Torque motors are motors with a particularly high torque. This means that an additional gearbox can often be dispensed with. This is why torque motors are also referred to as direct drives. These electric motors are usually relatively short compared to high speed motors. On the other hand, high torque motors usually have a large diameter. The large diameter of the rotor ensures a high torque in the lower speed range. High speed motors, on the other hand, usually have a small diameter. And are usually relatively long. The torque of high speed motors is much smaller in comparison, but they achieve higher speeds. In most cases, the torque drops much faster with high torque motors. However, this depends heavily on the type of electric motor that is used as a high torque motor. In the YouTube video below, all the main high torque motor types are presented.
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AC motors and BLDC motors without brushes are primarily used for torque motors. These are often also referred to as brushless DC motors. There are two motor designs of high torque electric motors that are primarily used. These are axial flux motors and radial flux motors. Radial flux motors can be further subdivided into two different types. These are motors with internal rotors and external rotors. External rotors are primarily used for high torque radial flux motors. Transverse flux motors can also generate high torques. However, they are very rarely used in industry. Permanent magnets are generally used for all these types of electric motor. This is because permanent magnets can get a higher torque out of the motor with the same phase current. However, it is of course also possible to build a high torque motor without permanent magnets. For example, as a reluctance motor with an external rotor. In the YouTube video below you can watch an animation of a high torque reluctance motor.
So what makes a high torque motor so special? The secret of high torque motors is primarily the large diameter. This is the main reason why axial flux motors and external rotor motors are often used. Because these types of electric motors are well suited for short motors with a large diameter. It is not the outer diameter of the rotor that is important, but the diameter of the central air gap. This is where the mechanical forces between the rotor and stator are generated by the magnetic flux. The larger the diameter where these forces arise, the greater the resulting torque. Of course, it is also possible to build high torque motors with a small diameter, but this is not so easy. Another important characteristic of high torque motors is the high number of permanent magnets. However, the combination of stator and rotor poles should always be a good match. Another important point is the strength and thickness of the permanent magnets. The stronger and thicker the permanent magnets are made, the bigger the torque will be. Of course, the torque can only ever be increased within certain limits. And the maximum speed that the electric motor can achieve also decreases as a result. This is because the back EMF also increases when stronger magnets are used. There are of course other ways to increase the torque. For example, by using a smaller air gap or a higher phase current from the inverter.
Due to the high torques of high torque electric motors, an additional gearbox is no longer necessary in many cases. This eliminates the losses of a gearbox and increases the overall efficiency of the electric drive. This is because it only consists of the high torque motor and the inverter or power electronics. This is a great advantage for electric boats and electric airplanes, for example. But it is also good for electric motorcycles and mobile robots. However, high torque motors without a gearbox are usually larger than electric motors with a gearbox. This is because the high torque motor usually has a lower speed than a motor with a gearbox. Due to the lower speed, high torque motors also usually have a lower power density. However, the overall size of high torque motors is usually comparable with drives that have a gearbox. However, this is of course also heavily dependent on the type of gearbox that is used.
Thanks to their excellent dynamics, high torque motors are also used in production machines, robots and machine tools. In order to accelerate the masses of machines with high torques more quickly. By eliminating the need for a gearbox in a machine tool, a high torque motor not only allows workpieces to be machined faster, but also more precisely. In production machines, maintenance costs can be reduced by eliminating gearboxes and using high torque motors. This is because it only consists of the high torque motor and the inverter or power electronics.
Frameless refers to a motor without a frame, housing, bearing or feedback system. Our Framless High Torque Motors Series are designed to be built in the integral part of a system. With its outrunner and frameless design, size and weight are decreased making the motors easy to integrate and use in various applications. In addition, because of the high specific torque density, frameless torque motors are very suitable for small building volumes.
There are two types of direct drive frameless torque motors: the outrunner and the inrunner torque motors. For an inrunner motor, the rotor is located on the inside of the stator. In case of the outrunner motor, the rotor is located on the outside of the stator. Advantages of these motors are:
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Magnetic Innovations specialises in both the outrunner and the inrunner typologies. Each motor typology provides specific advantages, but they function similarly in their core operation.
The stator is the static part of the torque motor, which contains the lam stack and copper wire. Moreover, the lam stack contains “lam stack teeth” or “stator teeth”. On each of these teeth copper windings are wound. When three phase AC current is supplied to the copper windings, the stator turns into an array of electromagnets. As a result, an alternating rotating magnetic field is created around the stator, as shown in the video to the right. The orange and blue areas depict the south and north part, respectively. Further, the copper windings on the stator can be configured in different ways to create different performance parameters that can be important for various applications.
The rotor is the moving or rotating part of the torque motor, which contains the permanent magnets. The permanent magnets are placed on the rotor in a north south north south pattern. The blue and orange areas depict the north and south part, respectively. This is shown in the video to the right. Consequently, the permanent magnetic field of the rotor will interact with the alternating magnetic field of the rotor. Further, between the stator and the rotor the magnetic air gap is located.
In case of an outrunner torque motor, the rotor is put around the stator. As a result, the magnetic field of the stator starts to interact with the permanent magnet field of the rotor. Consequently, the permanent magnetic field of the rotor will start rotating synchronously with the stator magnetic field and torque (N) is created. This is shown in the video to the right.
The torque of the direct drive torque motor is proportional to the current in the stator. In addition, the required voltage is proportional to the speed.
By adjusting the number of windings and / or winding configuration, the ratio between the voltage and current demand can be adjusted. This makes the motor usable for various application areas, such as semicon, robotics, food and packaging.
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