Calculator
Example Data Table
| Case | Load | Radius | Gear Ratio | Safety Factor | Estimated Need |
|---|---|---|---|---|---|
| Small lift axis | 5 kg | 0.04 m | 3:1 | 1.5 | About 121 N·cm |
| Rotary table | 8 kg | 0.08 m | 4:1 | 1.8 | Depends on inertia |
| Tilt arm | 3 kg | 0.18 m | 5:1 | 2.0 | Highest near horizontal |
Formula Used
Gravity torque: T = m × g × r × sin θ
Force torque: T = F × L × sin θ
Acceleration torque: T = J × α
Total load torque: Tload = Tgravity + Tforce + Taccel + Tfriction + Tpreload
Required motor holding torque: Tmotor = Tload × Safety Factor ÷ Gear Ratio ÷ Gear Efficiency
Available torque: Tavailable = Rated Torque × Current Factor × Derating Factors + Detent Torque
How to Use This Calculator
Enter the load type first. Use vertical lift for lead screws, pulleys, and hoists.
Enter mass and radius when the load is known. Use force mode when a measured external force is available.
Add friction, preload, inertia, and acceleration for a better estimate. These values help avoid undersized motors.
Enter gear ratio and efficiency. A higher gear ratio increases holding ability, but losses reduce useful torque.
Set the motor torque and driver current. The calculator estimates real available torque after current and derating effects.
Press the calculate button. Review the margin and status before choosing the motor.
Stepper Motor Holding Torque Guide
What Holding Torque Means
Holding torque is the maximum static torque a stepper motor can resist while energized. It matters when an axis must hold position without moving. A lift axis, rotary table, clamp, camera head, or indexer may need strong holding torque. The rating on a motor data sheet is usually measured at rated current. Real systems often deliver less torque. Driver current, heat, microstepping, wiring, and supply limits can reduce the useful value.
Why Load Torque Matters
A load creates torque when force acts at a radius. Vertical loads need more torque because gravity always pulls downward. Tilting arms are usually worst near the horizontal position. Rotary tables may have low gravity torque, yet high inertia torque. Fast acceleration can demand more torque than slow holding. Friction can also be helpful or harmful. It may resist motion, but it can increase the torque needed to start.
Using Safety Margin
A motor should not be selected at the exact calculated limit. Use a safety factor for unknown friction, shock, vibration, and load changes. Many simple machines use 1.5 as a starting value. Heavy lifts or vertical axes may need 2.0 or more. Backdriving risk should also be checked. A gearbox can increase holding torque. Yet gearbox efficiency reduces the final torque.
Driver Current and Derating
Holding torque is strongly linked to phase current. If the driver is set below rated current, torque drops. Microstepping can make motion smoother. It may reduce incremental holding strength at each microstep. Heat also changes motor behavior. Long holding periods can make the motor hot. Use temperature derating when the motor runs inside a cabinet.
Practical Selection Tips
Compare required torque with available motor torque. A positive margin means the estimate passes. A small margin is still risky in real machines. Increase motor size, increase gear ratio, reduce radius, or lower load. Test the final design under the heaviest load. Also check speed torque curves. Holding torque does not guarantee torque at high speed.
FAQs
What is stepper motor holding torque?
It is the static torque a powered stepper motor can resist while holding position. It is usually rated at full phase current.
Is holding torque the same as running torque?
No. Holding torque is measured at standstill. Running torque falls as speed rises because coil current has less time to build.
Why does gear efficiency affect required torque?
Gears multiply torque, but they also waste energy through friction. Lower efficiency means the motor must provide more input torque.
What safety factor should I use?
Use 1.5 for light predictable systems. Use 2.0 or higher for vertical loads, shocks, poor data, or safety critical machines.
Does microstepping reduce holding torque?
Full rated holding torque may still exist at full step positions. However, small microstep positions can have lower incremental stiffness.
Why include load inertia?
Inertia matters when the axis accelerates. High inertia can require extra torque even when gravity torque is small.
Can detent torque hold a load without power?
Detent torque is usually small. Do not rely on it for heavy vertical loads unless the design is mechanically safe.
What if the calculator shows fail?
Use a larger motor, increase gear ratio, reduce pulley radius, lower load, improve efficiency, or add a brake for vertical axes.