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

Many engineers start with torque calculation to determine whether the motor can drive the load. However, torque alone does not fully determine whether a motor is suitable for the application.

In real projects, a machine may start normally and move the load successfully, but after reaching the target speed, the motor may experience excessive temperature rise, insufficient continuous output, or overload alarms.

The reason is often not an 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 2N.m torque requires completely different power levels at 100rpm and 3000rpm. Therefore, after torque calculation, motor power calculation is also necessary to verify whether the motor can meet the actual operating requirements.

1. Why Torque Alone Is Not Enough for Motor Selection

Motor output can be understood from three key factors: torque, speed, and power.

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 combines torque and speed, representing how much mechanical energy the motor can deliver within a certain period of time.

A bicycle provides a simple example.

When riding uphill, a rider needs to apply greater force to the pedals, but the riding speed is usually lower. When riding at high speed on flat ground, the pedaling force may be lower, but the legs rotate faster and the total energy output increases.

If high speed and climbing ability are required at the same time, the required power becomes much higher.

The same principle applies to industrial motors.

A motor with sufficient torque does not necessarily have enough capability for high-speed operation. Only by considering both torque and speed can the actual output capability be evaluated.

2. How to Calculate Motor Power?

Mechanical power is determined by torque and rotational speed.

The commonly used engineering calculation method is:

Motor Power = Torque x Speed / 9550

The calculation result represents the mechanical output power of the motor.

This relationship 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 whether the torque is sufficient but also confirm whether the motor can maintain the required output at the target speed.

3. Why Does Higher Speed Require More Power at the Same Torque?

Assume a motor provides the same torque output under different operating speeds.

At a lower speed, the motor requires relatively less power.

When the rotation speed increases significantly, the motor needs to deliver more energy within the same period of time, which means the required power increases accordingly.

This explains why some machines can operate normally at low speed but experience insufficient output capability or excessive heating when running faster.

In many applications, the limitation is not insufficient torque. The actual issue is that the motor cannot provide enough continuous power under the required operating speed.

4. How to Calculate Power for Linear Motion Systems?

Many automation systems use linear motion mechanisms, such as:

Ball screw actuators

Linear modules

Lifting mechanisms

Material handling systems

For these applications, power requirements are mainly determined by:

Thrust force

Moving speed

Transmission efficiency

The basic relationship is:

Motor Power = Force x Speed / Efficiency

For example, if a linear mechanism requires a certain thrust force and moves at a certain speed, the required mechanical power can be calculated based on the load condition and transmission efficiency.

When converting the requirement to the motor shaft, factors such as screw lead, reduction ratio, and mechanical efficiency should also be considered.

Whether the application is linear motion or rotary motion, the principle remains the same:

The required power depends on how much force is needed and how fast the movement must be completed.

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5. Why Must Transmission Efficiency Be Considered?

In real mechanical systems, motor energy cannot be transferred to the load with 100 percent efficiency.

Energy losses may occur through:

Ball screw friction

Gear reducer losses

Belt transmission losses

Bearing friction

Guide rail resistance

Therefore, motor selection must consider the complete transmission system rather than only the load requirement.

A lower transmission efficiency means the motor needs to provide higher output power to achieve the same load performance.

This is why the same application may require different motor specifications when different mechanical structures are used.

6. Motor Power Selection Requires Torque-Speed Curve Analysis

The rated power shown in a motor datasheet is only one reference parameter.

To determine whether a motor is suitable, engineers should also analyze the torque-speed curve.

Different working conditions require attention to different performance factors:

Low-speed operation:

Focus on continuous torque capability.

High-speed operation:

Focus on continuous power output.

Acceleration and deceleration:

Focus on peak torque capability and drive performance.

Long-term operation:

Focus on temperature rise and thermal capacity.

Some motors provide strong torque at low speed but lose output capability at higher speed.

Some motors can deliver high peak performance but cannot maintain continuous operation under heavy load.

Therefore, motor power calculation is not simply about selecting a larger power rating. It is about confirming whether the motor can operate reliably under actual working conditions.

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7. Motor Power Calculation Is Only One Part of Motor Selection

Power calculation is an important step, but it is not the final step in motor selection.

After determining the required power, engineers still need to verify:

Whether peak torque meets acceleration requirements

Whether continuous operation causes excessive heating

Whether transmission efficiency has been considered

Whether vertical loads require holding torque or braking

Whether frequent start-stop cycles exist

A reliable motor selection process should consider multiple factors, including load characteristics, inertia, torque requirements, power demand, and actual operating conditions.

8. Three Steps for Motor Power Calculation

In practical engineering projects, motor power calculation can be completed through three steps.

Step 1: Determine Load Requirements

Analyze:

Load force

Required torque

Operating speed

Working cycle

Step 2: Convert Requirements to Motor Parameters

Consider:

Gear ratio

Screw lead

Transmission efficiency

Then determine:

Motor output torque

Motor operating speed

Step 3: Verify Motor Performance

Check:

Rated power

Continuous torque

Peak torque

Maximum speed

Temperature rise

Only after these parameters are verified can the motor be confirmed suitable for the application.

9. Five Common Mistakes in Motor Power Calculation

Mistake 1: Looking Only at Power and Ignoring Torque

Motors with the same power rating may provide different torque output under different operating conditions. Low-speed heavy-load applications cannot be selected based only on power.

Mistake 2: Looking Only at Torque and Ignoring Speed

A motor may have enough torque to move the load but still fail to achieve the required operating speed.

Mistake 3: Ignoring Transmission Efficiency

The power required by the load is not equal to the actual motor output requirement. Mechanical losses must be considered.

Mistake 4: Treating Peak Power as Continuous Power

Peak performance only represents short-term capability. Long-term operation depends on rated performance and thermal capacity.

Mistake 5: Checking Only Datasheet Values Without Performance Curves

A motor should be evaluated according to its complete torque-speed characteristics, not just one rated parameter.

Summary: The Core Logic of Motor Power Calculation

Motor power calculation is an essential part of reliable motor selection.

The basic principle is:

Torque determines whether the motor can move the load.

Speed determines how fast the equipment can operate.

Power determines whether the motor can continuously deliver the required output at the target speed.

A complete motor selection process should include:

Load analysis

Torque calculation

Power verification

Performance curve analysis

Working condition evaluation

For mobile robot applications, including AGV drive wheels, AMR drive systems, and low-voltage servo drive solutions, Plutools focuses on complete drive system matching rather than selecting components based on a single parameter.

Through professional engineering analysis and system verification, Plutools helps customers achieve higher efficiency, improved reliability, and longer service life for intelligent mobile equipment.

Engineering rule of thumb:

Low speed: Focus on torque.

High speed: Focus on power.

Continuous operation: Focus on heat generation.

Final motor selection should always be based on complete working conditions and motor performance verification.