As a servo drives supplier, I’ve spent the last seven years sitting across conference tables, walking factory floors, and troubleshooting startup glitches with engineers who keep asking the same core question: “How much torque do I actually need?” It’s a question that’s not as simple as it sounds—too little torque and your line stalls mid-cycle, too much and you’re wasting energy, overspending on hardware, and adding unnecessary wear to every component on the machine. Over time, I’ve learned that torque requirements aren’t one-size-fits-all; they shift wildly depending on what the servo is doing, what it’s moving, and how fast it needs to get there. Today, I want to break down the real-world torque needs across the most common servo drive applications, the math that matters (without making your eyes glaze over), and the mistakes I see engineers make every single day. Servo Drives
Let’s start with the basics that no sales sheet will fully explain: torque in servo drives has two main components. There’s continuous torque—this is the steady, low-grade force a motor needs to keep moving a load consistently, hour after hour, without overheating. Then there’s peak torque: the short burst of power needed to accelerate a load from a dead stop, decelerate it quickly, or overcome a sudden resistance like a jammed conveyor or a heavy payload. Most engineers get this, but what they mess up is adding a safety factor that’s either too tight (and leads to repeated failures) or way too loose (and blows their budget). I always tell them: if your cycle is ten minutes long, the peak torque only lasts two seconds, so you don’t need a motor that’s sized for that two-second burst to run 24/7. That’s where I see 30% of over-sizing errors happen.
First up: packaging and labelling machinery. This is one of the most demanding applications for servo drives, and it’s where torque calculations feel like a balancing act. Think about a blister pack line for pharmaceuticals: you have a rotary index table that moves blister cards into sealing stations, a pick-and-place arm that drops pills into the blisters, a sealing head that presses down, and a labelling wheel that applies stickers before the boxer grabs the finished packs. Each of these axes has different torque needs, and if even one is off, the whole line slows down. For small to mid-sized packaging machines, we typically see continuous torque requirements between 0.5 Nm and 5 Nm, with peak torque hitting 2 Nm to 15 Nm. The reason peak torque is so high here is acceleration: index tables have to move 100+ kg of metal and product around a 1-meter diameter circle in less than 0.5 seconds. Add in the occasional sudden stop if a misfeed triggers a safety stop, and that peak torque number jumps fast. I remember a project a couple years back with a medical packaging customer who tried to cut costs by going with a 3 Nm peak torque motor for their index table, instead of the 8 Nm we recommended. Three months in, they were replacing belts and bearings every two weeks because the under-sized motor couldn’t handle the repeated acceleration, leading to excess vibration that wore out every component on the axis. That’s the kind of mistake we solve every day.
Next: industrial robotics, specifically the articulated and delta robots that are the backbone of modern warehouses and manufacturing lines. Servo drives here aren’t just moving a simple table—they’re moving a robotic arm that can weigh 50 kg empty and hold 20 kg payloads, all while repeating the same motion 10,000 times a day. Torque requirements here are split across the robot’s joints, and they change dramatically based on the robot’s configuration. A small delta robot used for picking small parts (like electronics components) will have joint torque as low as 0.1 Nm for the shoulder and elbow, going up to 2 Nm at the end effector that grabs parts. But a heavy-payload articulated robot used for welding automotive frames? We’re talking continuous torque of 20 Nm to 100 Nm on the large shoulder joint, with peak torque spiking to 300 Nm or more when the arm swings a 50 kg payload from one side of a car chassis to the other. What’s unique about robotics is that torque is dynamic—it’s not just about moving weight, it’s about the lever arm. A robot’s elbow joint, for example, has to exert more torque when the arm is fully extended than when it’s tucked in, even if the payload is the same. I always work with robot integrators here to map each joint’s torque curve across its entire range of motion, because a lot of cheaper servo drives can’t adjust torque in real time as the arm moves. That leads to jerky motion, reduced payload capacity, and shorter robot life.
Third on the list: CNC machining and metalworking. This is where servo torque has to deal with not just moving parts, but cutting through hard metal—so you have to account for both axis torque and cutting load torque. CNC machines have three main axes: X, Y, Z, and sometimes a rotary axis for turning parts. The X and Y axes, which move the cutting table, usually have continuous torque between 1 Nm and 10 Nm, with peak torque up to 25 Nm. The Z axis, which lowers the cutting tool into the workpiece, has to handle both the weight of the tool and the downward force of cutting, so its continuous torque is higher—often 5 Nm to 20 Nm, peak torque reaching 50 Nm or more. The big variable here is the material being cut: a CNC mill cutting aluminum will need less torque than one cutting hardened steel, and a lathe turning a 300 mm steel bar will need way more torque than one turning a small aluminum part. I’ve seen customers swap from aluminum to titanium parts and forget to adjust their servo drive sizing, leading to stalled cutters, broken tools, and damaged workpieces. Another quirk of CNC is that constant torque isn’t enough—you need servo drives that can provide consistent torque even at low speeds, because the cutting tool is moving at a fraction of a meter per minute when it’s doing heavy cuts. A lot of cheap servo drives drop torque at low speeds, which is a dealbreaker here.
Then there’s the less obvious application: material handling, specifically conveyors and automated guided vehicles (AGVs). This is where torque requirements are deceptively simple, but still often mis-sized. A flat conveyor moving boxes across a warehouse floor only needs torque to overcome friction and accelerate the load. For a small conveyor moving 50 kg boxes, continuous torque might be 1 Nm to 3 Nm, peak torque 5 Nm to 8 Nm. But AGVs are a different story: they’re mobile, so they have to handle not just their own weight, but payloads up to several tons, plus uneven floor surfaces, and the turning force of steering wheels. A standard AGV moving pallets will have wheel torque of 10 Nm to 50 Nm continuous, peak torque up to 150 Nm when accelerating or climbing a slight ramp. Where I see mistakes here is not accounting for inertia. When a conveyor is carrying a continuous load, inertia is lower, but when an AGV has to stop suddenly to avoid a person or a fallen pallet, the inertia of a 1,000 kg load creates a huge torque spike. Last year we worked with a logistics company that installed under-sized servo drives on their AGV fleet—over six months, half the AGVs’ motors burned out because they couldn’t handle the repeated emergency stops. We upgraded their drives to handle 2x more peak torque, and that failure rate dropped to zero.
Another growing application is additive manufacturing, or 3D printing for industrial parts. This is a mix of high-speed motion and precise force, so torque requirements are more specialized than other applications. FDM (fused deposition modeling) printers have X and Y axes that move the print head, with continuous torque of 0.2 Nm to 1 Nm, peak torque up to 3 Nm. But SLA (stereolithography) printers, which use resin and require the build plate to move with high precision, have slightly higher torque, around 1 Nm to 3 Nm continuous. The big difference in additive manufacturing is that torque has to be extremely consistent because any fluctuation leads to layer shifting, ruining a $1,000+ part. A lot of new 3D printer manufacturers skimp on servo drives to cut costs, and the result is a 50% failure rate on first-run parts. We’ve developed a line of compact, high-torque-density servo drives specifically for additive manufacturing that solve this exact problem.
Now, let’s talk about the math that ties all this together, because you don’t have to be an engineer to get it right. The basic formula for required continuous torque is T = (F * d) / (2 * π * η), where F is the force needed to move the load, d is the diameter of the drive wheel or pulley, and η is the efficiency of the mechanical system (usually 0.8 to 0.9 for most setups). For peak torque, you have to add acceleration torque, which is T_accel = (J * α), where J is the moment of inertia of the load and α is the angular acceleration. The biggest mistake I see here is ignoring inertia—both of the load and the motor itself. When you have a long axis, like a conveyor or a robot arm, the inertia of the load is way higher than the motor’s inertia, so you have to size the motor to handle that combined inertia. If the motor’s inertia is too small, you’ll get sluggish motion, or worse, the motor will stall because it can’t overcome the load’s inertia.
I also want to address common myths I hear from engineers all the time. First myth: “Higher torque is always better.” No—higher torque usually means a bigger, heavier, more expensive motor, and if you don’t need it, you’re wasting money and adding unnecessary weight to the machine, which increases inertia and actually makes performance worse. Second myth: “Continuous torque is the only number that matters.” Peak torque is what handles 90% of dynamic loads, so if you size only for continuous torque, you’ll have constant failures. Third myth: “All servo drives have the same torque output.” That’s not true—some drives are rated at 25°C, and their torque drops by 20% when operating at 40°C in a hot factory, which is standard. You have to adjust for operating temperature, altitude, and any other environmental factors, like dust or moisture, that can affect performance.
At the end of the day, getting torque requirements right is about understanding your specific application’s cycle, load, and environment. Every machine is different, so there’s no universal formula, but there are patterns that we’ve honed over years of working with customers across industries. If you’re currently designing a new line, upgrading an old machine, or troubleshooting repeated servo failures, our team can help you calculate the exact torque needs for your axes, size the right servo drives, and avoid the mistakes that cost thousands in downtime and replacements. We don’t do one-size-fits-all solutions—we work with you to match the drive to your application, not the other way around. If you’re ready to stop guessing at torque requirements and start getting consistent, reliable performance from your servo systems, reach out to our team to discuss your project.
AC Servo Drive References:
- Bolton, W. (2017). Electrical Machines and Drives. Routledge.
- Krishnan, R. (2010). Electric Motor Drives: Modeling, Analysis, and Control. Prentice Hall.
- American National Standards Institute. (2020). ANSI/B95.5-2020: Safety of Industrial Robots and Robot Systems.
- Load Calculation Handbook for Industrial Servo Drives. (2022). Motion Control Association.
- CNC Machining Fundamentals. (2021). Society of Manufacturing Engineers.
TOMATECH Technology Co., Ltd.
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