, fixedaround the part of the circumference of the rotating ma-chine, or the rotor, and a set of spring-loaded brushesfixed to the stationary frame of the machine. Two ormore fixed brushes connect to the external circuit, eithera source of current for a motor or a load for a generator.Commutator segments are connected to the coils of thearmature, with the number of coils (and commutator seg-ments) depending on the speed and voltage of the ma-chine. Large motors may have hundreds of segments.Each conducting segment of the commutator is insulatedfrom adjacent segments. Mica was used on early ma-chines and is still used on large machines. Many otherinsulating materials are used to insulate smaller machines;plastics allow quick manufacture of an insulator, for ex-ample. The segments are held onto the shaft using adovetail shape on the edges or underside of each segment.Insulating wedges around the perimeter of each segmentare pressed so that the commutator maintains its mechan-ical stability throughout its normal operating range. Com-mutator is used to collect current from armature conduc-

tor.In small appliance and tool motors the segments are typ-ically crimped permanently in place and cannot be re-moved. When the motor fails it is discarded and re-placed. On large industrial machines (say, from severalkilowatts to thousands of kilowatts in rating) it is eco-nomical to replace individual damaged segments, and sothe end-wedge can be unscrewed and individual segmentsremoved and replaced. Replacing the copper and micasegments is commonly referred to as “refilling”. Refill-able dovetailed commutators are the most common con-struction of larger industrial type commutators, but refill-able commutators may also be constructed using exter-nal bands made of fiberglass (glass banded construction)or forged steel rings (external steel shrink ring type con-struction and internal steel shrink ring type construction).Disposable, molded type commutators commonly foundin smaller DC motors are becoming increasingly morecommon in larger electric motors. Molded type commu-tators are not repairable and must be replaced if dam-aged. In addition to the commonly used heat, torque, andtonnage methods of seasoning commutators, some highperformance commutator applications require a more ex-pensive, specific “spin seasoning” process or over-speedspin-testing to guarantee stability of the individual seg-ments and prevent premature wear of the carbon brushes.Such requirements are common with traction, military,aerospace, nuclear, mining, and high speed applicationswhere premature failure can lead to serious negative con-sequences.Friction between the segments and the brushes eventu-ally causes wear to both surfaces. Carbon brushes, be-ing made of a softer material, wear faster and may bedesigned to be replaced easily without dismantling themachine. Older copper brushes caused more wear to thecommutator, causing deep grooving and notching of thesurface over time. The commutator on small motors (say,less than a kilowatt rating) is not designed to be repairedthrough the life of the device. On large industrial equip-ment, the commutator may be re-surfaced with abrasives,or the rotor may be removed from the frame, mounted ina largemetal lathe, and the commutator resurfaced by cut-ting it down to a smaller diameter. The largest of equip-ment can include a lathe turning attachment directly overthe commutator.

3 Brush construction

Early machines used brushes made from strands of cop-per wire to contact the surface of the commutator. How-ever, these hard metal brushes tended to scratch andgroove the smooth commutator segments, eventually re-quiring resurfacing of the commutator. As the copperbrushes wore away, the dust and pieces of the brush couldwedge between commutator segments, shorting them andreducing the efficiency of the device. Fine copper wire

3.1 Brush holders 3

A tiny 5-segment commutator less than 2 mm in diameter, on adirect-current motor in a toy radio control ZipZaps car.

Various types of copper and carbon brushes.[2]

mesh or gauze provided better surface contact with lesssegment wear, but gauze brushes were more expensivethan strip or wire copper brushes.Modern rotating machines with commutators almost ex-clusively use carbon brushes, which may have copperpowder mixed in to improve conductivity. Metallic cop-per brushes can be found in toy or very small motors, suchas the one illustrated above, and some motors which onlyoperate very intermittently, such as automotive startermotors.Motors and generators suffer from a phenomenon knownas 'armature reaction', one of the effects of which is tochange the position at which the current reversal throughthe windings should ideally take place as the loadingvaries. Early machines had the brushes mounted on a ringthat was provided with a handle. During operation, it wasnecessary to adjust the position of the brush ring to adjustthe commutation to minimise the sparking at the brushes.This process was known as 'rocking the brushes’.Various developments took place to automate the processof adjusting the commutation and minimizing the spark-ing at the brushes. One of these was the development of'high resistance brushes’, or brushes made from a mix-ture of copper powder and carbon.[3] Although describedas high resistance brushes, the resistance of such a brushwas of the order of milliohms, the exact value dependenton the size and function of the machine. Also, the high

resistance brush was not constructed like a brush but inthe form of a carbon block with a curved face to matchthe shape of the commutator.The high resistance or carbon brush is made large enoughthat it is significantly wider than the insulating segmentthat it spans (and on large machines may often span twoinsulating segments). The result of this is that as the com-mutator segment passes from under the brush, the cur-rent passing to it ramps down more smoothly than hadbeen the case with pure copper brushes where the con-tact broke suddenly. Similarly the segment coming intocontact with the brush has a similar ramping up of thecurrent. Thus, although the current passing through thebrush was more or less constant, the instantaneous cur-rent passing to the two commutator segments was pro-portional to the relative area in contact with the brush.The introduction of the carbon brush had convenient sideeffects. Carbon brushes tend to wear more evenly thancopper brushes, and the soft carbon causes far less dam-age to the commutator segments. There is less spark-ing with carbon as compared to copper, and as the car-bon wears away, the higher resistance of carbon results infewer problems from the dust collecting on the commu-tator segments.The ratio of copper to carbon can be changed for a par-ticular purpose. Brushes with higher copper content per-form better with very low voltages and high current, whilebrushes with a higher carbon content are better for highvoltage and low current. High copper content brushestypically carry 150 to 200 amperes per square inch ofcontact surface, while higher carbon content only car-ries 40 to 70 amperes per square inch. The higher re-sistance of carbon also results in a greater voltage drop of0.8 to 1.0 volts per contact, or 1.6 to 2.0 volts across thecommutator.[4]

3.1 Brush holders

A spring is typically used with the brush, to maintain con-stant contact with the commutator. As the brush andcommutator wear down, the spring steadily pushes thebrush downwards towards the commutator. Eventuallythe brush wears small and thin enough that steady contactis no longer possible or it is no longer securely held in thebrush holder, and so the brush must be replaced.It is common for a flexible power cable to be directly at-tached to the brush, because current flowing through thesupport spring would cause heating, which may lead to aloss of metal temper and a loss of the spring tension.When a commutated motor or generator uses more powerthan a single brush is capable of conducting, an assemblyof several brush holders is mounted in parallel across thesurface of the very large commutator.This parallel holder distributes current evenly across allthe brushes, and permits a careful operator to remove a

4 3 BRUSH CONSTRUCTION

Compound carbon brush holder, with individual clamps and ten-sion adjustments for each block of carbon.[5]

bad brush and replace it with a new one, even as the ma-chine continues to spin fully powered and under load.High power, high current commutated equipment is nowuncommon, due to the less complex design of alternatingcurrent generators that permits a low current, high voltagespinning field coil to energize high current fixed-positionstator coils. This permits the use of very small singularbrushes in the alternator design. In this instance, the ro-tating contacts are continuous rings, called slip rings, andno switching happens.Modern devices using carbon brushes usually have amaintenance-free design that requires no adjustmentthroughout the life of the device, using a fixed-positionbrush holder slot and a combined brush-spring-cable as-sembly that fits into the slot. The worn brush is pulled outand a new brush inserted.

3.2 Brush contact angle

The different brush types make contact with the com-mutator in different ways. Because copper brushes havethe same hardness as the commutator segments, the ro-tor cannot be spun backwards against the ends of cop-per brushes without the copper digging into the segmentsand causing severe damage. Consequently, strip/laminatecopper brushes only make tangential contact with thecommutator, while copper mesh and wire brushes use aninclined contact angle touching their edge across the seg-ments of a commutator that can spin in only one direction.The softness of carbon brushes permits direct radial end-contact with the commutator without damage to the seg-

Brush angle definitions[6]

Commutator and brush assembly of a traction motor; the copperbars can be seen with lighter insulation strips between the bars.Each dark grey carbon brush has a short flexible copper jumperlead attached. Parts of the motor field winding, in red, can beseen to the right of the commutator.

ments, permitting easy reversal of rotor direction, with-out the need to reorient the brush holders for operationin the opposite direction. Although never reversed, com-mon appliance motors that use wound rotors, commuta-tors and brushes have radial-contact brushes. In the caseof a reaction-type carbon brush holder, carbon brushesmay be reversely inclined with the commutator so thatthe commutator tends to push against the carbon for firmcontact.

4.2 Further compensation for self-induction 5

4 The commutating plane

Commutating plane definitions.[7]

The contact point where a brush touches the commuta-tor is referred to as the commutating plane. To conductsufficient current to or from the commutator, the brushcontact area is not a thin line but instead a rectangularpatch across the segments. Typically the brush is wideenough to span 2.5 commutator segments. This meansthat two adjacent segments are electrically connected bythe brush when it contacts both.

4.1 Compensation for stator field distor-tion

Normal Neutral Plane

Normal Plane ofMaximum Induction

S NG H

E

F

Centered position of the commutating plane if there were no fielddistortion effects.[8]

Most introductions to motor and generator design startwith a simple two-pole device with the brushes arranged

at a perfect 90-degree angle from the field. This ideal isuseful as a starting point for understanding how the fieldsinteract but it is not how a motor or generator functionsin actual practice.In a real motor or generator, the field around the rotor isnever perfectly uniform. Instead, the rotation of the rotorinduces field effects which drag and distort the magneticlines of the outer non-rotating stator.

Normal Neutral Plane

Normal Planeof Maximum

Induction

S N

ActualNeutralPlane

Actual Plane ofMaximum InductionS'

N'

D

RY

Actual position of the commutating plane to compensate for fielddistortion.[11]

The faster the rotor spins, the further this degree of fielddistortion. Because a motor or generator operates mostefficiently with the rotor field at right angles to the statorfield, it is necessary to either retard or advance the brushposition to put the rotor’s field into the correct position tobe at a right angle to the distorted field.These field effects are reversed when the direction ofspin is reversed. It is therefore difficult to build an ef-ficient reversible commutated dynamo, since for highestfield strength it is necessary to move the brushes to theopposite side of the normal neutral plane.The effect can be considered to be analogous to timingadvance in an internal combustion engine. Generally adynamo that has been designed to run at a certain fixedspeed will have its brushes permanently fixed to align thefield for highest efficiency at that speed.[12]

4.2 Further compensation for self-induction

Self-induction – The magnetic fields in each coil of wirejoin and compound together to create amagnetic field thatresists changes in the current, which can be likened to thecurrent having inertia.In the coils of the rotor, even after the brush has beenreached, currents tend to continue to flow for a brief mo-ment, resulting in a wasted energy as heat due to thebrush spanning across several commutator segments and

6 6 REPULSION INDUCTION MOTORS

Brush advance for Self-Induction.[13]

the current short-circuiting across the segments.Spurious resistance is an apparent increase in the resis-tance in the armature winding, which is proportional tothe speed of the armature, and is due to the lagging ofthe current.To minimize sparking at the brushes due to this short-circuiting, the brushes are advanced a few degrees furtheryet, beyond the advance for field distortions. This movesthe rotor winding undergoing commutation slightly for-ward into the stator field which has magnetic lines in theopposite direction and which oppose the field in the sta-tor. This opposing field helps to reverse the lagging self-inducting current in the stator.So even for a rotor which is at rest and initially requires nocompensation for spinning field distortions, the brushesshould still be advanced beyond the perfect 90-degree an-gle as taught in so many beginners textbooks, to compen-sate for self-induction.

5 Limitations and alternatives

Although direct current motors and dynamos once domi-nated industry, the disadvantages of the commutator havecaused a decline in the use of commutated machines inthe last century. These disadvantages are:

• Due to friction, the brushes and copper commuta-tor segments wear out. In small consumer productssuch as power tools and appliances the brushes maylast as long as the product, but larger machines re-quire regular replacement of brushes and occasionalresurfacing of the commutator. So commutated ma-chines are not used in equipment at remote locationsthat must operate for long periods without mainte-nance.

• The resistance of the sliding contact between brush

Low voltage dynamo from late 1800s for electroplating. The re-sistance of the commutator contacts causes inefficiency in lowvoltage, high current machines like this, requiring a huge elabo-rate commutator. This machine generated 7 volts at 310 amps.

and commutator causes a voltage drop called the“brush drop”. This may be several volts, so it cancause large power losses in low voltage, high cur-rent machines. The friction of the brush against thecommutator also absorbs some of the energy of themachine. Alternating current motors, which do notuse commutators, are much more efficient.

• There is a limit to the maximum current density andvoltage which can be switched with a commutator.Very large direct current machines, say, more thanseveral megawatts rating, cannot be built with com-mutators. The largest motors and generators are allalternating-current machines.

• The switching action of the commutator can causesparking at the contacts, generating electromagneticinterference.

With the wide availability of alternating current, DCmotors have been replaced by more efficient ACsynchronous or induction motors. In recent years, withthe widespread availability of power semiconductors, inmany remaining appications commutated DC motorshave been replaced with "brushless direct current mo-tors". These don't have a commutator; instead the di-rection of the current is switched electronically. A sen-sor keeps track of the rotor position and semiconductorswitches such as transistors reverse the current. Operat-ing life of these machines is much longer, limited mainlyby bearing wear.

6 Repulsion induction motors

These are single-phase AC-only motors with higher start-ing torque than could be obtained with split-phase start-ing windings, before high-capacitance (non-polar, rel-

7

atively high-current electrolytic) starting capacitors be-came practical. They have a conventional wound statoras with any induction motor, but the wire-wound rotor ismuch like that with a conventional commutator. Brushesopposite each other are connected to each other (not to anexternal circuit), and transformer action induces currentsinto the rotor that develop torque by repulsion.One variety, notable for having an adjustable speed, runscontinuously with brushes in contact, while another usesrepulsion only for high starting torque and in some caseslifts the brushes once the motor is running fast enough.In the latter case, all commutator segments are connectedtogether as well, before the motor attains running speed.Once at speed, the rotor windings become functionallyequivalent to the squirrel-cage structure of a conventionalinduction motor, and the motor runs as such.[14]

7 Laboratory commutators

Commutators were used as simple forward-off-reverseswitches for electrical experiments in physics laborato-ries. There are two well-known historical types:[15]

7.1 Ruhmkorff commutator

This is similar in design to the commutators used in mo-tors and dynamos. It was usually constructed of brass andivory (later ebonite).[16]

7.2 Pohl commutator

This consisted of a block of wood or ebonite with fourwells, containing mercury, which were cross-connectedby copper wires. The output was taken from a pair ofcurved copper wires which were moved to dip into one orother pair of mercury wells.[17] Instead of mercury, ionicliquids or other liquid metals could be used.

8 See also

• Armature (electrical engineering)

• Slip ring

• Rotary transformer

• Mercury swivel commutator

• Brushless motor

• File:Kommutator animiert.gif

9 Patents

• Elihu Thomson - U.S. Patent 242,488 - Commuta-tors for Dynamo Electric Machines - 1881 June 7.

• Henry Jacobs - U.S. Patent 246,612 - Commutatorfor Magneto Electric Machines - 1881 September 6.

• Frank. B. Rae & Clarence. L. Healy - U.S. Patent294,270 - Commutator For Dynamo or MagnetoElectric Machines - 1884 February 26.

• Nikola Tesla - U.S. Patent 334,823 - Commutatorfor Dynamo Electric Machines - 1886 January 26.

• Thomas E. Adams - U.S. Patent 340,537 - Commu-tator for Dynamo-Electric Machines - 1886April 27.

• Nikola Tesla - U.S. Patent 382,845 - Commutatorfor Dynamo Electric Machines - 1888 May 15.

10 References[1] Hawkins Electrical Guide, Theo. Audel and Co., 2nd ed.

1917, vol. 1, ch. 21: Brushes and the Brush Gear, p. 300,fig. 327

[2] Hawkins Electrical Guide, Theo. Audel and Co., 2nd ed.1917, vol. 1, ch. 21: Brushes and the Brush Gear, p. 304,fig. 329-332

[3] Higher Electrical Engineering: Shepherd, Morton &Spence

[4] Hawkins Electrical Guide, Theo. Audel and Co., 2nd ed.1917, vol. 1, ch. 21: Brushes and the Brush Gear, p. 313

[5] Hawkins Electrical Guide, Theo. Audel and Co., 2nd ed.1917, vol. 1, ch. 21: Brushes and the Brush Gear, p. 307,fig. 335

[6] Hawkins Electrical Guide, Theo. Audel and Co., 2nd ed.1917, vol. 1, ch. 21: Brushes and the Brush Gear, p. 312,fig. 339

[7] Hawkins Electrical Guide, Theo. Audel and Co., 2nd ed.1917, vol. 1, ch. 20: Commutation and the Commutator,p. 284, fig. 300

[8] Hawkins Electrical Guide, Theo. Audel and Co., 2nd ed.1917, vol. 1, ch. 20: Commutation and the Commutator,p. 285, fig. 301

[9] Hawkins Electrical Guide, Theo. Audel and Co., 2nd ed.1917, vol. 1, ch. 20: Commutation and the Commutator,p. 264, fig. 286

[10] Hawkins Electrical Guide, Theo. Audel and Co., 2nd ed.1917, vol. 1, ch. 20: Commutation and the Commutator,p. 265, fig. 287

[11] Hawkins Electrical Guide, Theo. Audel and Co., 2nd ed.1917, vol. 1, ch. 20: Commutation and the Commutator,p. 286, fig. 302

8 11 EXTERNAL LINKS

[12] Hawkins Electrical Guide, Theo. Audel and Co., 2nd ed.1917, vol. 1, ch. 20: Commutation and the Commutator,p. 285-287

[13] Hawkins Electrical Guide, Theo. Audel and Co., 2nd ed.1917, vol. 1, ch. 20: Commutation and the Commutator,p. 287, fig. 303

[14] http://www.vias.org/feee/c13_motors_13.html

[15] Hadley, H. E., Magnetism and Electricity for Students,MacMillan, London, 1905, pp 245-247

[16] http://www.fstfirenze.it/collezioni/scientifico_en/isin.asp?Id=0556

[17] http://www.fstfirenze.it/collezioni/scientifico_en/isin.asp?Id=0559

11 External links• "Commutator and Brushes on DC Motor". Hyper-Physics, Physics and Astronomy, Georgia State Uni-versity.

• "PM Brushless Servo Motor Feedback Commuta-tion Series – Part 1 Commutation Alignment – WhyIt Is Important.” Mitchell Electronics.

• "PM Brushless Servo Motor Feedback Commuta-tion Series – Part 2 Commutation Alignment – HowIt Is Accomplished.” Mitchell Electronics.

9

12 Text and image sources, contributors, and licenses

12.1 Text• Commutator (electric) Source: https://en.wikipedia.org/wiki/Commutator_(electric)?oldid=687266377 Contributors: XJaM, Heron,Glenn, GRAHAMUK, Reddi, Zoicon5, Indefatigable, Robbot, Securiger, Ojigiri~enwiki, Dina, Giftlite, Mcapdevila, Gadfium, Gauss,Kjkolb, Wtshymanski, DV8 2XL, Linas, Borb, Cbdorsett, Stixpjr, NCdave, Ian Pitchford, Margosbot~enwiki, Srleffler, Chobot, Wave-length, DMahalko, Gabosgab, Howcheng, Cosmotron, Tabby, Gabemejia, Commander Keane bot, Chris the speller, AndrewBuck, J00tel,JohnGage, Clicketyclack, SashatoBot, Dr.saptarshi, Ex nihil, Dicklyon, Iridescent, Mfrosz, Mathfan, Heywøød, Chetvorno, Thijs!bot,WinBot, BokicaK, JAnDbot, PhilKnight, MSBOT, Nikevich, Destynova, JJ Harrison, CommonsDelinker, Larryisgood, Voorlandt,Tyson.tucker, Biscuittin, Flyer22 Reborn, Hamiltondaniel, ClueBot, Excirial, Alexbot, Dthomsen8, Addbot, Willking1979, SpellingBot,Download, Teles, Luckas-bot, Yobot, TaBOT-zerem, Amirobot, AnomieBOT, Redhandedway, Fredde 99, FrescoBot, Craig Pemberton,Oalp1003, RedBot, Full-date unlinking bot, Steelerdon, EmausBot, John of Reading, Enviromet, Winner 42, GenyAncalagon, Wikfr, Rap-tureBot, Cblambert, ClueBot NG, Jaanus.kalde, Satellizer, Widr, Technical 13, BG19bot, Northamerica1000, AvocatoBot, Nelg, Jimw338,Rezonansowy, Myrrh near, SJ Defender, Dan Mihai Pitea, Mfixerer, Shubham bhilai and Anonymous: 109

12.2 Images• File:Ambox_current_red.svg Source: https://upload.wikimedia.org/wikipedia/commons/9/98/Ambox_current_red.svg License: CC0Contributors: self-made, inspired by Gnome globe current event.svg, using Information icon3.svg and Earth clip art.svg Original artist:Vipersnake151, penubag, Tkgd2007 (clock)

• File:Collecteur_commutateur_rotatif.png Source: https://upload.wikimedia.org/wikipedia/commons/c/c7/Collecteur_commutateur_rotatif.png License: CC-BY-SA-3.0 Contributors: ? Original artist: ?

• File:Commutator-of-DC-traction-motor-01.jpg Source: https://upload.wikimedia.org/wikipedia/commons/2/2a/Commutator-of-DC-traction-motor-01.jpg License: CC BY-SA 3.0 Contributors: Own work Original artist: Rs1421

• File:Commutator_-_Advance_for_Self_Induction.png Source: https://upload.wikimedia.org/wikipedia/commons/5/53/Commutator_-_Advance_for_Self_Induction.png License: Public domain Contributors: ? Original artist: ?

• File:Commutator_-_Brush_Contact_Angle.png Source: https://upload.wikimedia.org/wikipedia/commons/4/4d/Commutator_-_Brush_Contact_Angle.png License: Public domain Contributors: ? Original artist: ?

• File:Commutator_-_Crocker-Wheeler_Carbon_Brush_Gear_(600dpi).png Source: https://upload.wikimedia.org/wikipedia/commons/6/65/Commutator_-_Crocker-Wheeler_Carbon_Brush_Gear_%28600dpi%29.png License: Public domain Contributors: ?Original artist: ?

• File:Commutator_-_Sectional_View.png Source: https://upload.wikimedia.org/wikipedia/commons/7/7c/Commutator_-_Sectional_View.png License: Public domain Contributors: ? Original artist: ?

• File:Commutator_brush_types.png Source: https://upload.wikimedia.org/wikipedia/commons/2/23/Commutator_brush_types.png Li-cense: Public domain Contributors: ? Original artist: ?

• File:Dynamo_-_commutating_plane_definitions.jpg Source: https://upload.wikimedia.org/wikipedia/commons/4/41/Dynamo_-_commutating_plane_definitions.jpg License: Public domain Contributors: ? Original artist: ?

• File:Dynamo_-_commutating_plane_field_distortion.svg Source: https://upload.wikimedia.org/wikipedia/commons/6/60/Dynamo_-_commutating_plane_field_distortion.svg License: CC BY-SA 3.0 Contributors: Own work Original artist: Borb

• File:Dynamo_-_commutating_plane_idealized.svg Source: https://upload.wikimedia.org/wikipedia/commons/1/12/Dynamo_-_commutating_plane_idealized.svg License: CC BY-SA 3.0 Contributors: Own work Original artist: Borb

• File:Dynamo_-_exaggerated_rotating_field_distortion.png Source: https://upload.wikimedia.org/wikipedia/commons/5/5d/Dynamo_-_exaggerated_rotating_field_distortion.png License: Public domain Contributors: ? Original artist: ?

• File:Dynamo_-_iron_filings_show_distorted_field.png Source: https://upload.wikimedia.org/wikipedia/commons/c/ce/Dynamo_-_iron_filings_show_distorted_field.png License: Public domain Contributors: Transferred from en.wikipedia to Commons by Oxyman usingCommonsHelper. Original artist: Nehemiah Hawkins

• File:High-Current_Copper-Brush_Commutated_Dynamo.jpg Source: https://upload.wikimedia.org/wikipedia/commons/7/70/High-Current_Copper-Brush_Commutated_Dynamo.jpg License: Public domain Contributors: ? Original artist: ?

• File:Simplest_Possible_Commutator_-_Brushes.JPG Source: https://upload.wikimedia.org/wikipedia/commons/5/57/Simplest_Possible_Commutator_-_Brushes.JPG License: CC BY-SA 3.0 Contributors: Own work Original artist: DMahalko, Dale Mahalko,Gilman, WI, USA -- Email: dmahalko@gmail.com

• File:Simplest_Possible_Commutator_-_Motor_Body.JPG Source: https://upload.wikimedia.org/wikipedia/commons/e/e3/Simplest_Possible_Commutator_-_Motor_Body.JPG License: CC BY-SA 3.0 Contributors: Own work Original artist: DMahalko, Dale Mahalko,Gilman, WI, USA -- Email: dmahalko@gmail.com

• File:Simplest_Possible_Commutator_-_Rotor_View.JPG Source: https://upload.wikimedia.org/wikipedia/commons/e/e4/Simplest_Possible_Commutator_-_Rotor_View.JPG License: CC BY-SA 3.0 Contributors: Own work Original artist: DMahalko, Dale Mahalko,Gilman, WI, USA -- Email: dmahalko@gmail.com

• File:Tiny_motor_windings_-_commutator_-_brushes_in_Zip_Zaps_toy_R-C_car.jpg Source: https://upload.wikimedia.org/wikipedia/commons/d/dc/Tiny_motor_windings_-_commutator_-_brushes_in_Zip_Zaps_toy_R-C_car.jpg License: CC BY-SA 3.0Contributors: Own work Original artist: Dale Mahalko

• File:Universal_motor_commutator.jpg Source: https://upload.wikimedia.org/wikipedia/commons/f/f1/Universal_motor_commutator.jpg License: Public domain Contributors:

• Original work: MotorCommutator.jpg Original artist:• Original work: Ulfbastel

10 12 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

12.3 Content license• Creative Commons Attribution-Share Alike 3.0