What Is Torque? How Robots Generate Turning Force.

What Is Torque?

Torque is the turning effect of a force applied around an axis.

In robotics, torque determines how strongly a motor or actuator can rotate a joint, wheel, or other mechanism.

For example, a robotic elbow must generate sufficient torque to lift and support the weight of the arm, gripper, and any object it carries.

Torque is commonly measured in newton-meters (N·m).

It is one of the most important specifications when selecting motors and robotic joint actuators.

Key Takeaways

• Torque measures the rotational effect of an applied force.
• Torque depends on the force and its perpendicular distance from the rotation axis.
• Available torque varies with motor speed, gearing, temperature, and operating conditions.

How Is Torque Calculated?

For a force applied perpendicular to a lever arm:

Torque = Force × Perpendicular Distance

Suppose a force of 40 newtons is applied 0.25 meters from a rotation axis.

The resulting torque is:

40 × 0.25 = 10 N·m

If the same force is applied farther from the axis, the turning effect increases.

More generally, torque depends on the angle between the position vector and the force.

This relationship explains why a robot's payload position matters.

How Does Torque Affect a Robot Arm?

Imagine a robot holding a 5-kilogram object.

The object's weight creates a force due to gravity.

When the arm extends horizontally, the weight acts at a distance from the supporting joints.

Those joints must generate torque to resist gravity.

If the robot moves the object farther from its base, the required torque at certain joints can increase.

Acceleration can also create additional torque demands.

Therefore, a robot's payload capability depends on the configuration and motion, not just the object's mass.

Torque vs. Force

Force can cause linear acceleration or deformation.

Torque produces a turning effect.

For example, a gripper may apply force to squeeze an object.

A joint motor produces torque to rotate the arm.

The two are related through geometry, and a motor's torque can be converted into linear force using appropriate mechanical mechanisms.

However, a torque rating and a force rating should not be compared as though they describe the same quantity.

Torque vs. Power

Torque describes the turning effect.

Mechanical power describes the rate at which mechanical work is performed.

For a rotating shaft:

Power = Torque × Angular Velocity

A motor can generate substantial torque at low speed while producing relatively little mechanical power.

Conversely, a motor producing moderate torque at high speed can deliver substantial power.

Both torque and speed matter when evaluating an actuator.

How Does a Gearbox Affect Torque?

A reduction gearbox decreases output speed while increasing output torque, subject to losses.

For example, a 10:1 reduction gearbox provides an ideal torque multiplication of ten.

If the input torque is 2 N·m, ideal output torque would be 20 N·m.

Real gearboxes experience losses, so actual output is lower.

A gearbox does not create additional mechanical power.

It trades rotational speed for torque.

Continuous vs. Peak Torque

Continuous torque: The torque a motor or actuator can sustain under specified operating and thermal conditions.

Peak torque: A higher torque available for a limited period under defined conditions.

For example, a robot joint may briefly need extra torque during acceleration.

However, using peak torque continuously can overheat equipment or exceed its ratings.

Engineers therefore evaluate duty cycles and thermal limits.

Frequently Asked Questions

Does more torque always mean a robot can lift more?

Not necessarily. Payload depends on joint geometry, other actuators, structural limits, and operating requirements.

Is torque the same as motor speed?

No. Torque describes turning effect, while speed describes rotation rate.

The Bottom Line

Torque describes a motor's ability to generate turning force. In robotics, it must be evaluated alongside joint geometry, speed, gearing, payload, and thermal performance.