High Performance Zero-Cogging Motors For UAS Applications

Unmanned aerial systems of all sizes and shapes have varying requirements in terms of payloads and flight ranges. From Group 1 to 5 UASes, there is a need for electric motors offering high power, efficiency, and light weight for all forms of onboard actuation.

A graphic showing a graphic of a General Atomics MQ4 Reaper, next to the gimbal of a Northrop Grumman MQ-8C and a ThinGap LSI 75 slotless motor kit.

Multiaxial gimbals require high performance motors to directly drive their movements and hold position. In airborne systems, high performance is defined by Size, Weight, and Power (“SWaP”), as well as smooth motion. Gimbal makers have an inherent need for a high amount of torque, in some cases to move large payloads quickly and precisely and stabilize the housing against forces caused by aerodynamic drag. ThinGap’s LS Series of slotless motor kits is an industry leader for gimbal applications requiring high performance and efficiency, as well as decisive positioning and smooth motion. Their ring architecture allows for optimized optical designs, by allowing critical parts of the system, such as lenses or cabling, to be integrated through the large through hole in the center of the motor.

Another airborne application where ThinGap’s motor technology provides a competitive edge is as a starter-generator. There is a long-standing truism that good motors make good generators, and for starter-generator applications, ThinGap’s TG Series is the industry leader. This is enabled by the light wave-wound composite stator, and weight-optimized rotor with large clear internal aperture, which can be integrated into both piston and turbine engines. The TG Series offers high efficiency, high peak torque, low harmonic distortion, and weight optimization which are all desired traits. In the case of UAS applications, ThinGap motors can start the Internal Combustion Engine with its high peak torque, then switch to act as a generator to supply valuable conditioned power to onboard systems.

With more than two decades supporting airborne applications, ThinGap can produce motor kits to fit all size and power requirements. To learn more about ThinGap’s motors for airborne applications, click here.

ThinGap Demonstrates High Power Motor Capability with 100 kW Motor Kit

Showcasing ThinGap’s highly scalable slotless motor technology, the TGO 385 was designed with renewable energy in mind, but many potential applications exist.

ThinGap has completed its latest large-size motor prototype, the TGO 385 for a commercial customer. The TGO 385 motor kit has an outer diameter (OD) of 385 mm (15 in.), and an axial height of 223 mm (9 in.), making it about the same volume as a 5-gallon bucket.  The power output capability of the TGO 385 is estimated to be 100 kW or more depending on the application.

Showcasing the highly scalable nature of ThinGap’s motor architecture, the TGO 385 is the newest variant of the TG Series of slotless motor kits. The company’s TG motors are unique in having a stator architecture with an ironless coil. Due to the absence of slots or “teeth”, ThinGap’s stators do not saturate during operation, allowing the motor kit to produce more torque as current is applied, without the falloff seen in traditional iron core motors. Combined with a mechanical design that promotes convective cooling during operation means that the TG Series has unrivaled power density.

The TG Series has been successfully used in a wide variety of generator, propulsion, and flywheel applications, ranging from gyro-stabilization in boats and satellites to airborne starter-generators. To learn more the highly efficient, zero-cogging TG Series of slotless motor kits, click here.

The TGO 385 demonstrates ThinGap’s ability to deliver tailor-made high-power solutions.  With more than two decades of experience in the design and production of slotless motor kits, ThinGap leverages its proven designs and analytical modeling that results in highly accurate transitions from predicted performance to real world operation. Furthermore, the process steps needed to produce motors of all sizes is highly scalable, and ThinGap has shipped large class motors of up to 600 mm OD, ranging from 10-400 kW of output power.

NASA’s ERBS and the Future of Weather Satellites

January 2023 marked the quiet end of NASA’s ERBS (Earth Radiation Budget Satellite). Launched in late 1984 from Space Shuttle Challenger during mission STS-41-G, ERBS was launched to study how the Sun’s energy was absorbed and reflected by the Earth, as well as carrying other payloads designed for atmospheric study.

A graphic showing the ERBS satellite in orbit, next to a photo of the liftoff of the Space Shuttle that put it in orbit in 1984, with the caption "NASA ERBS 1984-2023"

Originally designed for just a two year operational lifespan, ERBS far outlived this by 19 years until it was retired in 2005. What made ERBS one of NASA’s most important satellites was the SAGE II instrument, that was critical in observations confirming the depletion of the Ozone layer due to CFC usage, ultimately resulting in their ban. After exhausting its onboard propellant and energy stores, NASA decommissioned the satellite in 2005, and through the end of 2022 it orbited the Earth before burning up during atmospheric re-entry near the Alaska.

Though ERBS’s story may have ended, it helped reinforce the importance of using satellites for atmospheric observations and experimentation. ThinGap is a proud supplier to NASA’s upcoming PACE (Plankton, Aerosol, Cloud, ocean Ecosystem) mission, set to launch from Cape Canaveral in early 2024 aboard a SpaceX rocket. ThinGap’s LS Series of slotless motor kits are part of the OCI (Ocean Color Instrument) advanced spectrometer designed to measure the color of the ocean in wavelengths from ultraviolet to infrared frequencies.

ThinGap Demonstrates Small Motor Capability With The TGR 29

With the smallest stator yet, the TGR 29-12 demonstrates the scalability of ThinGap’s slotless motor technology

ThinGap has delivered its latest small-size product, the TGR 29-12, to several commercial customers. The TGR 29-12 motor kit has an outer diameter (OD) of 29 mm and an axial height of just 12 mm, providing a continuous in-vacuum torque output of 0.0028 N-m, and a peak torque of 0.034 N-m. A complete datasheet is available on ThinGap’s website.

With a total part mass of 31 grams, and a coil OD of 19.2 mm, the TGR 29-12 has the smallest stator of any ThinGap motor to date, showcasing the company’s highly scalable architecture. Designed for Attitude Control in CubeSat applications, the new part continues the build out of the Space focused TGR product line.

Prior TG Series models have been widely used in Reaction Wheel Assemblies (RWA), due to a patented architecture’s inherent advantages when used in any type of flywheel applications. Because of the efficient lightweight ironless core, zero-cogging stator, and high power-to-weight ratio, the TGR 29-12 offers more than double the torque of the closest competitor with minimal losses and no radial forces between the stator and rotor.

With more than two decades of experience in the design and production of slotless motor kits, ThinGap can leverage proven designs and analytical modeling that results in highly accurate transitions from predicted performance to real world operation. Furthermore, the process steps needed to produce motors of all sizes is highly scalable; ThinGap has shipped motors from 19 mm up to 600 mm in size.

For additional information on custom motor development, please contact us.

Record Breaking Direct Drive Turntables Powered By ThinGap

What do Formula 1 race cars, satellites, surgical robots, and high-end turntables have in common?  All have benefitted from the low profile, smooth motion, and highly linear output of ThinGap’s slotless motor kits. One application that has gotten our attention has been our friends at VPI Industries, who have leveraged the benefits of cogless motors for their turntables.


Over the last decade, music enthusiasts have rediscovered the authentic, warm sound of vinyl records, even in the era of convenient streaming. For high-end turntables, direct-drive motor designs ensure reliable and consistent motion for music playback through Hi-Fi systems. Historically turntables have been belt-driven, which though cost-effective, wear down over time affecting music playback and requiring replacement. While more expensive, “direct-drive” turntables get around this by mounting the record platter directly to the motor, making it more reliable as well as having smoother playback.

Precision direct-drive motors, such as those made by ThinGap are an ideal solution for modern turntables. A high-performance stereo system is nothing without clean input sources, and ThinGap’s smooth, zero-cogging motion profile is key to precise playback. Another contributing factor to the long-standing relationship between VPI and ThinGap has been the shared pride in American-made products. Since the beginning, VPI has been both sourcing components from American suppliers, as well as manufacturing their turntables in-house in New Jersey.

The re-emergence of demand for vinyl records, especially by audiophiles has shown that you can’t be too sentimental, and that when music is played on a modern direct-drive turntable it sounds better than it did when new. No matter if you’re listening to the next phase, new wave, dance craze, so long as there is a ThinGap motor powering a VPI turntable, it’s still rock and roll to us.

Optical Platforms, A Perfect Fit

Central to the deployment of cutting edge technologies that require dynamic sensors and precision photonics, such as self-driving cars, laser communication, and medical equipment, optical stages are at the core of these systems. Optical systems often require precise, highly linear and cogless brushless DC motors to actuate lenses and prisms for directing laser beams, or to collect light need in high speed communications, sensing, or scanning.

An optical platform refers to any instrument that relies on photons to transmit, receive, or direct energy. Common forms of optical platforms include metrology instrumentation, medical diagnostics, inspection equipment, free-space laser communication, as well as LiDAR scanners.

Optical Communications Terminals (OCT), used in both terrestrial and space-based applications are a kind of gimbaling device that transmit and receive data through free space. Mounted on a turret, these devices use highly collimated light generated by lasers to communicate at high rates of speed, over long distances, including in satellite-to-satellite communication. ThinGap’s LS Series of slotless motor kits is an industry leader for gimbal applications requiring high performance and efficiency, as well as decisive move-and-hold positioning, and smooth motion for long-range target lock. LS motors have been widely used in OCT systems and even NASA’s PACE Mission’s optical scanner.

The emergence of self-driving vehicles and other unmanned systems has been enabled by the integration of LiDAR technology. LiDAR is an acronym that stands for Light Detection And Ranging, and operates by projecting out laser energy and then measuring the time it takes for it to be returned. LiDAR platforms benefit from slotless motor technology, such as ThinGap’s TG series that combines extremely precise and controlled movement, high speed, and a large throughhole needed for tight integration.

Broader use of optical systems includes laser guidance and directed energy for the military, scientific spectroscopy, and medical treatment and diagnostics. Industrial segments, like semiconductor wafer processing and test heavily rely on the precision of optical systems, as does material processing. In most cases, to leverage the precision of highly collimated light and highly sensitive sensors, precision actuation is need in the form of smooth motion profiles, highly linear torque constant and little or no hysteresis caused by the motor.

Low profile and high torque air-core motors are a perfect fit for many optical systems. With a large through hole, lenses or prisms can be integrated inside the footprint of the motor. Precision, cogless motion is demanded in both transmission and receipt of photonic signals, and quality, qualification for medical or space and reliability go together with these targeted applications.

ThinGap’s LS and TG Series of motor kits come in sizes from 25 mm up to 267 mm OD, with modified and full custom options are also available. All ThinGap motors are zero cogging and have a thin coil, with a large through-hole. The LS Series are designed for torquer motor applications, and feature a steel lamination stack that retains the stator coil, and ideal thermally efficient architecture for clamping or bonding into systems. The TG Series offers both high speed and high torque performance, and is ideal for haptic feedback because its ironless stator produces no attractive forces when unpowered.

ThinGap Marks the First Customer Deliveries of the Newest LS Series’ 39mm by 39mm Cogless Motor Kits

A new, taller variant of the LSI 39 frameless motor kit now means three sizes with a 39mm OD
Unique in that the part it is as tall as it is wide, resulting in very high torque despite its small size

ThinGap has delivered the first production units of its newest LSI 39 motor kits to customers. The new LSI 39-39 motor kit has an outer diameter (OD) of 39mm and also an axial height of 39mm; the height is more than double that of its sister product the LSI 39-17, and nearly quadruples that of the LSI 39-10. This increase in axial height more than doubles the continuous and peak torque outputs to 0.279 N-m and 1.020 N-m, respectively, compared to the LSI 39-17.

The LSI 39-39 can operate at speeds from 0-4,600 RPM and has a motor constant of 0.05 Kt. Thanks to the LS Series’ steel lamination stack architecture that retains the highly precise wave-wound stator coil, all LS products provide an excellent thermal path when clamped or bonded as part of system integration.

ThinGap’s customers for the LS and TG Series of motor kits consistently take advantage of the product lines’ inherent zero cogging motion, low profile and large through hole. The architecture of both product series yields a highly linear torque output, and little or no hysteresis.

The LSI 39-39, like all the small to medium-sized LS products is targeted at torquer motor applications in robotics, gimbals, and precision industrial systems, including semiconductor production and metrology equipment. With outer diameter sizes from as small as 25mm, and up to 267mm, the LS line ranges in continuous torque from 0.1 N-m up to 12.0 N-m. Standard, modified, and full custom designs are available in both in-runner and out-runner configurations.

To read the full press release, click here.

TG Series for Starter-Generator Applications

There is a long-standing truism that good motors make good generators.  High efficiency, smooth operation, low harmonic distortion and weight optimization are commonly desired traits in both motors and generators. In the case of a starter-generator for applications like UAVs and ground-based portable systems, ThinGap motors can start an Internal Combustion Engine (ICE) with its high peak torque, then switch to generator mode to supply valuable conditioned power to onboard systems. What is effectively two functions from one electro-mechanical device.

An image of a UAV with a motor kit used as a starter-generator

ThinGap designs and builds high efficiency, air core-slotless motor kits with large through-holes and high-torque and power density. This architecture largely eliminates internal magnetic losses by virtue of design and offers the highest possible BLDC system efficiency (up to 95%).  The low impedance Stator provides a stable, pure 3-phase sinusoidal, low-droop (less than 1% harmonic distortion) voltage output. Because of the thin radial cross section and with an optimized Rotor, the bulk of the material is at the maximum radius yielding high torque.

As part of its ongoing support of Government end-customers, ThinGap and its industry partners were recently selected for two different airborne starter-generator projects for use on DOD platforms. ThinGap has been supplying starter-generators for several years, and recently has worked to expand offerings and more widely deploy these solutions. There is growing demand, especially in Defense, for generators that run off a heavy full engine.

To better understand ThinGap’s position in supplying electric motors for starter-generators, it helps to understand starter-generators. Starter-generators are a unique application that requires high peak starting torque at relatively low speed, and then power generation at high speed. Aircraft require starter-generators to begin operation, where on startup in both piston and jet turbine powered aircraft, power is drawn from onboard batteries to operate the starter-generator first as a motor to get the main engine up to a speed that can sustain combustion for propulsion. This process takes a few seconds on piston motors and up to a minute with jet turbines. Once combustion has been sustained, current is cut to the starter, and from there the free-spinning rotor is driven by the crankshaft or turbine shaft to now act as a generator to power aircraft systems and recharge the aircrafts internal power supply from startup.

ThinGap’s TG Series is ideal for starter-generator applications. This is enabled by the lightweight wave-wound composite Stator, and weight-optimized Rotors with large clear internal apertures which can be integrated into both piston and turbine engines. For the TG Series, peak torque capacity is much higher, giving a dynamic response significantly better than the competition at a lighter weight.

The TG Series is air cooled by convection, and unlike most motor kits generates more power the faster it is spinning, due to faster airflow over the composite coil, and power ranges between 3-7 kW when used as a starter-generator, and standard offerings range between 5 and 7 inches in diameter, with custom motors delivered for UAV applications as large as 14 inches.

To learn more about ThinGap’s TG Series of motor kits, click here.

What is Cogging Torque?

As the primary feature and the focus of ThinGap’s product lineup, a lot has been spoken about zero cogging torque in the product lineup. Cogging torque is the interaction between the permanent magnets in the rotor, and the slots of the stator. Because the rotor magnets are attracted to the stator teeth, the torque required to move the rotor changes with the relative position of the rotor to the stator. In other words, additional energy is required to break the position dependent detent torque to advance the motor.

Cogging torque adds harmonic content to the torque-versus-angle curves for each phase. When driven by a sinusoidal current, harmonic content of the torque-versus-angle curves cause undesirable variations in torque production that interfere with smooth motor rotation. Additionally, phase imbalance common in a traditional slotted motor can further exacerbate the issue. The result is a phenomenon known as torque-ripple which is a variation of torque production with position.

There are a few issues when trying to integrate a traditional cogging motor into an application that requires precision actuation. To mitigate cogging torque in a slotted motor, it is possible to design the lamination stack with a rotational skew, so the magnetic field of the stator is diagonal to that of the magnetic field of the rotor. Alternatively, the magnets can be designed with a skew. Other techniques include using different slot-pole combinations and compensating for cogging and phase imbalance in the drive electronics.

However, when integrating slotted motors into systems for precision actuation, there will always be issues. Due to the nature of manufacturing, there is always variance between two seemingly identical motors, which can have an unpredictable impact on the cogging profile and phase balance. Furthermore, solutions to minimize cogging torque typically reduce the total output of the motor. The sunk cost of trying to mitigate cogging torque on both motor costs and development labor is better spent on the correct solution: slotless, coggless, brushless DC motors from ThinGap.


The benefit of ThinGap slotless and ironless motor designs is that they eliminate cogging torque by design. Their uniquely constructed phase windings produce a balanced phase amplitude and angle relationships between phases. This results in less than 1% total harmonic distortion of the back EMF waveform which minimizes torque ripple when paired with sinusoidal drive electronics.

A graph depicting normalized torque-vs-angle curves, with 1% phase imbalance.

ThinGap’s slotless motor architecture with wave-wound coils prevents cogging since the air-core rotor has no slots. Wound around a flat bobbin with a basket weave style winding, ThinGap’s composite air core motor kits have no iron. The thin nature of the coils produces very high copper packing and a motor with a large through hole, up to 80% of the outer diameter. In addition, ThinGap’s motor kits are available with Halbach array rotors, optimizing the magnetic flux for the highest torque density in a slotless motor.

To learn more about zero-cogging motion solutions, please contact us.

ThinGap’s TG Series for Flywheel Applications

For many years, ThinGap motors have been successfully used in a variety of flywheel applications, ranging from gyro-stabilization in boats and satellites, to momentum storage for renewable energy. ThinGap’s TG Series of slotless motor kits are ideal for flywheel applications because of their highly efficient lightweight composite stator, optimal balance between torque and inertia, with negligible rotational losses, and zero cogging that is critical to achieving smooth motion at high speed.

A photo montage detailing an exploded ThinGap TG motor kit, a sailing yacht, and a satellite above the earth, with the caption "Flywheel Momentum Storage"

Boats of all sizes stand to benefit from gyroscopic stabilization. Due to Newton’s third law of motion – every action carrying an equal and opposite reaction, a gyroscopes motion can be used to stabilize a ship or boat in heavy seas. A marine gyro-stabilizer is a large, spinning flywheel housed in the depths of the ship, near the keel. As the flywheel spins, computers on the bridge orient the flywheel against the ships current rolling motion, cancelling it out. ThinGap’s high efficiency motors make an excellent flywheel stabilizer of all sizes and can withstand harsh marine environments.

Another application where gyroscopic flywheels are used to change orientation is with satellites and their use of Reaction Wheel Assemblies. Yet another case of Newton’s Third Law, when a reaction wheel is spun up inside a satellite, the spacecraft turns in the opposite direction of the flywheel’s rotation, with this being used to steer and orient spacecraft in orbit. Because motion in space is multi-axial, each satellite carries multiple reaction wheels in an assembly to freely rotate. Since 2015, ThinGap has shipped thousands of kits for reaction wheel assemblies in large commercial and Government funded constellations, and in 2022, spun off their reaction wheel assembly motor kits to a separate product line.

An emerging use for highly efficient slotless motor kits is in momentum storage. Pioneered more than a decade ago for motorsports applications, excess or available energy is transferred to a motor that spins up a flywheel, whereby storing that energy in a rotating mass as a mechanical battery, instead of as chemical energy. Advantages of retaining the energy in a momentum flywheel application includes high power density compared with conventional batteries for quicker charge and discharge. Future applications of momentum storage could even extend to emerging markets such as renewable energy.

ThinGap’s ironless stator puts all the magnetics, the heaviest part of the motor, in the rotor. This maximizes the inertia for a given weight and size requirement, meaning the necessary flywheel mass can be reduced, and sometimes fully incorporated into the rotor, resulting in a lighter weight package for the same momentum storage capacity. Due to no iron saturation in the stator, ThinGap’s peak torque capacity is much higher for a similar weight motor, giving a dynamic response significantly better than the competition at a lighter weight.

To learn more about ThinGap’s TG Series of motor kits, click here.