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Direct drive mechanisms can be categorized into groups
(A) Torque motor mechanisms. The output shaft is driven either by brush torque motor or brushless torque motor. The brushless torque motor requires commutation. Battery driven devices such as cordless hand drills are generally used brush torque motors.
The major alternative to the direct-drive mechanism is the geared stepper motor mechanism driven by current pulses.
- Increased efficiency: The power is not wasted in friction (from the belt, chain, etc., and especially, gearboxes.)
- Reduced noise: Being a simpler device, a direct-drive mechanism has fewer parts which could vibrate, and the overall noise emission of the system is usually lower.
- Longer lifetime: Having fewer moving parts also means do not have fewer parts that are prone to failure. Failures in other systems are usually produced by aging of the component (such as a stretched belt), or stress.
- High torque at low rpm.
- Faster and precise positioning. High torque and low inertia allow faster positioning times on permanent magnet synchronous servo drives. The feedback sensor directly on the rotary part allows precise angular position sensing.
- Drive stiffness. Mechanical backlash, hysteresis, and elasticity are removed avoiding the use of gearbox or ball screw mechanisms.
The main disadvantage of the system is that it needs a special electric motor. Usually, motors are built to achieve maximum torque at high rotational speeds, usually 1500 or 3000 rpm. While this is useful for many applications (such as an electric fan), other mechanisms need relatively high torque at very low speeds, such as a phonograph turntable, which needs a constant (and very precise) 331⁄3 rpm or 45 rpm.
The slow motor also needs to be physically larger than its faster counterpart. For example, in a belt-coupled turntable, the motor diameter is about 25 mm (1 in). On a direct-drive turntable, the motor is about 100 mm (4 in).
Also, direct-drive mechanisms 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 known as cogging torque. 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) or the system uses feedback to actively counter the effect.
Direct-drive mechanisms are present in several products:
- Fans: Imprecise, depending on the fan, between 1000 and 21000 rpm.
- Hard drives: Very precise, 5400, 7200, 10000, 15000 rpm and others.
- VCR heads: Very precise, 1800 rpm (NTSC) or 1500 rpm (PAL).
- Sewing machines: 3000 rpm to 5000 rpm depending on machine type.
- Turn tables: CNC machines with fast and precise turning tables
- Washing machines: up to 1600 rpm spin speeds
Medium-speed or variable-speed
- Floppy disk drives
- CD drives: the CD is directly coupled to the rotor; 250 to 500 rpm for audio, higher speeds in portable and computer drives.
Very low rotational speeds
- Phonograph turntables: Very precise, 78, 331⁄3 and 45 rpm.
- Telescope mount: Very precise, e.g. 1 revolution in 24 h.
- Ski lift drive: up to 30 rpm depending upon line speed.
- Washing machines: Various manufacturers, including Arçelik, Fisher & Paykel, LG, Samsung, Whirlpool and Toshiba have released washing machines where the drum is driven directly by the motor, replacing the usual noisy and less efficient belt or gearbox-driven system.
- Railway vehicles: The Milwaukee Road class EP-2 electric locomotives introduced in 1919 had the driving wheels mounted directly to the traction motor shafts. East Japan Railway Company (JR East) built an experimental E993 series electric multiple-unit (EMU) called the "AC Train" in January 2002 to test the feasibility of direct-drive motors on commuter trains. The technology was later incorporated in the E331 series EMU which entered service on the Keiyō Line in 2007.
- Road vehicles: Wheel hub motors date to the late 19th century, and used in modern (the 2000s) electric vehicle concepts
- Wind turbines (see Gearless wind turbines): Various companies have developed direct drive generators for wind turbines, which are designed to improve efficiency and decrease maintenance costs.
- Cycles: Some cycle types e.g. unicycles, penny-farthings, and children's tricycles.
- Racing wheel controllers for video games
- Patel, Prachi. "GE Grabs Gearless Wind Turbines". Technology Review (MIT). Retrieved 7 April 2011.
- Dvorak, Paul. "Direct drive turbine needs no gearbox". Windpower Engineering. Retrieved 7 April 2011.
- "Fanatec Release Details On Their(sic) Direct Drive Wheel - Inside Sim Racing". 4 June 2017.