A direct-drive mechanism is a

mechanism Mechanism may refer to: * Mechanism (engineering), rigid bodies connected by joints in order to accomplish a desired force and/or motion transmission *Mechanism (biology), explaining how a feature is created *Mechanism (philosophy), a theory that ...

design where the

force In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a p ...

torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...

from a

prime mover Prime mover may refer to: Philosophy *Unmoved mover, a concept in Aristotle's writings Engineering * Prime mover (engine), motor, a machine that converts various other forms of energy (chemical, electrical, fluid pressure/flow, etc) into energy ...

is transmitted directly to the effector device (such as the

drive wheel A drive wheel is a wheel of a motor vehicle that transmits force, transforming torque into tractive force from the tires to the road, causing the vehicle to move. The powertrain delivers enough torque to the wheel to overcome stationary for ...

s of a

vehicle A vehicle (from la, vehiculum) is a machine that transports people or cargo. Vehicles include wagons, bicycles, motor vehicles (motorcycles, cars, trucks, buses, mobility scooters for disabled people), railed vehicles (trains, trams), wa ...

) without involving any intermediate

coupling A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. The primary purpose of couplings is to join two pieces of rotating equipment while permitting some degree of misalignment or end mov ...

s such as a

gear train A gear train is a mechanical system formed by mounting gears on a frame so the teeth of the gears engage. Gear teeth are designed to ensure the pitch circles of engaging gears roll on each other without slipping, providing a smooth transmission ...

or a

belt Belt may refer to: Apparel * Belt (clothing), a leather or fabric band worn around the waist * Championship belt, a type of trophy used primarily in combat sports * Colored belts, such as a black belt or red belt, worn by martial arts practit ...

.Asada, H., & Kanade, T. (1983)
Design of direct-drive mechanical arms
' in ''Journal of Vibration, Acoustics, Stress, and Reliability in Design'', Volume 105, Issue 3, pp.312-316

History

In the late 19th century and early 20th century, some of the earliest locomotives and cars used direct drive transmissions at higher speeds. Direct-drive mechanisms for industrial arms began to be possible in the 1980s, with the use of rare-earth magnetic materials. The first direct-drive arm was built in 1981 at

Carnegie Mellon University Carnegie Mellon University (CMU) is a private research university in Pittsburgh, Pennsylvania. One of its predecessors was established in 1900 by Andrew Carnegie as the Carnegie Technical Schools; it became the Carnegie Institute of Technology ...

. Today the most commonly used magnets are

neodymium magnet A hard_disk_drive.html"_;"title="Nickel-plated_neodymium_magnet_on_a_bracket_from_a_hard_disk_drive">Nickel-plated_neodymium_magnet_on_a_bracket_from_a_hard_disk_drive_ file:Nd-magnet.jpg.html" ;"title="hard_disk_drive_.html" ;"title="hard_disk_d ...

Design

Direct-drive systems are characterized by smooth torque transmission, and nearly-zero

backlash Backlash may refer to: Literature * '' Backlash: The Undeclared War Against American Women'', a 1991 book by Susan Faludi * ''Backlash'' (Star Wars novel), a 2010 novel by Aaron Allston * Backlash (Marc Slayton), comic book character * ''Backla ...

.Bruno Siciliano, Oussama Khatib (Eds., 2008)
Springer Handbook of Robotics
', p.80Robotics Technology Abstracts
Volume 4, Cranfield Press, 1985, p.362, quote: "direct drive. The direct coupling of motors eliminates backlash completely" The main benefits of a direct-drive system are increased efficiency (due to reduced power losses from the drivetrain components) and being a simpler design with fewer moving parts. Major benefits also include the ability to deliver high torque over a wide range of speeds, fast response, precise positioning, and low

inertia Inertia is the idea that an object will continue its current motion until some force causes its speed or direction to change. The term is properly understood as shorthand for "the principle of inertia" as described by Newton in his first law ...

. The main drawback is that a special type of electric motor is often needed to provide high torque outputs at low

rpm Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines. Standards ISO 80000-3:2019 defines a unit of rotation as the dimensionl ...

. Compared with a multi-speed transmission, the motor is usually operating in its optimal

power band The power band of an internal combustion engine or electric motor is the range of operating speeds under which the engine or motor is able to output the most power, that is, the maximum energy per unit of time. This usually means that maximum a ...

for a smaller range of output speeds for the system (e.g., road speeds in the case of a motor vehicle). Direct-drive mechanisms also need a more precise control mechanism. High-speed motors with speed reduction have relatively high inertia, which helps smooth the output motion. Most motors exhibit positional

torque ripple Torque ripple is an effect seen in many electric motor designs, referring to a periodic increase or decrease in output torque as the motor shaft rotates. It is measured as the difference in maximum and minimum torque over one complete revolution, ge ...

known as

cogging torque Cogging torque of electrical motors is the torque due to the interaction between the permanent magnets of the rotor and the stator slots of a permanent magnet machine. It is also known as ''detent'' or ''no-current torque''. This torque is position ...

. In high-speed motors, this effect is usually negligible, as the frequency at which it occurs is too high to significantly affect system performance; ''direct-drive'' units will suffer more from this phenomenon unless additional inertia is added (i.e. by a

flywheel A flywheel is a mechanical device which uses the conservation of angular momentum to store rotational energy; a form of kinetic energy proportional to the product of its moment of inertia and the square of its rotational speed. In particular, ass ...

) or the system uses feedback to actively counter the effect.

Applications

Direct-drive mechanisms are used in applications ranging from low speed operation (such as

phonograph A phonograph, in its later forms also called a gramophone (as a trademark since 1887, as a generic name in the UK since 1910) or since the 1940s called a record player, or more recently a turntable, is a device for the mechanical and analogu ...

telescope mount A telescope mount is a mechanical structure which supports a telescope. Telescope mounts are designed to support the mass of the telescope and allow for accurate pointing of the instrument. Many sorts of mounts have been developed over the year ...

s and

ski lift A ski lift is a mechanism for transporting skiers up a hill. Ski lifts are typically a paid service at ski resorts. The first ski lift was built in 1908 by German Robert Winterhalder in Schollach/Eisenbach, Hochschwarzwald. Types * Aerial l ...

s, video game racing wheels and

gearless wind turbine Wind turbine design is the process of defining the form and configuration of a wind turbine to extract energy from the wind. An installation consists of the systems needed to capture the wind's energy, point the turbine into the wind, convert ...

s) to high speeds (such as

fans Fan commonly refers to: * Fan (machine), a machine for producing airflow, often used for cooling ** Hand fan, an implement held and waved by hand to move air for cooling * Fan (person), short for fanatic; an enthusiast or supporter, especially wit ...

, computer hard drives, VCR heads,

sewing machine A sewing machine is a machine used to sew fabric and materials together with thread. Sewing machines were invented during the first Industrial Revolution to decrease the amount of manual sewing work performed in clothing companies. Since the inv ...

s, CNC machines and

washing machine A washing machine (laundry machine, clothes washer, washer, or simply wash) is a home appliance used to wash laundry. The term is mostly applied to machines that use water as opposed to dry cleaning (which uses alternative cleaning fluids and ...

s.) Some electric railway locomotives have used direct-drive mechanisms, such as the 1919

Milwaukee Road class EP-2 The Milwaukee Road's class EP-2 comprised five electric locomotives built by General Electric in 1919. They were often known as Bipolars, which referred to the bipolar electric motors they used. Among the most distinctive and powerful electric l ...

and the 2007 East Japan Railway Company E331. Several cars from the late 19th century used direct-drive

wheel hub motor The wheel hub motor (also called wheel motor, wheel hub drive, hub motor or in-wheel motor) is an electric motor that is incorporated into the hub of a wheel and drives it directly. History * First wheel motor concept: Wellington Adams of ...

s, as did some concept cars in the early 2000s; however, most modern

electric car An electric car, battery electric car, or all-electric car is an automobile that is propelled by one or more electric motors, using only energy stored in batteries. Compared to internal combustion engine (ICE) vehicles, electric cars are quie ...

s use inboard motor(s), where drive is transferred to the wheels, via the

axle An axle or axletree is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In the former case, bearing ...

s. Some automobile manufacturers have managed to create their own unique direct-drive transmissions, such as the one

Christian von Koenigsegg Christian Erland Harald von Koenigsegg (born July 2, 1972)known professionally as Christian von Koenigsegg is an automotive engineer and entrepreneur, and is the founder and CEO of the Swedish high-performance automobile manufacturer Koenigsegg ...

invented for the

Koenigsegg Regera The Koenigsegg Regera is a limited production, plug-in hybrid grand touring sports car manufactured by Swedish automotive manufacturer Koenigsegg. It was unveiled at the March 2015 Geneva Motor Show. The name Regera is a Swedish verb, meaning " ...

References

{{Reflist Mechanisms (engineering) Gearless electric drive

History

Design

Applications

See also

References