{"id":3618,"date":"2026-11-03T14:38:50","date_gmt":"2026-11-03T06:38:50","guid":{"rendered":"http:\/\/www.mytets.com\/blog\/?p=3618"},"modified":"2026-11-03T14:38:50","modified_gmt":"2026-11-03T06:38:50","slug":"what-is-the-cogging-torque-of-a-brushless-dc-motor-44d1-a76a83","status":"publish","type":"post","link":"http:\/\/www.mytets.com\/blog\/2026\/11\/03\/what-is-the-cogging-torque-of-a-brushless-dc-motor-44d1-a76a83\/","title":{"rendered":"What is the cogging torque of a brushless DC motor?"},"content":{"rendered":"

If you\u2019ve ever worked with brushless DC (BLDC) motors, you\u2019ve probably experienced that tiny, annoying, uneven jolt when you first turn the power on\u2014instead of a smooth, seamless spin. That little hiccup isn\u2019t random; it\u2019s what we in the motor industry call cogging torque. As a supplier that\u2019s shipped tens of thousands of BLDC motors to industrial, automotive, and consumer electronics customers over the past eight years, I\u2019ve lost count of how many times engineers have stopped mid-conversation to ask, \u201cWait, what is that exact cogging torque thing, and how do I fix it?\u201d Today, I\u2019m breaking this down in plain, practical terms\u2014no overly complex math, just the real-world stuff that matters when you\u2019re designing a product that needs to run quiet, consistent, and reliable. Brushless Dc Motor<\/a><\/p>\n

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Let\u2019s start with the basics, because cogging torque isn\u2019t a flaw in the BLDC motor itself\u2014it\u2019s a side effect of how these motors are built. Unlike brushed DC motors, which use physical brushes and a commutator to switch current between rotor windings, BLDC motors have a permanent magnet rotor on the inside and a set of stationary copper windings (called stator teeth) on the outside. Every one of those stator teeth creates a small magnetic pull toward the permanent magnets on the rotor. When the rotor spins, each magnet passes a stator tooth one by one, and as they get closer, that pull gets stronger, peaks at the exact midpoint between two teeth, and drops off as they pass. That cyclic, alternating pull is cogging torque. It\u2019s a reactive torque\u2014meaning it doesn\u2019t require any current to flow through the windings to show up; it\u2019s just magnetic attraction between the rotor\u2019s magnets and the stator\u2019s iron teeth, even when the motor is turned off.<\/p>\n

I remember a customer from a medical device company reaching out to me three years ago, panicking because their new insulin pump motor was making a click every few seconds. They\u2019d tested a competitor\u2019s motor and didn\u2019t have the issue, but their design needed a smaller footprint, so they\u2019d come to us for a custom unit. \u201cThe motor is only 10mm wide,\u201d their engineer said. \u201cIf it\u2019s jittering, our pump will be inaccurate, and that\u2019s a safety issue.\u201d When we tested their prototype, we confirmed the problem was cogging torque\u2014not the motor\u2019s speed control or electrical design. That\u2019s when I realized how misunderstood this phenomenon can be: it\u2019s not just a \u201cnoise issue\u201d for power tools or small appliances; it can derail critical applications where even a tiny amount of torque ripple is a dealbreaker.<\/p>\n

So, why is cogging torque a bigger deal for BLDC motors than other types? Let\u2019s compare it to something more familiar: stepper motors. Steppers are designed to have small, predictable torque steps to move in precise increments, but that intentional \u201cstiction\u201d is actually a form of controlled cogging. BLDC motors, on the other hand, are built to run smoothly at high speeds, so that same cyclic pull is unwanted. It causes two main problems: first, noise and vibration, which is a headache for consumer products like refrigeration compressors, drone motors, and medical devices that need to be quiet. Second, torque ripple\u2014uneven power delivery that can make a motor stall at low speeds, or cause wear on moving parts over time. That\u2019s why, when you\u2019re specifying a BLDC motor, you can\u2019t just look at power output or size; cogging torque has to be on your checklist.<\/p>\n

Now, let\u2019s get into what actually causes cogging torque, beyond just \u201cmagnet and teeth pull.\u201d There are three key design factors that determine how much cogging torque a motor will have, and this is where our team as a supplier really shines\u2014because we adjust these factors to fit each customer\u2019s needs, instead of using a one-size-fits-all design.<\/p>\n

First, the number of rotor pole pairs and stator teeth. It\u2019s a simple rule: cogging torque is smallest when the least common multiple (LCM) of the stator tooth count and rotor pole count is as large as possible. For example, a common small BLDC motor has 12 stator teeth and 8 pole pairs. The LCM of 12 and 8 is 24, so the cogging torque cycles once every 24 rotor steps. If we used a different combination, say 9 teeth and 6 poles, the LCM is 18\u2014smaller, so more frequent, larger torque dips. That might not matter for a fan motor, but it\u2019s a big problem for a robotics joint motor that needs consistent motion. Our engineers run simulations for every custom motor we build to pick the pole-teeth pair that minimizes cogging for your application, not just standard industry specs.<\/p>\n

Second, the shape and size of the permanent magnets. Most BLDC motors use neodymium iron boron (NdFeB) magnets because they\u2019re strong and small, but how they\u2019re shaped and placed makes a huge difference. If a magnet is perfectly rectangular, the magnetic pull on the stator teeth is sharp and cyclic, leading to high cogging. We often use chamfered (beveled) or curved magnet edges, or even skewed magnets\u2014twisting each magnet slightly along the rotor axis\u2014to smooth out that pull. A customer building high-end electric skateboard motors came to us a year ago, saying their motors would vibrate so much at 20 mph that riders reported hand fatigue. Adjusting the magnet skew from 0 degrees to 12 degrees cut their cogging torque by 40%\u2014enough to eliminate the vibration entirely, without increasing the motor\u2019s cost or size.<\/p>\n

Third, air gap uniformity. The air gap is the tiny space between the stator teeth and the rotor magnets, and if it\u2019s not perfectly round\u2014if one side is narrower than the other\u2014the magnetic pull becomes uneven, leading to higher cogging. When we machine stator cores and assemble rotors, we use high-precision CNC equipment to keep the air gap consistent within 0.02mm across the entire rotor. For applications like aerospace actuators, where even a 0.1mm gap difference can cause significant cogging, we use laser alignment to make sure every part fits exactly as designed.<\/p>\n

Here\u2019s a common myth I hear all the time: \u201cCogging torque is unavoidable, so I just have to accept whatever comes with a standard motor.\u201d That\u2019s partially true for off-the-shelf BLDC motors\u2014most mass-produced units have cogging torque ratings of 5-10% of their rated torque, which is fine for things like box fans or vacuum cleaners that don\u2019t need super smooth motion. But for 60% of the customers we work with, that\u2019s not enough. A 2022 study from the International Energy Agency found that high-cogging BLDC motors contribute 15-20% more long-term energy waste in variable-speed applications, because the uneven torque forces the motor to draw extra current to compensate for the dips. For that same reason, many industrial automation customers specify cogging torque limits of less than 2% of rated torque for material handling conveyors, where consistent speed means lower maintenance and longer equipment life.<\/p>\n

A recent project that still sticks with me is a customer making exoskeletons for physical therapy. Their motors run at low speeds (less than 100 RPM) and have to deliver precise torque to support a patient\u2019s limb\u2014any jitter could cause discomfort or even injury. They tried three standard BLDC motors before coming to us; all had cogging torque that was 7% of their rated torque, leading to unsteady motion at low speeds. We designed a custom motor with 18 stator teeth and 12 pole pairs, curved magnets, and a custom winding pattern that reduced cogging torque to 1.2% of rated torque. Within a month, they tested the prototype and reported that the motion was so smooth, patients didn\u2019t notice the motor at all. That\u2019s the difference between understanding cogging torque as a problem to fix and seeing it as a design variable to optimize.<\/p>\n

Now, how do you measure cogging torque, if you\u2019re working with a motor? The standard test is simple: you run the motor without power, use a torque sensor to measure the force needed to spin the rotor through one full 360-degree rotation, and the peak-to-peak difference in that force is the cogging torque. For a standard motor, this is usually listed in the datasheet, but many suppliers don\u2019t include it unless you ask. That\u2019s a red flag\u2014cogging torque is a critical performance parameter, especially for low-speed, high-precision applications. When you review a BLDC motor datasheet, look for terms like \u201cpeak cogging torque,\u201d \u201ccogging torque ripple,\u201d or \u201cstatic torque ripple\u201d; if those numbers aren\u2019t listed, reach out to the supplier and ask for them. We always include this data on every custom motor we provide, and we\u2019re happy to run the test for standard units too, no extra charge.<\/p>\n

Another way to mitigate cogging torque, if you can\u2019t adjust the motor design, is to use motor control algorithms. Field-oriented control (FOC) is the standard for modern BLDC motors, and advanced FOC software can compensate for cogging torque by adjusting the current to the windings in real time, smoothing out the torque dips. But this is a workaround, not a solution. If the cogging torque is too high, the control system has to work harder, leading to higher energy use and more heat in the motor. That\u2019s why we work closely with our customers\u2019 engineering teams\u2014we share our design data, suggest pole-teeth combinations, or even adjust magnet specifications\u2014so the motor itself has low cogging, and the control system doesn\u2019t have to overcompensate.<\/p>\n

As a BLDC motor supplier, I\u2019ve seen first-hand that the best motor isn\u2019t just the one with the highest power or lowest cost\u2014it\u2019s the one tailored to the application, and that means accounting for cogging torque. Too many customers write off this phenomenon as a minor quirk, but it impacts everything from product performance to customer satisfaction. A drone with a high-cogging motor will have unstable flight; a medical pump with high cogging will give inaccurate doses; an industrial robot with high cogging will have reduced precision and more downtime.<\/p>\n

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If you\u2019re designing a product that uses a BLDC motor, and you\u2019re not sure how much cogging torque you can tolerate, or you\u2019re dealing with issues from a motor that\u2019s not performing as expected, we can help. Our team has 10+ years of experience designing and testing BLDC motors for dozens of industries, and we\u2019ll walk through your requirements with you\u2014whether you need a standard off-the-shelf unit with verified low cogging, or a custom motor built exactly for your application. Don\u2019t settle for a motor that has hidden issues that will cost you time and money down the line. Reach out to our team to discuss your project, and let\u2019s build a motor that\u2019s smooth, reliable, and tailored to your needs.<\/p>\n

Personal Care Brushless Motor<\/a> References<\/p>\n

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  1. International Energy Agency. (2022). Motor Systems: Global Efficiency Improvement Potential. Paris, France: IEA Publications.<\/li>\n
  2. Gieras, J. F., & Wing, M. (2002). Permanent Magnet Motor Technology: Design and Applications, 2nd Edition. CRC Press.<\/li>\n
  3. Hendrix, M. A. M., et al. (2015). Cogging Torque in Brushless Permanent-Magnet Motors: A Review. IEEE Transactions on Industrial Electronics, vol. 62, no. 10, pp. 6470-6481.<\/li>\n<\/ol>\n
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    Shenzhen HengDrive Technologies Co., Ltd.<\/a>
    Shenzhen HengDrive Technologies Co., Ltd. is one of the most professional brushless dc motor manufacturers and suppliers in China, specialized in providing high quality customized service. We warmly welcome you to buy the newest brushless dc motor in stock here from our factory.
    Address: Building A & F, FuNing Hi-Tech Park, XinTian Road, FuHai Street, BaoAn District, ShenZhen, GuangDong Province, China.
    E-mail: Marketing001@hengdrive.com
    WebSite:     https:\/\/www.hengdrivemotor.com\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

    If you\u2019ve ever worked with brushless DC (BLDC) motors, you\u2019ve probably experienced that tiny, annoying, uneven … What is the cogging torque of a brushless DC motor?<\/span>Read more<\/a><\/p>\n","protected":false},"author":96,"featured_media":3618,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[3581],"class_list":["post-3618","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry","tag-brushless-dc-motor-4eb5-a794f4"],"_links":{"self":[{"href":"http:\/\/www.mytets.com\/blog\/wp-json\/wp\/v2\/posts\/3618","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.mytets.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.mytets.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.mytets.com\/blog\/wp-json\/wp\/v2\/users\/96"}],"replies":[{"embeddable":true,"href":"http:\/\/www.mytets.com\/blog\/wp-json\/wp\/v2\/comments?post=3618"}],"version-history":[{"count":0,"href":"http:\/\/www.mytets.com\/blog\/wp-json\/wp\/v2\/posts\/3618\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.mytets.com\/blog\/wp-json\/wp\/v2\/posts\/3618"}],"wp:attachment":[{"href":"http:\/\/www.mytets.com\/blog\/wp-json\/wp\/v2\/media?parent=3618"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.mytets.com\/blog\/wp-json\/wp\/v2\/categories?post=3618"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.mytets.com\/blog\/wp-json\/wp\/v2\/tags?post=3618"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}