How to Calculate the Required Motor Torque

Who this guide is for

Engineering buyers, shutter manufacturers, installers, project contractors and distributors use this page to make one buying decision clearer before requesting price, samples or OEM support.

The page is intentionally written as a procurement guide. It does not replace product datasheets, local electrical rules, final system testing or installer responsibility.

What torque means for tubular motors

Torque is the turning force the motor applies to the tube. In a shutter, blind or awning system, the motor must rotate the tube while lifting or moving the load. The basic calculation depends on the load and the effective radius of the tube, but the procurement decision must also consider friction, balance, installation resistance and how often the system runs.

For simple early estimation, buyers often start with load multiplied by tube radius. This gives a useful starting point, but it is not a final project guarantee. Real systems have guide rails, bearings, fabric tension, slat friction, wind influence and installation tolerances. A supplier recommendation should therefore include a margin and sample testing.

The required torque changes when tube diameter changes. A heavier curtain on a smaller tube can sometimes need less torque than the same curtain on a larger tube, because torque is related to radius. This is why a quote request should include tube size rather than only curtain weight.

Data needed before calculation

The buyer should collect curtain or fabric weight, finished width, finished height, tube diameter, slat or fabric type, guide rail condition, bearing condition, installation angle and desired control method. For roller shutters, the slat material and side guide friction can strongly affect performance. For awnings, arm tension and outdoor conditions matter. For blinds, fabric rolling behavior and noise expectation matter.

When the exact weight is not available, estimate it from material data and size, then validate with a sample. For repeat orders, use the previous tested configuration as a reference, but still confirm if the tube, slat, supplier or installation method has changed. Small changes in the complete system can change the working load.

Voltage stability also matters. A motor selected at the edge of its capacity can behave poorly when site voltage drops or when friction increases over time. Professional buyers normally prefer a reasonable torque margin rather than a motor that only works in perfect conditions.

Adding a practical safety margin

A safety margin is used because the installed system rarely behaves exactly like a clean calculation. Friction, tube deformation, curtain alignment, weather, installation quality and user behavior can all increase the working load. A margin helps the motor start reliably and avoid repeated thermal protection in normal use.

The margin should be practical, not excessive. Oversizing every project can create higher cost, larger motor heads, compatibility problems and unnecessary stock pressure. The right margin depends on application risk. A commercial shutter with heavy daily use deserves more conservative selection than a light indoor shade.

Walter can help compare a calculated requirement against available motor series and torque options. The buyer should ask for the recommended model, alternative model, reason for selection and sample test plan. This makes the quotation easier to approve internally.

Common torque calculation mistakes

The first mistake is calculating from motor diameter instead of load and tube radius. A 45mm motor is not automatically correct for every 45mm tube application. Motor series, torque, speed, limit type and accessory package must all fit the job.

The second mistake is ignoring friction. A shutter that moves smoothly during a workshop test can become harder to lift after installation if the guide rails are tight, the curtain is not aligned or the bracket position is poor. Friction should be considered before bulk order approval.

The third mistake is treating higher torque as always better. Excessive torque can hide installation problems during testing and create stress in the system. For a professional buying program, correct torque plus clean installation is better than simply selecting the largest available motor.

• Confirm moving weight and tube diameter before quotation.
• Include guide rail or fabric tension conditions.
• Ask for a recommended motor and an alternative option.
• Test samples with the real tube and accessories.
• Record the approved configuration for repeat orders.

What to send Walter for torque selection

Send the application, width, height, tube diameter, tube drawing or photo, moving weight, voltage, control type, daily use estimate and any special site conditions. If the project uses existing shutters, send photos of the installed shutter, tube end, bracket and old motor label.

For large OEM orders, ask for a sample validation plan. A useful plan includes no-load test, load test, limit repeatability check, thermal behavior observation and accessory fit confirmation. These tests make the torque decision easier to defend before the first production order.

Torque Sample Test Checklist

The calculated torque is a starting point, not the final approval. The sample should be tested with the real curtain, shutter or fabric weight, the actual tube diameter and the guide rail or side channel that will be used in the field.

During testing, pay attention to the first movement from rest. A motor that can move the load after it is already travelling may still struggle at startup if friction is high.

• Test with the real curtain, shutter or fabric weight.
• Measure starting behavior from the fully closed position.
• Run the full travel height several times.
• Observe whether thermal protection is triggered.
• Record tube diameter, guide rail friction and installation angle.
• Compare the recommended torque with the next higher torque option.

Recommended Torque vs Next Torque Option

If the recommended model is close to the calculated limit, test one higher torque option before final approval. The higher option may reduce service risk, but it can also change speed, noise, cost, tube fit or available control features.

The buyer should document why the final torque was selected. That note is useful when a later project has a similar size but heavier material or less accurate installation.

Field Variables That Change Torque Demand

Torque demand changes when the tube supplier changes, when guide rails are narrow, when curtain slats rub against side channels, or when outdoor temperature affects material stiffness. These details explain why the same nominal size can behave differently in two projects.

For roller shutters, guide rail friction and curtain alignment are especially important. For blinds and screens, fabric tension, bottom bar weight and tube diameter can change the real torque requirement.

Torque RFQ Data Walter Needs

Send finished width and height, material weight, tube diameter, tube profile, installation type, expected daily cycles and target voltage. If the weight is unknown, send material details and photos so Walter can estimate more responsibly.

Avoid requesting only a motor diameter and price. For torque selection, missing load data usually creates either underpowered samples or unnecessarily expensive motors.

Related guide pages

Use these pages to complete the buying decision before requesting samples or a final quotation.

• Selection by Application
• Tube and Bracket Compatibility
• Limit Systems
• Manual Override
• Safety Protection