Zero cogging BLDC motors

We offer two types of cogging-free motors from our manufacturer partner ThinGap.

TG Series: Ironless for high power density

LSI-Series: Slotless design with back-iron for high torque density

The stator of the TG motors has no iron core ("ironless"). The motor is designed to run at high speeds to provide high power density. Thus, the ironless stator is desirable, as it reduces the back EMF. The back EMF is a voltage generated by any permanent magnet motor which is spinning. The amount of back EMF generated by a permanent magnet motor depends on a parameter called the "back EMF constant". The TG motors are designed to have a low back EMF constant.

The LSI motors have a slotless iron lamination stack which acts as a return path for the stator's magnetic field. The stator winding is bonded to the inside of the iron lamination stack. The lamination stack also provides a good heatsink for the motor at low speeds which makes it very useful for applications like gimbals or optics.

Please keep reading to find out more about each family.

ThinGap’s LSI line targets low speed, high precision applications such as gimbals, optics, and precision robotics.
Highest torque density with high power capability. Low thermal resistance at any speed.

Key features:

• Smooth motion with zero cogging and ultra low torque ripple when paired with a sinusoidal drive
• High peak torque to continuous torque ratio
• Optimized for ultimate torque density
• Stationary lamination stack for typical bore mounting
• 3 phase brushless, sinusoidal waveforms < 1% THD
• Non-saturating facilitates very high peak torque (typically >4:1)
• Exceptionally large clear apertures
• Frame-less kit facilitates deep integration
• Large through hole

We understand that your application has special requirement, so we offer custom motors, or modifications to our standard motors, to meet your specific design requirements to make sure you get the perfect motor for your application. Please contact us to discuss your requirements.

Our manufacturer partner ThinGap’s three-phase, permanent magnet, Brushless DC (BLDC) ring motors are made with proprietary ironless stator technology. The result are motors and generators that are lightweight and high torque which deliver high-power at exceptional rotational smoothness. The “ring” architecture allows for more highly integrated, more compact and lighter system designs.

Unlike slotless motors, only ThinGap delivers “True-Zero™” zero cogging torque.  That’s because ThinGap’s completely ironless stator has no magnetic interaction with the rotor until purposely energized by the controller. This gives them exceptionally precise rotation and unmatched rotational smoothness.

ThinGap Motors offer these advantages:

• High torque-to-weight ratio
• Lightweight and low inertia
• Improved system integration due to our ring architecture
• “True-Zero ™” Zero cogging torque for precision positioning and smooth rotational velocity
• High power density scalable from 50W to 550kW
• Diameters from 40mm to 900 mm

We understand that your application has special requirement, so we offer custom motors, or modifications to our standard motors, to meet your specific design requirements to make sure you get the perfect motor for your application.  Please contact us to discuss your requirements.

The gimbal is a suspension device in which a body is mounted so that it can rotate in all directions in space. In most cases, the gimbal consists of three rings whose axes are offset by 90° and can be rotated in one another. Gimbals are often used in aerospace and stellite communications. For tactical airborne gimbal systems, the cogging-free ThinGap motor sets of the LSI-Series are particularly suitable.

The use of airborne gimbals is widespread in both manned aircraft and unmanned aerial vehicles (UAVs). In addition to their common use in communications systems, they are increasingly being used in law enforcement security systems, search and rescue operations, and in support of Coast Guard severe weather and offshore operations. The use of gimbals has become a critical component of defense agencies' Intelligence, Surveillance and Reconnaissance (ISR) objectives.  These state-of-the-art gimbals, or "balls" as they are often called, are often equipped with advanced sensor payloads such as thermal imagers, high-precision cameras, air-to-ground communications, and lasers for pointing, ranging, and illumination.
Multiaxial gimbals require high-power motors to directly drive their movements and maintain position. As airborne systems, high performance is defined by weight, torque capacity, smooth motion and a desirable form factor. The LSI Series slotless motor kits meet all of these critical requirements.

The patented method of distributing the motor phase coil wires with a very thin cross-section eliminates traditional magnetic stator teeth, resulting in a motor without cogging. Cogging is an undesirable magnetic torque disturbance that occurs in most motors. The main cause of cogging is in the winding patterns of the stator, which must fit into the slots between the traditional iron teeth (or poles), hence the term slotless. Slotless motors eliminate cogging torque and provide smooth motion, which is critical for optical systems for precise aiming, pointing and zooming at long distances, and otherwise for smooth motion for accurate scanning. LSI Series motors also have phase symmetry with less than 1% harmonic distortion, allowing the motors to produce smooth motion.

With very thin wire-wound stators and optimized permanent magnet rotors, LS Series motors can provide the same torque that brushless BLDC motors deliver, combined with zero cogging. Gimbal manufacturers have an inherent need for high torque to move quickly and accurately in azimuth and elevation in most cases, and to stabilize the housing for high applied forces caused by drag from the aircraft's speed and the gimbal's preceding position.

Ultimately, torque motors are the perfect form factor for gimbals with their round shape, direct drive mounting capability, and empty center. Motor kits offer a very large through bore, typically 65% or more of the outer diameter (OD) of the device, due to efficient mechanical design and optimized components. This large through-hole not only saves weight, but also provides valuable space to accommodate electronics, through-hole wiring or other aspects of the payload.

LS Series slotless motor kits are perfect for gimbal applications, airborne or otherwise. Even ground-based systems, vehicle-mounted turrets, spacecraft imaging systems and pan-tilt-zoom (PTV) security systems can benefit.

Features summary of LSI-Series Motors:

• cogging-free for smooth and precise motion
• low weight
• large through hole
• high peak torque and highest torque density
• suitable for low speed operation e.g. in universal joints, robotics, beam control, optical platforms
• low total harmonic distortion (<1% in back EMF)
• precise phase balance with sinusoidal drive, resulting in: extremely low torque ripple
• frameless motor kits for deep integration

A Reaction Wheel is an actuator for controlling the position of a satellite. The reaction wheel exerts a torque to rotate the satellite along the same axis but in the opposite direction. A reaction wheel consists of an electric motor, a flywheel mass rotated by it, and control electronics for determining the speed of the motor. Unlike motors or electromagnetic coils, which change the spin of the system, the overall spin of the satellite system remains constant. The cogging-free ThinGap motor sets of the TG-Series are particularly suitable for the position control of a satellite.

The TG-Series motors have the following features:

• incomparable smoothness of rotation
• low profile
• low weight
• high torque density
• compact, highly integrated design
• almost zero noise
• cogging-free and precise speed control
• high speed, high efficiency due to absence of iron losses
• small footprint, including low outgassing components
• large through hole
• high torque to weight ratio
• scalable and customizable option available

The cogging-free motors are also often used to generate a precise linear movement from a rotary motion. This is particularly important for mask inspection in the semiconductor industry. The principle is called friction rod drive and works as follows.

• The shaft of the cogging-free motor presses on a metal rod (frictional contact between two metal surfaces)
• Shaft and rod are hardened to minimize mechanical deformation
• The motor shaft has two paired bearings (2x2) to eliminate radial play
• These are specially paired bearings, which must have a very similar tolerance
• Feedback: resolver + DC tacho
• Drive electronics: MACCON LWM, a non-switching servo drive (a.k.a. "linear amplifier")
• There is no heat generated in the rod, because the rod has no electric coils and is therefore completely passive.

Another application of the cogging-free motors is wafer polishing. Due to the absence of cogging torque, a high speed smoothness is achieved. This leads to a high surface evenness on the semiconductor wafer.

Contact us to talk to an experienced MACCON engineer about your application.

Robot-assisted surgical systems require smooth precision movements in the robot joints and end effectors. The LS series cogging-free motors are particularly suitable for this purpose. The motor's slotless annular stator lamination package results in precise cogging-free rotary motion and high synchronization. The motors' large inner bore also allows cables and hoses to be routed smoothly through the robot joints.
The characteristics of the LS series cogging-free kit motors meet the required standards of medical technology manufacturers.

Also in the field of drive electronics MACCON offers suitable solutions for the demanding applications in medical robotics. On the one hand capacitive encoders in kit form for robotics and on the other hand integrated servo controllers for robotics.

When control engineers contemplate difficult tasks such as micrometre / nanometre positioning, as well as aiming for speed stability at very low speeds, they usually think about several key success factors.

Firstly, eliminating cogging force or cogging torque. This is easily achieved by using cogging-free motors such as the ones shown on this page. In addition, it is well known that a high-resolution encoder system is required. This could be an optical encoder system, such as the ones shown at this link. Finally, they consider the type of servodrive which should be used. Most servodrives use pulse-width modulation of the supply voltage to achieve the required current in the motor windings. However, this leads to current ripple, which in turn produces torque ripple. The torque ripple makes it impossible to achieve high-precision servo tasks. The solution is to use a non-switching servodrive, also known as a linear amplifier. The MACCON Family of non-switching servodrives can be found at this link.

With the following success factors in place:

• Ironless motor
• High-resolution optical encoder
• Non-switching servodrive (linear amplifier)

we can now look at the remaining puzzle pieces. Of course, we should never forget the issue of cables. High-quality motor and feedback cables which are properly shielded against electromagnetic interference are a must. Last but not least, we need an experienced commissioning engineer to get the described system working. MACCON has a core team of experienced engineers who have supported machine-builders in semiconductors and optics / photonics to achieve the most difficult of nanometre positioning and low-speed motion tasks. Contact us to discuss your needs, engineer-to-engineer!