direct-drive mechanism#Other uses
{{Short description|Transmission of torque from motor to output without gearing}}
{{Refimprove|date=January 2010}}
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.Asada, H., & Kanade, T. (1983) [https://scholar.google.com/scholar?cluster=490826303723520066 Design of direct-drive mechanical arms] in Journal of Vibration, Acoustics, Stress, and Reliability in Design, Volume 105, Issue 3, pp.312-316{{cite web |url=https://www.autoblog.com/2015/11/30/what-is-direct-drive-gear/ |title = Auto Repair - Maintenance, Troubleshooting and Car Repair Estimates}}{{cite web |url=https://www.caranddriver.com/news/a28903274/porsche-taycan-transmission/ |title = Why the Porsche Taycan EV's Two-Speed Transmission Is a Big Deal}}{{cite web |url=https://etmpower.com/learn-more/what-is-a-direct-drive-motor/#:~:text=Direct%20Drive%20motors%20are%20simply,to%20achieve%20the%20necessary%20torque. |url-status=dead |archive-url=https://web.archive.org/web/20181110194447/http://etmpower.com/learn-more/what-is-a-direct-drive-motor |archive-date=2018-11-10 |title=What is a Direct Drive Motor {{!}} Electric Torque Machines}}
History
In the late 19th century and early 20th century, some of the earliest locomotives and cars used direct drive transmissions at higher speeds.P. Ransome-Wallis (2001) [https://books.google.com/books?id=GVgiRfFBiTgC&pg=PA461 Illustrated Encyclopedia of World Railway Locomotives], p.63Roy V. Wright (ed.) (1938) [https://books.google.com/books?id=5CVSAQAAIAAJ&pg=PA973 Locomotive Cyclopedia of American Practice], section 16 "Diesel locomotives", 10th edition, Association of American Railroads - Mechanical Division, p.973 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.Baichun Zhang, Marco Ceccarelli (Eds.) [https://books.google.com/books?id=HaZ-DwAAQBAJ&pg=PA292 Explorations in the History and Heritage of Machines and Mechanisms], p.292
Today the most commonly used magnets are neodymium magnets.{{cite web| title = What is a Strong Magnet?| website = The Magnetic Matters Blog| publisher = Adams Magnetic Products| date = October 5, 2012| url = http://www.adamsmagnetic.com/blogs/2012/what-is-a-strong-magnet/| access-date = October 12, 2012| archive-date = March 26, 2016| archive-url = https://web.archive.org/web/20160326224820/http://www.adamsmagnetic.com/blogs/2012/what-is-a-strong-magnet/| url-status = dead}}
Design
Direct-drive systems are characterized by smooth torque transmission, and nearly-zero backlash.Bruno Siciliano, Oussama Khatib (Eds., 2008) [https://books.google.com/books?id=Xpgi5gSuBxsC&pg=PA80 Springer Handbook of Robotics], p.80[https://books.google.com/books?id=0KyZAAAAIAAJ&q=Backlash Robotics Technology Abstracts], Volume 4, Cranfield Press, 1985, p.362, quote: "direct drive. The direct coupling of motors eliminates backlash completely"United States Armed Services Board of Contract Appeals (1966) [https://books.google.com/books?id=Uqi6cvLDBV4C&pg=PA764 Board of Contract Appeals Decisions], Volume 66, Issue 1, p.764, published by Commerce Clearing House
The main{{cn|date=September 2021}} 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.Uday Shanker Dixit, Manjuri Hazarika, J. Paulo Davim (2016) [https://books.google.com/books?id=3KDVDAAAQBAJ&pg=PA160 A Brief History of Mechanical Engineering], ch.7 "History of Mechatronics", pp.160-161K. T. Chau [https://books.google.com/books?id=O3FXCQAAQBAJ&pg=PA227 Electric Vehicle Machines and Drives: Design, Analysis and Application], ch.8 "Vernier Permanent Magnet Motor Drives", p.227
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){{cite web|url=http://www.isrtv.com/fanatec/fanatec-release-details-on-thier-direct-drive-wheel/|title=Fanatec Release Details On Their(sic) Direct Drive Wheel - Inside Sim Racing|date=4 June 2017}}{{cite web|last=Patel|first=Prachi|title=GE Grabs Gearless Wind Turbines|url=http://www.technologyreview.com/energy/23517/?a=f|publisher=Technology Review (MIT)|access-date=7 April 2011|archive-date=31 January 2012|archive-url=https://web.archive.org/web/20120131060053/http://www.technologyreview.com/energy/23517/?a=f|url-status=dead}}{{cite web|last=Dvorak|first=Paul|title=Direct drive turbine needs no gearbox|url=http://www.windpowerengineering.com/design/mechanical/gearboxes/direct-drive-turbine-needs-no-gearbox/|publisher=Windpower Engineering|access-date=7 April 2011|archive-date=21 February 2017|archive-url=https://web.archive.org/web/20170221010623/http://www.windpowerengineering.com/design/mechanical/gearboxes/direct-drive-turbine-needs-no-gearbox/|url-status=dead}} 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.{{cite web |url=https://www.nissan-global.com/EN/TECHNOLOGY/OVERVIEW/in_wheel_motor.html |title=In-wheel motor |publisher=Nissan Motor Corporation |access-date=9 July 2021 |url-status=live|archive-url=https://web.archive.org/web/20150404003952/http://www.nissan-global.com:80/EN/TECHNOLOGY/OVERVIEW/in_wheel_motor.html |archive-date=2015-04-04 }}{{cite web |url=https://afdc.energy.gov/vehicles/how-do-all-electric-cars-work |title=How Do All-Electric Cars Work? |work=Alternative Fuels Data Center |publisher=U.S. Department of Energy |access-date=9 July 2021 |url-status=live|archive-url=https://web.archive.org/web/20160930060719/http://www.afdc.energy.gov:80/vehicles/how-do-all-electric-cars-work |archive-date=2016-09-30 }}
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.{{Cite web|date=2015-03-17|title=Koenigsegg creates a new breed of hyper-hybrid with 1,500-hp, transmission-less Regera|url=https://newatlas.com/koenigsegg-regera-geneva/36376/|url-status=live|access-date=3 May 2021|website=New Atlas|language=en-US|archive-url=https://web.archive.org/web/20160812181132/http://newatlas.com:80/koenigsegg-regera-geneva/36376/ |archive-date=2016-08-12 }}