Direct-drive mechanism explained

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, 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

Notes and References

  1. 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. Web site: Auto Repair - Maintenance, Troubleshooting and Car Repair Estimates.
  3. Web site: Why the Porsche Taycan EV's Two-Speed Transmission Is a Big Deal.
  4. Web site: What is a Direct Drive Motor Electric Torque Machines. dead . https://web.archive.org/web/20181110194447/http://etmpower.com/learn-more/what-is-a-direct-drive-motor . 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. Web site: What is a Strong Magnet?. The Magnetic Matters Blog. Adams Magnetic Products. October 5, 2012. October 12, 2012. March 26, 2016. https://web.archive.org/web/20160326224820/http://www.adamsmagnetic.com/blogs/2012/what-is-a-strong-magnet/. dead.
  9. Bruno Siciliano, Oussama Khatib (Eds., 2008) Springer Handbook of Robotics, p.80
  10. https://books.google.com/books?id=0KyZAAAAIAAJ&q=Backlash Robotics Technology Abstracts
  11. [Armed Services Board of Contract Appeals|United States Armed Services Board of Contract Appeals]
  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. Web site: Fanatec Release Details On Their(sic) Direct Drive Wheel - Inside Sim Racing. 4 June 2017.
  15. Web site: Patel. Prachi. GE Grabs Gearless Wind Turbines. Technology Review (MIT). 7 April 2011. 31 January 2012. https://web.archive.org/web/20120131060053/http://www.technologyreview.com/energy/23517/?a=f. dead.
  16. Web site: Dvorak. Paul. Direct drive turbine needs no gearbox. Windpower Engineering. 7 April 2011. 21 February 2017. https://web.archive.org/web/20170221010623/http://www.windpowerengineering.com/design/mechanical/gearboxes/direct-drive-turbine-needs-no-gearbox/. dead.
  17. Web site: In-wheel motor . Nissan Motor Corporation . 9 July 2021 . live. https://web.archive.org/web/20150404003952/http://www.nissan-global.com:80/EN/TECHNOLOGY/OVERVIEW/in_wheel_motor.html . 2015-04-04 .
  18. Web site: How Do All-Electric Cars Work? . Alternative Fuels Data Center . U.S. Department of Energy . 9 July 2021 . live. https://web.archive.org/web/20160930060719/http://www.afdc.energy.gov:80/vehicles/how-do-all-electric-cars-work . 2016-09-30 .
  19. Web site: 2015-03-17. Koenigsegg creates a new breed of hyper-hybrid with 1,500-hp, transmission-less Regera. live. 3 May 2021. New Atlas. en-US. https://web.archive.org/web/20160812181132/http://newatlas.com:80/koenigsegg-regera-geneva/36376/ . 2016-08-12 .

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