Rotary transformer

Cross-section diagram of a simple rotary transformer.
Prior to the development of the rotary transformer, a slip-ring pickup was used, though this was prone to developing signal noise due to corrosion of the slip rings.

Specialized transformer used to couple electrical signals between two parts that rotate in relation to each other.

- Rotary transformer

7 related topics


Slip ring

Electromechanical device that allows the transmission of power and electrical signals from a stationary to a rotating structure.

Sketch of a cross-section of slip rings for an electric motor. In this example, the slip rings have a brush-lifting device and a sliding contact bar, allowing the slip-rings to be short-circuited when no longer required. This can be used in starting a slip-ring induction motor, for example.
Slip rings on a hydroelectric generator; 
A - stationary spring-loaded graphite brushes, 
B - rotating steel contact ring, 
C - insulated connections to generator field winding, 
D - top end of generator shaft.

Rotary transformers are often used instead of slip rings in high-speed or low-friction environments.

Helical scan

Method of recording high-frequency signals on magnetic tape.

Helical recording method
The head drum of a Hi-Fi NTSC VHS VCR; three of the six heads face the reader. The helical path of the tape around the drum can clearly be seen.
The same head drum with the rotating portion elevated for clarity
The rotating portion of the head drum showing the rotary transformer and three of the six tape heads used in this particular VCR
Type B videotape video scanner head
rotary head visible in a VXA computer tape drive
VXA tape drive, alternate view of rotary head and loading mechanism

Supplying signals to a rotating head is also problematic: This is usually accomplished by coupling the signal(s) inductively through a rotary transformer.


A synchro (also known as selsyn and by other brand names) is, in effect, a transformer whose primary-to-secondary coupling may be varied by physically changing the relative orientation of the two windings.

Schematic of a synchro transducer. The complete circle represents the rotor. The solid bars represent the cores of the windings next to them. Power to the rotor is connected by slip rings and brushes, represented by the circles at the ends of the rotor winding. As shown, the rotor induces equal voltages in the 120° and 240° windings, and no voltage in the 0° winding. [Vex] does not necessarily need to be connected to the common lead of the stator star windings.
Simple two-synchro system.
A picture of a synchro transmitter
View onto the connection description of a synchro transmitter

So-called brushless synchros use rotary transformers (that have no magnetic interaction with the usual rotor and stator) to feed power to the rotor.


Standard for consumer-level analog video recording on tape cassettes.

Top view of a VHS cassette
Top view of a VHS cassette
VHS recorder, camcorder and cassette
JVC HR-3300U Vidstar – the United States version of the JVC HR-3300. It is virtually identical to the Japan version. Japan's version showed the "Victor" name, and did not use the "Vidstar" name.
Top view of VHS with front casing removed
VHS M-loading system.
The interior of a modern VHS VCR showing the drum and tape.
VHS cassette with time scale for SP and LP
This illustration demonstrates the helical wrap of the tape around the head drum, and shows the points where the video, audio and control tracks are recorded.
Panasonic Hi-Fi six-head drum VEH0548 installed on G mechanism as an example, demonstrated a typical VHS head drum containing two tape heads. (1) is the upper head, (2) is the tape heads, and (3) is the head amplifier.
The upper- and underside of a typical four-head VHS head assembly showing the head chips and rotary transformer
Close-up of a head chip
A typical RCA (Model CC-4371) full-size VHS camcorder with a built-in three-inch color LCD screen. The tiltable LCD screen is rare on full-size VHS camcorders; only the smaller VHS-C camcorders are more common to have a tiltable LCD screen on some units.
Victor S-VHS (left) and S-VHS-C (right).
A tape rewinder.
Size comparison between Betamax (top) and VHS (bottom) videocassettes.
A Rasputin Music retailer (Fresno, California) selling used VHS cassettes from 50¢ to $1.98 each for people who still have working VCRs.
Fig Garden Regional Library, a branch of Fresno County Public Library, is giving away their weeded VHS collections for free.
A badly molded VHS tape. Mold can prevent modern use. See Media preservation.

The heads in the rotating drum get their signal wirelessly using a rotary transformer.

Index of electrical engineering articles

Alphabetical list of articles pertaining specifically to electrical and electronics engineering.

Rotary transformer

Alexander M. Poniatoff

American electrical engineer.

Chinese characters (hànzì, 漢字) are morpho-syllabic. Each one represents a syllable with a distinct meaning, but some characters may have multiple meanings or pronunciations

In 1956, Ampex engineers created the world's first rotary head recorder, the VR-1000 videotape recorder.

Science and technology in Russia

Science and technology in Russia have developed rapidly since the Age of Enlightenment, when Peter the Great founded the Russian Academy of Sciences and Saint Petersburg State University and polymath Mikhail Lomonosov founded the Moscow State University, establishing a strong native tradition in learning and innovation.

Shukhov Tower in Moscow.
Mikhail Lomonosov, Russian polymath scientist, inventor, poet and artist, the founder of Moscow State University.
Kunstkamera building, the first headquarters of the Russian Academy of Sciences in Saint Petersburg.
A sculpture in honor of Dmitry Mendeleev and his Periodic table in Slovakia.
The Sukhoi Superjet 100 is the latest civilian product of the Russian aircraft industry.
Rostec headquarters in Moscow
Mir, Soviet and Russian space station that operated in low Earth orbit from 1986 to 2001.

Many famous Russian scientists and inventors were émigrés, like Igor Sikorsky, credited with the invention of the first helicopters, Vladimir Zworykin, often called the father of TV, chemist Ilya Prigogine, noted for his work on dissipative structures and complex systems (1977 Nobel Prize for Chemistry), economists Simon Kuznets (1971 Nobel Prize) and Wassily Leontief (1973 Nobel Prize), physicist Georgiy Gamov (an author of the Big Bang theory), engineer Alexander M. Poniatoff, who created the world's first rotary head recorder and social scientist Pitirim Sorokin who played an important role in development of sociology in the US.