{"id":3568,"date":"2026-10-08T15:48:24","date_gmt":"2026-10-08T07:48:24","guid":{"rendered":"http:\/\/www.marquetearte.com\/blog\/?p=3568"},"modified":"2026-10-08T15:48:24","modified_gmt":"2026-10-08T07:48:24","slug":"how-to-measure-the-stall-torque-of-a-brushless-motor-4e0a-89c7af","status":"publish","type":"post","link":"http:\/\/www.marquetearte.com\/blog\/2026\/10\/08\/how-to-measure-the-stall-torque-of-a-brushless-motor-4e0a-89c7af\/","title":{"rendered":"How to measure the stall torque of a brushless motor?"},"content":{"rendered":"

Hey guys, it\u2019s Jake from your go-to brushless motor supplier \u2013 the one who\u2019s actually been messing with these motors long before they showed up in every RC car and drone on the market today. Let\u2019s cut to the chase: if you\u2019re here, you\u2019re probably deep in a project where you need to make sure your new brushless motor isn\u2019t gonna quit when the load gets real. That\u2019s where stall torque comes in, right? But here\u2019s the thing I see so many new builders (and even some seasoned ones) mess up: they Google a quick formula, grab a multimeter, and call it a day \u2013 and that\u2019s how you end up with a motor that\u2019s way weaker than you thought, or worse, fried it before you even got it installed. Brushless Motor<\/a><\/p>\n

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I\u2019ve lost count of how many times a customer hits me up panicking because their \u201c10 Nm stall torque motor\u201d delivered way less on their test bench. Most of the time, it\u2019s not that the motor is garbage \u2013 it\u2019s that they measured stall torque wrong. So today, I\u2019m walking you through exactly how to do this right, with stuff most people already have lying around (or can grab from your local hardware store for 20 bucks), and zero fancy lab equipment required. As a supplier, this stuff matters to me because if you spec our motor wrong, you\u2019ll be back buying a replacement in two weeks. No one wants that \u2013 not you, not me.<\/p>\n

First, let\u2019s make sure we\u2019re on the same page about what stall torque actually is, because if you mix this up with running torque, you\u2019re already off. Stall torque is the maximum twisting force a brushless motor can output when it\u2019s locked up<\/em> \u2013 like, the shaft can\u2019t rotate at all. If you\u2019ve ever held a drill bit against a piece of wood and felt the drill strain before it finally cuts through? That\u2019s stall torque in action. It\u2019s not the constant torque the motor makes while spinning \u2013 that\u2019s rated torque, which is lower and way more useful for everyday operation. Stall is the \u201cmake or break\u201d number; if your application needs to lift 20 kg, you don\u2019t want to guess at this.<\/p>\n

Now, before we dive into the steps, let\u2019s address the elephant in the room: why does this matter so much, especially if you\u2019re working with our motors? Here\u2019s the truth: brushless motors aren\u2019t like their brushed cousins. Their stall torque depends on two big things: how much current you feed them (overcurrent = higher stall torque, obviously), and how well you control that current (bad controllers = wonky numbers). I\u2019ve had customers try to use a cheap off-the-shelf ESC for a 20 Nm motor, and wonder why their stall torque was half what it should be \u2013 the ESC was limiting current to save itself. So when you measure, you\u2019ve gotta make sure your power supply is capable of delivering the peak<\/em> current the motor is rated for. For our motors, we list the stall current on every spec sheet \u2013 use that number, don\u2019t wing it.<\/p>\n

Alright, let\u2019s get to the actual test. I\u2019m gonna make this as simple as possible, no jargon that\u2019ll make your eyes glaze over. All you need is: your brushless motor, its matching ESC (we sell these with our motors, by the way \u2013 just saying), a power supply that can hit the motor\u2019s stall current (look for something with at least 2x the stall current rating, to be safe), a way to measure force (a luggage scale works, trust me), a long metal rod or a metal pipe that fits snugly on your motor\u2019s output shaft, and a way to lock the motor\u2019s shaft from spinning \u2013 a vise clamp or a C-clamp pair works great, just be gentle so you don\u2019t bend the shaft.<\/p>\n

Wait, hold up \u2013 safety first, always. I can\u2019t stress this enough: when you lock a motor\u2019s shaft and crank up the power, that current is gonna surge. Your power supply might hum loud, the ESC might get warm, and the motor\u2019s gonna vibrate like crazy. Don\u2019t hold anything metal near the shaft, don\u2019t stand directly in front of the rod, and never leave this test unattended for more than 10 seconds max. Overcurrent for too long can not only fry the motor\u2019s windings (which is a costly repair) but also cause the shaft to shear or the ESC to short. I\u2019ve seen a rod go flying once because a customer left it on for 30 seconds \u2013 we still talk about that. So safety: read the spec, don\u2019t exceed time, stay clear.<\/p>\n

Okay, test time. Step 1: Prep the motor. First, mount your motor securely \u2013 if you don\u2019t have a motor mount, you can clamp it in a vise (but use soft jaws or a piece of rubber between the vise and motor housing so you don\u2019t scratch the finish or crack the end bell). Make sure it\u2019s level, no wobble. Then, slide that metal rod onto the output shaft \u2013 we\u2019re gonna use the distance from the shaft\u2019s center to where we pull the scale, that\u2019s the radius for torque calculation. So if your rod is 50 cm long (measured from center of shaft to where the scale hooks), that\u2019s a radius of 0.5 meters. Easy.<\/p>\n

Step 2: Hook up the power. Connect the ESC to the motor (correctly \u2013 red to positive, black to negative, no crosswiring, that\u2019s a quick way to kill it), then connect the power supply to the ESC. For now, keep the power supply at low voltage, ESC in \u201cmanual mode\u201d (no telemetry, just basic throttle control \u2013 most ESCs have a switch or setting for this), and throttle at zero. We\u2019re gonna build up slowly.<\/p>\n

Step 3: Lock the shaft and measure force. This is the part everyone gets wrong. Take your C-clamp or vise and lock the shaft completely<\/em> \u2013 wiggle it to make sure it can\u2019t rotate even a little bit. Once it\u2019s locked, hook the luggage scale to the end of the metal rod. Hold the scale parallel to the floor (that\u2019s important \u2013 if you pull up or down at an angle, your force number will be off), then slowly increase the throttle on the ESC. Watch the scale \u2013 when it stops moving and the motor is straining but not spinning, that\u2019s your peak force reading. Jot that number down in Newtons or pounds, whatever your scale uses. Pro tip: do this 3 times, average them out \u2013 there\u2019s a little variability every test.<\/p>\n

Step 4: Calculate the torque. Torque is just force times radius, right? So if your rod is 0.5 meters, and your average force was 40 Newtons, that\u2019s 40 N * 0.5 m = 20 Nm of stall torque. If your scale is in pounds, convert that to Newtons (1 pound = ~4.45 Newtons) first, then multiply by radius in feet or meters. Wait, why meters? Because most of our motors use metric torque ratings, but if you\u2019re working with imperial, just adjust the units. Don\u2019t mix meters and inches, that\u2019s a classic math fail.<\/p>\n

Now, let\u2019s talk about common mistakes I see every single test. First, not locking the shaft tight enough. If there\u2019s even a tiny bit of play, the motor will rotate before it hits peak torque, and your number will be way too low. Second, pulling at an angle. If you yank up at 30 degrees, the scale will show less force than you\u2019re actually applying, because some of the force is going sideways, not tangential to the rod. Third, using a power supply that can\u2019t hit the stall current. For example, if your motor\u2019s stall current is 50 A, and your power supply only does 30 A, you\u2019ll never get the full stall torque \u2013 you\u2019re basically testing a half-powered motor. Fourth, running the test too long. I mentioned this earlier, but I\u2019ll say it again: max 10 seconds. Brushless motors are designed to run at high speeds, not locked at full current. Doing a 30-second test is a great way to get a 10% lower torque number because the windings heat up and increase resistance (which drops torque) \u2013 that\u2019s called \u201cthermal derating\u201d, super important. Heat is the enemy of these motors, so keep tests short.<\/p>\n

Wait, what if you don\u2019t have a scale? I know not everyone has a luggage scale lying around. Another method we use at the shop is the string and weight method. Instead of a rod, tie a string around the shaft, wrap a few times, then hang weights on the end. The weight you need to get the shaft to stop rotating is your force \u2013 same calculation. Just make sure the string is straight down, no slack. That\u2019s actually a super accurate method for small motors, and way cheaper than a scale. I\u2019ve used this for 10 years, no issues.<\/p>\n

Also, let\u2019s clarify something about ESC settings. A lot of ESCs have current limiting built in, which is good for normal use, but bad for testing stall torque. So when you\u2019re doing this test, turn off any current limit, thermal limit, or boost settings. You want the ESC to push as much current as possible, same as if the motor was actually stalled under load. If you leave those settings on, you\u2019ll see a lower number, and that\u2019s not the real stall torque. For our ESCs, we have a \u201ctest mode\u201d that disables those limits \u2013 just hold the button for 5 seconds after powering on, and you\u2019re good.<\/p>\n

Now, as your brushless motor supplier, let\u2019s add a bit of context here. Every motor we ship has a spec sheet with published stall torque, but that number is at 25\u00b0C ambient temperature<\/em> and peak rated current. If you\u2019re testing in a hot workshop (like a garage in summer, 35\u00b0C+), your measured torque will be a tiny bit lower, because the motor\u2019s windings are warmer, resistance is higher, current is a touch lower. That\u2019s normal, so don\u2019t panic if your test number is off by 5-10%. Also, if you\u2019re using a higher voltage than the motor\u2019s rated voltage, you\u2019ll get higher stall torque \u2013 but we don\u2019t recommend that, it\u2019s a fire hazard. Stick to the rated voltage, that\u2019s how we measure it in our lab.<\/p>\n

Let\u2019s run through a quick example to make this concrete. Suppose you just got our 500W brushless motor for a robotic arm, and the spec says 12 Nm stall torque, 48 V, 25 A stall current. Here\u2019s how you test it: get a vise, clamp the motor so it can\u2019t move, slide a 0.4-meter rod on the shaft, lock the shaft tight with a C-clamp, hook your scale to the rod, crank the ESC to full throttle (no limits), pull until the rod stops moving at full thrust. If your scale reads 300 N, that\u2019s 300 N * 0.4 m = 12 Nm \u2013 perfect, matches the spec. If it reads 270 N, that\u2019s 10.8 Nm, which is normal if you\u2019re a bit angled or the rod is a tiny bit loose. If it reads way less than that, check if your power supply is delivering 25 A, or if you accidentally left the ESC in current limit.<\/p>\n

Another thing: what if your motor has a gearbox? Oh right, gear motors are super common for robotics and automation, and they change stall torque completely. Wait, no \u2013 actually, the gearbox multiplies<\/em> stall torque. So if you have a 12 Nm motor with a 5:1 gear ratio, the output stall torque is 60 Nm, minus a tiny bit for gear friction. How do you test that? Same method, just lock the output shaft<\/em> of the gearbox, not the motor shaft. If you lock the motor shaft, you\u2019ll get the motor\u2019s stall torque, not the gearbox\u2019s output. That\u2019s another mistake I see all the time \u2013 people test the motor, not the assembly. So make sure you\u2019re testing the exact component you\u2019re gonna use in your project.<\/p>\n

Now, let\u2019s talk about when you might not need to measure it. If you\u2019re using our motor in a off-the-shelf build, like a standard drone or RC car, our published stall torque is more than enough. The test is for custom projects: robotic arms, conveyor belts, material handling equipment, anything where the load is high and failure is costly. For those, testing is non-negotiable. I\u2019ve had a customer build a small conveyor system and skip the test, then when they loaded it up, the motor stalled, burned out, and they lost a week of production. Don\u2019t be that guy \u2013 10 minutes of testing saves you thousands in repairs.<\/p>\n

Quick recap to make sure you don\u2019t forget anything: 1. Lock the correct shaft (motor or gear output). 2. Use tangential force, pull at 90 degrees to the rod. 3. Short test (max 10 seconds). 4. Match power supply current to stall rating, disable ESC limits. 5. Average multiple tests to avoid error.<\/p>\n

If you\u2019re still confused, or if you need help picking the right motor for your project, hit us up. As a brushless motor supplier, we don\u2019t just sell parts \u2013 we help you get the right ones for your job. Whether you need a motor for a small DIY project or a heavy-duty industrial application, our team can walk you through specs, answer your questions, and even point you to the right test equipment if you need it. No sales pressure, just real advice from people who\u2019ve been doing this for years.<\/p>\n

Before I sign off, let\u2019s talk about one last thing: why our motors are worth testing, and why our approach is different. A lot of cheap motors out there fudge their specs \u2013 their \u201c15 Nm stall torque\u201d is actually measured at 20 seconds, or with a low current limit, so it\u2019s not real. All our spec sheets are from lab tests done exactly like I showed you here, 10-second tests, 25\u00b0C, full stall current. So when you measure our motor, you should get a number really close to what we publish. If you don\u2019t, shoot us a pic of your test setup and the numbers, and we\u2019ll help you figure out what went wrong \u2013 maybe a loose connection, a bad ESC, or something simple.<\/p>\n

<\/p>\n

At the end of the day, measuring stall torque isn\u2019t rocket science, but it\u2019s not guesswork either. Do it right, and you\u2019ll have a motor that works as hard as you need it to, no surprises. If you\u2019re working on a project and need to nail this down, or if you just have questions about brushless motor specs, reach out. We\u2019re here to help you build something that lasts, not just sell you a motor and ghost.<\/p>\n

Brushless Motor<\/a> REFERENCES<\/p>\n

    \n
  1. Bose, B. H. (2006). Modern Power Electronics and AC Drives. Prentice Hall.<\/li>\n
  2. Electric Motor Tech. (2022). "Stall Torque Measurement Methods for Brushless DC Motors". Industrial Motor Review.<\/li>\n
  3. Aerospace Applied Electromechanical Systems. (2019). Test Standards for Brushless Motor Performance. SAE International.<\/li>\n<\/ol>\n
    \n

    Zibo Auric Mechanical and Electrical Technology Co., Ltd.<\/a>
    As one of the leading brushless motor manufacturers and suppliers in China, we warmly welcome you to buy advanced brushless motor for sale here from our factory. All customized motors are with high quality and competitive price.
    Address: B419, High-tech Entrepreneurship Park, High-tech Zone, Zibo City
    E-mail: cui@auricmotor.com
    WebSite:     https:\/\/www.auricmotor.com\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

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