The fact that the focus has always been on this component is no accident. The invention of the first winding technology and the continuous development of new and optimized winding technologies is part of FAULHABER's DNA. The skew-wound wiring of the very first winding is also the symbol used in the corporate logo. Winding technology is therefore not just a design detail but the heart and identity of FAULHABER drive technology.
Lookback: Origins of the FAULHABER Winding
In the 1950s, Dr. Fritz Faulhaber was working meticulously on a project at his precision mechanics workshop. He was developing an innovative camera for the prestigious customer Voigtländer. Dr. Faulhaber was toying with the idea of using an electric motor to transport the film – he decided to pursue his idea and find a solution.
The main problem is that most DC electric motors have a winding around T-shaped teeth of the rotor, which gives these motors the name "T-armature motor". The teeth cause the rotor to assume preferred positions relative to the permanent magnet and then exhibit a so-called cogging torque. At a low supply voltage, it may be the case that the motor does not start to move at all or, during operation, comes to a standstill. Even at a voltage sufficient for a motion impulse, the cogging torque causes a non-uniform rotation and prevents a constant angular speed.
Dr. Faulhaber finally realized that the iron core must go. He decided to manufacture a self-supporting basket winding or bell-type armature winding, without the disruptive winding overhang or space-consuming coil support. In 1958, he made a breakthrough and submitted the patent application for an "electric motor with an ironless coil with self-supporting skew winding". The patent was granted in 1965 and a new motor winding conquered the market.
Well wound is half the battle
The self-supporting, diagonal rotor winding has an extremely low inertia, which enables particularly fast response times and high dynamics. The absence of cogging torques and iron losses as well as extremely precise controllability increased the efficiency and perfected the invention. The path to success took its course.
Further development of the winding technology continues unabated and opens up new possibilities, also in the miniaturization of drive systems. An impressive example of this is the tiny winding used in an extremely delicate motor: With an outer diameter of just 1.9 mm, the winding for the motor measures just 1.4 mm. The diameter of the copper wires used also sets new standards: Today, extremely fine wires – thinner than a human hair – can be manufactured with extremely high precision, which, despite the minute dimensions, makes high-performance and reliable windings possible.
The years following development of the first bell-type armature coil saw the continuous addition of linear, pin, segment and slotted copper windings to the technological portfolio. This variety is not an end in itself: drive solutions are increasingly required for applications where the available installation space is constantly shrinking but at the same time the need for greater performance, dynamics and efficiency is growing. Even greater focus is therefore placed on winding technology – as a crucial lever for optimization and targeted new developments.
An example of this are the brushless BXT flat motors with external rotor technology, whose high-performance inner workings are based on a precise electromagnetic design of the stator and rotor. With 14 powerful NdFeB single magnets on the rotor and 12 teeth on the stator, proven concepts meet an innovative winding technology. An extraordinarily high copper filling factor in the winding ensures maximum power density, while space requirements are reduced to a minimum thanks to optimum wiring.
With the BP4 brushless motors too, the winding is key to performance. The segment winding with overlapping, nested, individually wound segments means that an especially large amount of copper can be accommodated in the coil. The result is a high winding symmetry with minimum losses – and therefore a correspondingly high degree of efficiency.
The central role that the winding also plays with respect to stability and reliability is demonstrated by the example of BX4 motors: Here, the winding is overmolded to retain its shape permanently and also to guarantee maximum stability under demanding operating conditions.
The know-how gathered over many decades and the continuously optimized range of winding technologies have established themselves on the market and form the basis for the drive technologies that FAULHABER uses to shape the trends of today and the future. As was recently the case with the new series of SXR/GXR motors, which have a hexagonal winding – including optimized processes and high performance.
The Performance Secret on the Inside
Armin Mannsdörfer, Team Leader for Winding Technology, and Dr. Roland Keller, Team Leader for Electrical Design, have worked at FAULHABER for many years, have supervised numerous projects and have helped optimize the copper heart of the motors. The two experts provide an exclusive insight into the development of the winding for the SXR/GXR DC-motors and explain what specific features were conceived and how the innovative winding affects the performance and versatility of this motor family.
Armin Mannsdörfer
What role does the winding geometry play with regard to parameters such as torque, speed behavior and thermal management?
The self-supporting winding enables cogging-free and efficient operation. Although cooling of the winding is challenging due to the design, the reinforcement used means that the winding can cope well with the prevailing temperatures, even under heavy loads and at high speeds.
What challenges had to be tackled during development and industrialization of the hexagonal winding?
The wide variety of different winding designs, coupled with the relatively thick-walled winding, places high demands on the processing technology. For this purpose, new technologies were developed and implemented for which patents have been registered. What is new is the design of the winding with a high copper filling factor and a relatively high wall thickness. The processing technology also has to be designed in such a way that a wide variety of motor sizes and voltage types is possible. Although the technology that we have developed for this is more complex than the previously customary technologies, it allows the high-performance windings to be manufactured in a wide range of variants and also achieves a high level of precision with respect to the winding characteristics.
Dr. Roland Keller
What makes the new hexagonal winding of the SXR and GXR motors special from a technical viewpoint?
The straight interior increases the torque constant. If dimensioned correctly, this improves the characteristic curve gradient, which in turn means improved efficiency for the user. At the same time, improved efficiency results in an increase in the permissible continuous torque of a motor.
In what applications do customers benefit particularly strongly from this new winding technology?
As the SXR/GXR motors have a better characteristic curve gradient compared to other motors available on the market and, therefore, enable a higher torque, the use of SXR/GXR motors can save volume and/or mass in the application. Even if the possible continuous torque is not fully utilized, there are still benefits for the user. If two motors have the same friction, then the motor with the better characteristic curve gradient will deliver the better efficiency. A fact which is particularly valued by experts in the field.