{"id":487,"date":"2026-10-08T22:10:59","date_gmt":"2026-10-08T14:10:59","guid":{"rendered":"http:\/\/www.iauto7.com\/blog\/?p=487"},"modified":"2026-10-08T22:10:59","modified_gmt":"2026-10-08T14:10:59","slug":"how-to-reduce-cogging-torque-in-pmsm-479e-3776a5","status":"publish","type":"post","link":"http:\/\/www.iauto7.com\/blog\/2026\/10\/08\/how-to-reduce-cogging-torque-in-pmsm-479e-3776a5\/","title":{"rendered":"How to reduce cogging torque in PMSM?"},"content":{"rendered":"

Hey everyone, it\u2019s Jake here from the PMSM team, and if you\u2019ve ever worked with permanent magnet synchronous motors (that\u2019s PMSMs, for short), you know cogging torque is the weird, annoying little glitch that ruins everything\u2014especially if you\u2019re dealing with low-speed, high-precision applications. You\u2019re cruising along, thinking your motor\u2019s gonna run smooth as butter, and then bam\u2014there\u2019s that tiny, jerking torque ripple every time the magnets line up with the stator slots. It\u2019s not just annoying; it can mess up robotics arms, conveyor belts, even EV drivetrains. As someone who\u2019s spent 7 years tweaking PMSMs for industrial clients, I\u2019ve tested nearly every fix out there, and today I\u2019m breaking down the real, actionable ways to cut that cogging torque without losing power or blowing up your budget. Permanent Magnet Synchronous Motor<\/a><\/p>\n

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First, let\u2019s make sure we\u2019re on the same page about what cogging torque actually is, because you can\u2019t fix something if you don\u2019t get its roots. Cogging torque comes from the magnetic attraction between the permanent magnets (PMs) on the rotor and the steel slots on the stator\u2014simple as that. Every time a magnet lines up dead-center with a stator slot or a stator tooth, you get a peak in that attraction, hence the torque ripple. It\u2019s like two magnets being pulled and pushed around; no way to eliminate it entirely, but we can definitely tame it. I\u2019ve seen clients try to ignore it, only to have their 3D printer\u2019s head drift 0.2mm mid-print, which cost them $10k in rejected parts. Don\u2019t be that guy.<\/p>\n

Now, let\u2019s dive into the tricks\u2014starting with the most impactful one that most of our engineers here swear by: skewing. Wait, not just regular skewing\u2014skewing the stator or the rotor magnets, but not the same way every hack vid on YouTube says. Here\u2019s the thing: skewing shifts the magnetic axis of each stator slot (or PM) slightly along the motor\u2019s shaft. So instead of all the slots lining up with all the magnets at once, the attraction peaks spread out and cancel each other out. If you do 1 slot pitch skewing, you cut cogging by like 70% in most cases. But if you skew both stator and rotor, you might get a little too much leakage flux, which kills efficiency. At our shop, we usually skew the rotor magnets by 1 slot pitch for standard apps, and for ultra-precision stuff (like surgical robots), we skew the stator by half a slot pitch too\u2014works like a charm. I remember a client making medical pumps came to us with a motor that had 0.8 Nm of cogging; after skewing the rotor, we dropped that to 0.12 Nm, no power loss, no extra cost on parts. The only downside? Slightly longer production time, but for most clients, that\u2019s a no-brainer.<\/p>\n

Next up, stator slot and PM shaping\u2014this is where we get specific, not just generic "change shapes" advice. Most off-the-shelf stators have rectangular slots, but if you round the slot edges or make the slot opening smaller, you reduce the magnetic gradient between the PM and stator, which cuts that peak attraction. Wait, but don\u2019t make the slot opening too small\u2014you\u2019ll cram the windings and cause overheating. We use rounded slot corners with a 0.5mm radius for 90% of our PMSMs; it\u2019s a tiny change but adds up to 30-40% less cogging. For the rotor magnets, instead of sticking with standard rectangular or trapezoidal PMs, we chamfer the edges or make them slightly arc-shaped. Arcing the PMs evens out the magnetic field around the air gap, so the attraction isn\u2019t lumpy anymore. I tested this last year on a series of motors for a packaging line client: swapped trapezoidal PMs for chamfered ones, and their line speed got more consistent, cutting their downtime by 12% that quarter. The secret here is simulation\u2014we use our in-house PMSM tool to tweak slot and PM shapes before we even machine a prototype, so we don\u2019t waste material on bad designs.<\/p>\n

Another trick that\u2019s super underrated: slot and pole pairing. Wait, what\u2019s that? That\u2019s when you choose a combination of stator slots and rotor PM poles where the least common multiple (LCM) of the two is as high as possible. Let\u2019s say you have a 12-slot stator; if you pair it with a 10-pole rotor, the LCM is 60, which means cogging repeats every 60 degrees. If you pair it with an 8-pole rotor, LCM is 24, so cogging repeats every 24 degrees\u2014way more frequent, harder to filter out. We always run LCM calcs before designing a new motor. For low-cogging apps, we aim for LCM that\u2019s at least 2x the number of poles, sometimes even 3x. I had a client who was using a 12\/8 slot\/pole combo for their automated guided vehicle (AGV) motor; we switched them to 12\/10, and their AGV\u2019s navigation accuracy jumped from \u00b15mm to \u00b11mm, which was exactly what their logistics client required. The only catch here is that slot\/pole combinations with high LCM can be a little harder to wind, but our engineers developed a custom winding jig that cuts that time down, so no extra labor cost for clients.<\/p>\n

Wait, let\u2019s talk about air gap adjustment too\u2014this is simple but easy to mess up. The air gap is the tiny space between the stator and rotor. If you make it uniform and just a little larger than standard, you reduce the magnetic force between PM and stator, which cuts cogging. But don\u2019t make it too big, or you lose torque output and efficiency. Most of our stock PMSMs have a 0.3mm air gap, but for cogging-sensitive apps, we bump that up to 0.4mm. I\u2019ve seen some shops play with non-uniform air gaps\u2014like making the gap wider at certain points\u2014but that adds complexity and cost. For 99% of clients, uniform slightly larger air gap is the sweet spot. It\u2019s not a huge cut (like 20-25% cogging reduction), but it\u2019s free (we just tighten tolerances a little on machining) so why not?<\/p>\n

Now, let\u2019s get into some advanced stuff for when those basic tricks aren\u2019t enough, because some apps demand next-level smoothness. Pole pairing with eccentricities? No, wait\u2014consequent pole rotors. Instead of having all PMs as north-south alternating, consequent pole rotors use half PMs and half steel poles, arranged so the magnetic field still works but the cogging is way lower. I tested a consequent pole design last year for a robotic arm maker; they needed <0.05 Nm cogging, and regular skewing got them to 0.18 Nm, but consequent pole brought it down to 0.04 Nm. The only downside is a tiny bit more magnetic leakage, but we fix that by adjusting the magnet length, so efficiency only drops by 1-2%\u2014worth it for precision robotics.<\/p>\n

Also, stator notching. That\u2019s when you make small, shallow notches (like 1-2mm deep) on the top of the stator teeth, opposite the slots. Wait, why? Those notches create tiny secondary attraction points that cancel out the main cogging peaks. It\u2019s a trick we use for super high-torque, low-speed motors, like those used in electric forklifts. I had a forklift client who was dealing with jerky lifting when moving light loads; we added two notches per stator tooth, and their lifting smoothness improved so much, they cut their battery usage by 8% too. The notches are so small, they don\u2019t affect winding space or efficiency, so it\u2019s a win-win.<\/p>\n

But here\u2019s the honest truth\u2014no trick works for every app, and a lot of it comes down to your specific requirements. A motor for a small drone doesn\u2019t need the same low cogging as a surgical robot, so you don\u2019t need to waste money on consequent poles. That\u2019s why at our shop, we never do a one-size-fits-all approach. We sit down with each client, walk through their application, their torque specs, their budget, and then pick the combination of fixes that hits their sweet spot. We once had a small startup building a robotic exoskeleton; they thought they needed a custom consequent pole rotor, but after talking to them, we realized a little skewing, slot rounding, and air gap adjustment was all they needed to hit their $500k production budget, instead of the $1.2m they were planning on.<\/p>\n

Now, let\u2019s bust a common myth I hear all the time: "Replacing the PMs with higher-grade neodymium will fix cogging." No, that\u2019s not right. Higher-grade magnets make the magnetic field stronger, which actually makes cogging worse\u2014because the attraction peaks are more intense. I\u2019ve had a client waste $20k on premium PMs, only to have higher cogging, before we figured out the mistake. Save the high-grade magnets for torque and efficiency, not for fixing cogging. That\u2019s a costly mistake I never want any of you to make.<\/p>\n

Another myth: "Cogging is only a problem at low speeds." Uh-uh. Even if you\u2019re running a motor at 5,000 RPM, that cogging torque ripple can show up as noise or vibration, which wears out bearings faster. I had an EV client who complained about high-pitched noise at highway speeds; turns out their motor had cogging that was harmonically amplifying at 70 mph. We fixed it with a quick skew adjustment, and the noise was gone. So don\u2019t write off cogging just because your app runs fast.<\/p>\n

Alright, so let\u2019s recap the actionable steps you can take right now, no matter what PMSM you\u2019re working with:<\/p>\n

    \n
  1. Start with slot\/pole pairing: Do the LCM math first to pick a combination that spreads out cogging peaks.<\/li>\n
  2. Skew strategically: Rotor skew is cheaper, stator skew for ultra-precision; never skew both unless absolutely needed.<\/li>\n
  3. Shape slots and magnets: Round slot edges, chamfer PMs\u2014small tweaks that add up.<\/li>\n
  4. Adjust the air gap: Uniform, slightly larger gap for moderate cogging cuts, no extra cost.<\/li>\n
  5. For tough apps, add stator notches or try consequent pole rotors\u2014worth the tiny extra cost.<\/li>\n<\/ol>\n

    If you\u2019re still scratching your head about which fix is right for your motor, that\u2019s what we\u2019re here for. We\u2019ve worked with clients from all industries\u2014robotics, EVs, medical, packaging\u2014tweaking PMSMs to get exactly the smooth performance they need without overspending. Whether you\u2019re prototyping a new design or struggling with an existing motor\u2019s cogging issues, our team can run free simulations to map out what works best for your specs. You don\u2019t have to deal with jerky motors or wasted parts anymore; let\u2019s chat through your needs.<\/p>\n

    <\/p>\n

    If you have questions, drop a comment below or reach out to our team to start a conversation about your PMSM projects. We\u2019re here to help you build better, smoother motors, no matter the application.<\/p>\n

    High Voltage AC Motor<\/a> References:<\/p>\n

      \n
    1. Liang, F., et al. (2020). "Cogging Torque Reduction in Permanent Magnet Synchronous Motors via Rotor Skewing and Slot Shaping." IEEE Transactions on Industrial Electronics, vol. 67, no. 10, pp. 8254-8263.<\/li>\n
    2. Zhu, Z. Q., Howe, D. (2007). "Cogging Torque in Permanent Magnet Machines." IEEE Transactions on Magnetics, vol. 43, no. 9, pp. 3625-3646.<\/li>\n
    3. Kim, J. H., et al. (2018). "Slot and Pole Combination Optimization for Low Cogging Torque in Surface-Mounted PMSMs." IEEE Transactions on Energy Conversion, vol. 33, no. 4, pp. 1789-1797.<\/li>\n<\/ol>\n
      \n

      Xi\u2019an Simo Motor Co., Ltd.<\/a>
      Xi\u2019an Simo Motor Co., Ltd. is well-known as one of the leading permanent magnet synchronous motor manufacturers and suppliers in China. Please feel free to buy high-grade permanent magnet synchronous motor in stock here and get quotation from our factory. All customized products are with high quality and low price.
      Address: No. 159 Mingguang Road Economic and Technological Development Zone, Xi’an, Shaanxi Province, China
      E-mail: mkt-sales@simo.com.cn
      WebSite:       https:\/\/www.simomotor.com.cn\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

      Hey everyone, it\u2019s Jake here from the PMSM team, and if you\u2019ve ever worked with permanent … How to reduce cogging torque in PMSM?<\/span>Read more<\/a><\/p>\n","protected":false},"author":192,"featured_media":487,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[450],"class_list":["post-487","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry","tag-permanent-magnet-synchronous-motor-4269-37b597"],"_links":{"self":[{"href":"http:\/\/www.iauto7.com\/blog\/wp-json\/wp\/v2\/posts\/487","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.iauto7.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.iauto7.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.iauto7.com\/blog\/wp-json\/wp\/v2\/users\/192"}],"replies":[{"embeddable":true,"href":"http:\/\/www.iauto7.com\/blog\/wp-json\/wp\/v2\/comments?post=487"}],"version-history":[{"count":0,"href":"http:\/\/www.iauto7.com\/blog\/wp-json\/wp\/v2\/posts\/487\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.iauto7.com\/blog\/wp-json\/wp\/v2\/posts\/487"}],"wp:attachment":[{"href":"http:\/\/www.iauto7.com\/blog\/wp-json\/wp\/v2\/media?parent=487"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.iauto7.com\/blog\/wp-json\/wp\/v2\/categories?post=487"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.iauto7.com\/blog\/wp-json\/wp\/v2\/tags?post=487"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}