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Introduction to Electric Motors
Published in Wei Tong, Mechanical Design and Manufacturing of Electric Motors, 2022
According to the motor nominal power, electric motors can be briefly divided into five categories: Micromotors are electric motors with a rated output power of 0.05 hp (<37 W) or less. Micromotors have been used across a wide range of commercial and industrial applications for light duty, especially in microelectronics, computer, and precision instrument industries.Small motors are larger than 0.05 hp but less than 1 hp (37 W–746 W). Their applications focus primarily on power hand tools, appliances, medical devices, small fans, optical devices, electrical cars, precise motion control systems, and other small machinery.Medium motors are considered to be in the range of 1–100 hp (746 W–74.6 kW). The majority of medium motors are used in various industrial applications such as industrial fans, pumps, motion-control systems, machine tools, and vehicles.Large motors occupy the power range of 100–1,000 hp (74.6 kW–746 kW). They are normally designed for use in medium-duty applications as in elevators, large vehicles, industrial blowers/fans, printing machines, package machines, air compressors, and other industrial large machines.Extra-large motors range from 1,000 to 10,000 hp (746 kW–7.46 MW), which are usually used in heavy-duty applications, such as large rolling mills, large machine tools, high-speed trains, skyway elevators, ship propulsion, and mining machinery.Ultra-large motors are considered to be larger than 10,000 hp (>7.46 MW). NASA used a motor that is rated 135,000 hp for a wind tunnel. In addition, the industry’s largest players such as GE, Siemens, TECO-Westinghouse, ABB, and Toshiba have developed their own ultra-large motors.
Electric-field-guided 3D manipulation of liquid metal microfleas
Published in Soft Materials, 2022
Yongxin Wang, Yanbing Kuai, Guangqiang Zhang, Hairui Zhang, Jiawei Cong, Yunli Xu, Lizhi Yi, Min Liu, Yiman Liu
Man-made micromotors have received mounting interest in recent years, owing to their great potential to perform a broad range of complex tasks, such as lithography,[1] targeted therapeutics,[2,3] material assembly,[4] water treatment,[5,6] and biopsy,[7] etc. Controllable manipulation is a basic requirement[8] for the micromotors to fulfill such intended applications. Over past two decades, considerable efforts have been devoted to developing the manipulation mechanisms of micromotors, and various manipulation strategies have been explored.[9–14] Although these methods are quite general in their applicability, it remains a great challenge to control an individual micromotor in three dimensions (3-D) facilely.[15] The difficulty arises primarily from the needs of complex and expensive actuation system for maintaining motors’ out-of-plane motion. In contrast to plane motions, achieving out-of-plane operation could greatly expand capabilities of micromotors, which enables them to carry out tasks that would be impossible in 2-D. However, the steep instrumental demand restricts the 3-D operation only to a few laboratories with sophisticated manipulation apparatus, greatly hindering their widespread use. On the other hand, with improved maneuverability, future micromotors are expected to accomplish tasks in various environments, such as in air, in solvent and polymer environment,[16,17] or on solid surfaces and multiphase interfaces. So far, a variety of micromotors that function in aqueous media have been developed,[18–20] and as mentioned above, various manipulation strategies, be it electrical,[21] optical,[22] magnetic,[23,24] acoustic or chemical,[25–27] have been explored to control them. Due to the great success in aqueous solution, it is easy to assume that these manipulation methods will be naturally applicable in non-liquid environments. However, dominant adhesion in non-liquid environment rules out such notions,[28] especially for the soft micromotors[29,30] with viscous skins. For instance, liquid metals (LM), such as gallium and its alloys,[31–40] are widely used materials in soft micromotors, because they are deformable, stretchable, injectable, and shape-reconfigurable at room-temperature. However, the adhesion force holding a Gallium-based LM microdroplet to a solid surface could easily reach to 10−3 mN ~10 mN,[41,42] which exceeds its gravitational force by factors greater than 103. As a consequence, the Gallium-based LM microdroplets usually intend to be stuck to solid surfaces with great tenacity,[43] much like wet paint, which makes them difficult to handle in non-liquid environments.