A direct-drive mechanism is a mechanism design where the force or torque from a prime mover is transmitted directly to the effector device (such as the drive wheels of a vehicle) without involving any intermediate couplings such as a gear train or a belt.[1][2][3][4]

History

In the late 19th century and early 20th century, some of the earliest locomotives and cars used direct drive transmissions at higher speeds.[5][6] Direct-drive mechanisms for industrial arms began to be possible in the 1980s, with the use of rare-earth magnetic materials.[1] The first direct-drive arm was built in 1981 at Carnegie Mellon University.[7] Today the most commonly used magnets are neodymium magnets.[8]

Design

Direct-drive systems are characterized by smooth torque transmission, and nearly-zero backlash.[9][10][11] 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.[12][13]

The main drawback is that a special type of electric motor is often needed to provide high torque outputs at low rpm. Compared with a multi-speed transmission, the motor is usually operating in its optimal power band 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 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.

Applications

Direct-drive mechanisms are used in applications ranging from low speed operation (such as phonographs, telescope mounts and ski lifts, video game racing wheels and gearless wind turbines)[14][15][16] to high speeds (such as fans, computer hard drives, VCR heads, sewing machines, CNC machines and washing machines.)

Some electric railway locomotives have used direct-drive mechanisms, such as the 1919 Milwaukee Road class EP-2 and the 2007 East Japan Railway Company E331. Several cars from the late 19th century used direct-drive wheel hub motors, as did some concept cars in the early 2000s; however, most modern electric cars use inboard motor(s), where drive is transferred to the wheels, via the axles.[17][18]

Some automobile manufacturers have managed to create their own unique direct-drive transmissions, such as the one Christian von Koenigsegg invented for the Koenigsegg Regera.[19]

See also

References

  1. 1 2 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
  2. ↑ "Auto Repair - Maintenance, Troubleshooting and Car Repair Estimates".
  3. ↑ "Why the Porsche Taycan EV's Two-Speed Transmission Is a Big Deal".
  4. ↑ "What is a Direct Drive Motor | Electric Torque Machines". Archived from the original on 2018-11-10.
  5. ↑ P. Ransome-Wallis (2001) Illustrated Encyclopedia of World Railway Locomotives, p.63
  6. ↑ Roy V. Wright (ed.) (1938) Locomotive Cyclopedia of American Practice, section 16 "Diesel locomotives", 10th edition, Association of American Railroads - Mechanical Division, p.973
  7. ↑ Baichun Zhang, Marco Ceccarelli (Eds.) Explorations in the History and Heritage of Machines and Mechanisms, p.292
  8. ↑ "What is a Strong Magnet?". The Magnetic Matters Blog. Adams Magnetic Products. October 5, 2012. Archived from the original on March 26, 2016. Retrieved October 12, 2012.
  9. ↑ Bruno Siciliano, Oussama Khatib (Eds., 2008) Springer Handbook of Robotics, p.80
  10. ↑ Robotics Technology Abstracts, Volume 4, Cranfield Press, 1985, p.362, quote: "direct drive. The direct coupling of motors eliminates backlash completely"
  11. ↑ United States Armed Services Board of Contract Appeals (1966) Board of Contract Appeals Decisions, Volume 66, Issue 1, p.764, published by Commerce Clearing House
  12. ↑ Uday Shanker Dixit, Manjuri Hazarika, J. Paulo Davim (2016) A Brief History of Mechanical Engineering, ch.7 "History of Mechatronics", pp.160-161
  13. ↑ K. T. Chau Electric Vehicle Machines and Drives: Design, Analysis and Application, ch.8 "Vernier Permanent Magnet Motor Drives", p.227
  14. ↑ "Fanatec Release Details On Their(sic) Direct Drive Wheel - Inside Sim Racing". 4 June 2017.
  15. ↑ Patel, Prachi. "GE Grabs Gearless Wind Turbines". Technology Review (MIT). Archived from the original on 31 January 2012. Retrieved 7 April 2011.
  16. ↑ Dvorak, Paul. "Direct drive turbine needs no gearbox". Windpower Engineering. Retrieved 7 April 2011.
  17. ↑ "In-wheel motor". Nissan Motor Corporation. Archived from the original on 2015-04-04. Retrieved 9 July 2021.
  18. ↑ "How Do All-Electric Cars Work?". Alternative Fuels Data Center. U.S. Department of Energy. Archived from the original on 2016-09-30. Retrieved 9 July 2021.
  19. ↑ "Koenigsegg creates a new breed of hyper-hybrid with 1,500-hp, transmission-less Regera". New Atlas. 2015-03-17. Archived from the original on 2016-08-12. Retrieved 3 May 2021.
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