Cogging-free use: DC motors from FAULHABER

DC is an acronym for "direct current." A DC motor converts direct current into mechanical energy. Its most important components are a moving rotor, a fixed stator, and a commutator, which is a current or pole inverter that directs the current into the rotor with a constantly changing direction of flow. In conventional DC motors, the rotor consists of a coil wound around an iron core (armature) which is surrounded on the outside by U-shaped stator magnets. In the DC motors from FAULHABER, it is the other way around.

How are FAULHABER DC motors designed?

In the DC motors from FAULHABER, the permanent magnet stator is cylindrical and is located on the inside, while the rotor rotates around it on the outside.

The rotor consists of an ironless, self-supporting copper coil with skew winding. This technology was developed by Dr. Fritz Faulhaber Sr. and patented in 1958. It is at the heart of what DC motors from FAULHABER are all about. The only exception are the flat DC -micromotors of the SR-Flat series: Here, the rotor and stator are arranged in a disc shape to save length.

The total weight of the motor is very low thanks to the ironless, self-supporting copper coil. In addition, this structure ensures a minimum moment of inertia and cogging-free, high-precision running. Thanks to these features, DC motors from FAULHABER have particularly high dynamics and high power density.

The stator of a DC motor is a permanent magnet. Direct current is conducted into the rotor. This creates magnetic fields that are repelled or attracted by the magnetic poles of the stator. This force creates the movement of the DC motor. The commutator constantly reverses the flow direction of the current and thus the polarity of the magnetic fields. In this way, a continuous rotation can result from the single attraction and repelling of the poles. The current is transmitted to the rotor by a sliding contact, the so-called brushes.

This current transfer is called commutation. FAULHABER offers two variants:

• Precious metal commutation has low current density and low contact resistance. This variant is particularly well-suited for low-power, battery-powered, and low-start-up voltage applications.
• With graphite commutation, the spring-loaded brushes are made of a combination of graphite with copper or silver. They have a large contact surface and achieve a strong contact force for optimal power transmission to the winding, even when shocks or vibrations occur.

The basic parameters are

• Rated current and rated voltage
• Speed and torque
• Size (max. length and diameter)

Among the numerous product variants from FAULHABER, there is almost always a drive that offers the optimal solution for your requirements. With an additional gearhead, for example, the speed range can be significantly expanded or the torque adjusted. FAULHABER offers a wide portfolio of gearheads that are perfectly matched to the DC motors.

The location and type of mounting points as well as the shaft diameter can also play an important role in the selection. It also depends on the external conditions of use. In the case of adverse environmental influences such as moisture, dust, negative pressure or extreme temperatures, a certain degree of protection, suitability for vacuum, or a particularly large temperature range may be required.

The available accessories may also factor in. FAULHABER offers the industry's largest selection of customized combination options for its DC motors: In addition to our precision gearheads (planetary gearheads, spur gearheads and zero backlash spur gearheads), our portfolio also includes high-resolution encoders (incremental and absolute encoders) as well as powerful controls (Speed Controller, Motion Controller). Our Drive Calculator enables you to quickly find the DC motor that best matches your requirements. We also offer our customers the bespoke manufacture of drives that are configured for a specific application.

Our tutorial Motor Calculations for Coreless Brush DC Motors explains how the central drive parameters are calculated for an application. It helps you to select the right DC motor for the application or a prototype. The tutorial summarizes the most important methods, formulas, and calculation details with which the power output, the speed-torque characteristic curve, and the current and efficiency characteristic curves can be determined.

Brushed DC motors have design-related benefits that can play an important role when selecting a motor.

• Simple control, easy integration: With brushless motors, the rotating field has to change constantly, which requires a feedback loop and some effort when controlling it. A brushed DC motor, on the other hand, only requires a DC voltage connection. This means it can be easily integrated into any control.
   
• Low moment of inertia, high dynamics: A self-supporting ironless copper winding with a very low mass and correspondingly minimal moment of inertia rotates in the DC motors from FAULHABER. This gives the motor a high level of dynamics: It delivers high performance even at a very low starting voltage and can also work at low speeds. This is especially important when it is operated by battery power. At the same time, it can perform very fast speed changes. Due to the low moment of inertia, however, its overload capacity is limited.
   
• Simple structure, cost-effective solutions: Thanks to the simple design, brushed DC motors require few electronics and – depending on the variant – even work with simple components. This means it enables very cost-effective solutions.

In comparison, brushless DC motors require significantly more complex electronics. This also means they are more expensive and require more effort during integration. Because the coil is fixed and the magnets move, the moment of inertia is larger in this type of motor. It requires a higher starting voltage, but at the same time it can withstand more overload. Brushless DC motors play to their strengths particularly in frequent overload conditions and in applications with continuous operation where a maximum service life is required: they don't need a brush, which is subject to wear. They are also available as flat motors with a very short overall length.