In automation equipment, mobile robots, and industrial machinery, motor selection is not only about checking whether the motor can provide enough torque.

Many engineers calculate torque first to confirm whether the motor can drive the load. However, torque alone cannot fully determine whether a motor is suitable for the application.

In real projects, a machine may start normally and move the load successfully, but problems can occur when it reaches the target speed, such as excessive temperature rise, insufficient continuous output, or overload alarms.

In many cases, the problem is not incorrect torque calculation, but insufficient power verification.

Torque determines whether the motor has enough force to move the load, while power determines whether the motor can continuously deliver the required output at the target speed.

For example, the same torque value of 2 N.m requires completely different power levels at 100 rpm and 3000 rpm.

Therefore, after calculating torque, engineers also need to calculate motor power to verify whether the motor can meet the actual working conditions.

1. Relationship Between Motor Power, Torque, and Speed

Motor output can be understood through three important parameters:

Torque represents the rotational force generated by the motor and determines whether the motor can drive the load.

Speed represents how fast the motor rotates and determines the movement speed of the equipment.

Power represents the mechanical energy that the motor can deliver within a certain period of time.

A simple example is riding a bicycle.

When riding uphill, more force is required to push the pedals, but the speed is usually lower.

When riding at high speed on flat ground, the pedaling force may be smaller, but the legs rotate faster and the total energy output increases.

The same principle applies to motors.

A motor with enough torque does not always have enough capability for high-speed operation.

Only by considering torque and speed together can the actual motor performance be evaluated.

2. How to Calculate Motor Power

The basic relationship between power, torque, and speed is:

Motor Power = Torque x Angular Speed

In engineering applications, motor speed is usually expressed in rpm, so the commonly used formula is:

Motor Power kW = Torque N.m x Speed rpm / 9550

For power calculation in watts:

Motor Power W = Torque N.m x Speed rpm / 9.55

This formula shows that motor power depends on both torque and speed.

Higher torque requires higher power.

Higher speed also requires higher power.

Therefore, when selecting a motor, engineers should not only check the torque value but also consider the operating speed corresponding to that torque.

Higher speed requires more power.

3. Why Higher Speed Needs More Power? Motor output depends on both torque and speed. When the motor rotates faster, it needs to deliver more energy in the same amount of time. Therefore, a higher running speed usually requires a higher power level. This is why some equipment works normally at a low speed but cannot maintain the same performance when the speed increases. In many cases, the problem is not the lack of torque. The real issue is that the motor cannot provide enough power for continuous operation at the target speed.

4. How to Calculate Power for Linear Motion Systems

Many automation systems use linear motion mechanisms, such as:

• Ball screw systems

• Linear modules

• Lifting mechanisms

• Material handling equipment

For these applications, the required parameters are usually:

• Thrust force

• Moving speed

• Transmission efficiency

The calculation method is:

Motor Power = Force x Speed / Efficiency

For example:

Thrust force: 400 N

Speed: 500 mm/s

Ball screw efficiency: 0.9

Convert speed:

500 mm/s = 0.5 m/s

Calculation:

Motor Power = 400 x 0.5 / 0.9

The result is approximately 222 W.

This means the mechanism requires about 222 W mechanical output power under this working condition.

When converting the requirement to the motor shaft, the same principle applies.

Linear force x Linear speed equals Rotational torque x Motor speed.