{"id":7583,"date":"2026-09-18T16:49:16","date_gmt":"2026-09-18T16:49:16","guid":{"rendered":"https:\/\/faradyi.com\/?p=7583"},"modified":"2026-09-18T16:49:27","modified_gmt":"2026-09-18T16:49:27","slug":"brushless-dc-motor-torque-how-to-increase-it-safely","status":"publish","type":"post","link":"https:\/\/faradyi.com\/ar\/brushless-dc-motor-torque-how-to-increase-it-safely\/","title":{"rendered":"Brushless DC Motor Torque: How to Increase It Safely"},"content":{"rendered":"
\n\t\t\t\t
\n\t\t\t\t\t
\n\t\t\t\t
\n\t\t\t\t
\n\t\t\t\t\t\t\t\t\t

Brushless DC motor torque is determined primarily by the motor\u2019s torque constant and the phase current supplied by the controller. More current can produce more torque within the motor\u2019s linear operating region, but current also raises winding losses and temperature. The practical goal is therefore not simply to \u201cincrease stall torque.\u201d It is to deliver the required continuous and peak torque at the target speed, for the required duty cycle, without exceeding the motor, controller, connector, gearbox, or thermal limits.<\/p>

Quick answer:<\/strong> To increase usable BLDC torque, first confirm the current limit and current measurement, improve commutation or field-oriented control, reduce avoidable mechanical losses, and improve the thermal path. If the application still needs more torque, use suitable gear reduction or select a motor with a higher torque constant, larger active volume, or greater continuous thermal capacity. Never raise current or voltage beyond documented motor and drive limits.<\/p><\/div>

Safety note:<\/strong> A stalled motor has zero shaft speed and therefore produces zero mechanical output power, even though it may draw high current and create substantial heat. Do not perform a locked-rotor test unless the motor manufacturer\u2019s procedure, current limit, temperature monitoring, fixture, and maximum test duration are known.<\/p>

What Determines Brushless DC Motor Torque?<\/h2>

In the normal unsaturated operating region, electromagnetic torque can be approximated as:<\/p>

Torque \u2248 torque constant (Kt<\/sub>) \u00d7 torque-producing current<\/strong><\/p>

The simple relationship is useful, but it must be applied with the same current convention used in the motor datasheet and controller. Peak versus RMS current, phase versus line current, and trapezoidal versus sinusoidal commutation can change the numerical comparison. Winding temperature, magnetic saturation, commutation angle, rotor position, and mechanical friction also affect measured shaft torque.<\/p>

Torque constant and winding choice<\/h3>

A higher Kt<\/sub> produces more torque per ampere, but winding changes are not a free performance gain. More turns generally increase torque constant and reduce speed constant, while also changing resistance, inductance, current response, and voltage requirements. Compare candidate windings at the required operating point\u2014not from Kt<\/sub> alone.<\/p>

Current, copper loss, and temperature<\/h3>

Current creates torque, but winding copper loss rises approximately with current squared (I\u00b2R). Doubling current can therefore create roughly four times the resistive loss at the same winding resistance. Resistance also increases as copper heats, so voltage-controlled systems may produce less current and torque as the winding temperature rises. Thermal limits often determine continuous torque before the magnetic or mechanical limit is reached.<\/p>

Speed and available bus voltage<\/h3>

At higher speed, back electromotive force (back EMF) consumes more of the available bus voltage. The controller then has less voltage headroom to force the commanded current through winding resistance and inductance. A suitable bus voltage can help maintain torque at speed, but at zero speed an adequately regulating current controller\u2014not voltage alone\u2014sets torque.<\/p>

<\/p>

\"CutawayBLDC torque comes from controlled winding current, while the motor housing and mounting path must remove the resulting heat.<\/figcaption><\/figure>

Stall Torque vs. Peak and Continuous Torque<\/h2>

These torque values are not interchangeable. When comparing motors, check the test conditions and duration behind each rating.<\/p>

On a phone, swipe horizontally to view the complete table.<\/em><\/p>

Torque term<\/th>What it means<\/th>Primary limit<\/th>How to use it<\/th><\/tr><\/thead>
Continuous torque<\/strong><\/td>Torque the motor can deliver without exceeding its stated temperature limit under specified cooling and ambient conditions.<\/td>Thermal path, ambient temperature, winding limit, drive current<\/td>Size the motor for steady operation and long duty cycles.<\/td><\/tr>
Peak torque<\/strong><\/td>Short-duration torque available within specified current, temperature, magnetic, and mechanical limits.<\/td>Peak current, saturation, demagnetization risk, shaft and drive limits<\/td>Check acceleration, shock load, and intermittent overload events.<\/td><\/tr>
\u0639\u0632\u0645 \u0627\u0644\u062a\u0648\u0642\u0641<\/strong><\/td>Torque at zero shaft speed under defined electrical and thermal conditions.<\/td>Rapid I\u00b2R heating, current limit, local hot spots<\/td>Use only with the stated test method and allowable duration; do not assume continuous operation.<\/td><\/tr>
Gearbox output torque<\/strong><\/td>Motor torque multiplied by ratio and gearbox efficiency.<\/td>Gear rating, efficiency, backlash, bearing and output-shaft capacity<\/td>Increase load-side torque when lower output speed is acceptable.<\/td><\/tr><\/tbody><\/table><\/div>

Seven Safe Ways to Increase Usable BLDC Torque<\/h2>

1. Verify the controller\u2019s current limits<\/h3>

Confirm the controller\u2019s continuous phase-current limit, peak phase-current limit, peak duration, switching frequency, and cooling condition. Also confirm whether its displayed current is DC-bus, phase peak, or phase RMS current. A mismatch here can make a correctly sized motor appear weak or can unintentionally overheat it.<\/p>

2. Improve commutation and rotor-position accuracy<\/h3>

Incorrect Hall-sensor order, encoder offset, phase order, or commutation timing reduces torque per ampere and can create extra heat. For servo applications, correctly tuned field-oriented control can align the torque-producing current with rotor flux and provide smoother low-speed torque. Always follow the drive manufacturer\u2019s identification and tuning procedure.<\/p>

3. Improve heat transfer for higher continuous torque<\/h3>

Use the mounting surface, housing, thermal interface, airflow, or liquid cooling specified for the motor. Monitor winding temperature when possible; housing temperature can lag behind internal hot spots. Better cooling may raise continuous current capability, but it does not authorize exceeding peak current, magnet temperature, insulation, bearing, or shaft limits.<\/p>

4. Provide adequate voltage headroom at the required speed<\/h3>

If torque falls at higher speed even though temperature is acceptable, the drive may be voltage-limited by back EMF. Select a compatible bus voltage, winding, and controller so commanded current remains achievable at the required speed. Respect maximum motor speed, controller voltage, regenerative voltage, and insulation limits.<\/p>

5. Add suitable gear reduction<\/h3>

A gearbox can multiply torque at the load while reducing output speed. Estimate output torque as motor torque \u00d7 ratio \u00d7 gearbox efficiency, then verify the gearbox\u2019s continuous, peak, radial-load, axial-load, and life ratings. Include backlash and reflected inertia when positioning performance matters.<\/p>

6. Select a more suitable motor or winding<\/h3>

When the present motor is already at its electrical or thermal limit, choose a BLDC motor with more active copper and magnetic volume, a higher continuous torque rating, or a winding matched to the available voltage and speed. Faradyi\u2019s brushless DC motor range<\/a> can be used as a starting point for comparing form factors and application options; final selection should be confirmed against a model-specific datasheet and operating point.<\/p>

7. Reduce avoidable drivetrain losses<\/h3>

Check bearing preload, seal drag, shaft alignment, coupling misalignment, brake release, belt tension, gearbox condition, and load mechanism friction. Removing parasitic torque does not increase electromagnetic motor torque, but it increases the torque available to the load and can reduce current and heat.<\/p>

Why \u201cJust Increase the Voltage\u201d Can Be Misleading<\/h2>

With a simple voltage-driven motor, higher applied voltage at zero speed can force more current through the winding resistance and produce more torque\u2014but it can also exceed current and temperature limits almost immediately. In a properly current-regulated BLDC servo system, the current command and limits determine low-speed torque. Raising the bus voltage above what is needed for current regulation does not automatically raise torque.<\/p>

Voltage becomes especially relevant as speed and back EMF increase. The correct design question is: Does the controller have enough voltage headroom to maintain the required phase current at the target speed?<\/em> That is more useful\u2014and safer\u2014than treating voltage as a universal torque adjustment.<\/p>

Troubleshooting Low Brushless DC Motor Torque<\/h2>
  1. Measure speed, phase current, bus voltage, and temperature together.<\/strong> A torque complaint cannot be diagnosed from voltage alone.<\/li>
  2. Compare the operating point with the motor curve.<\/strong> Check continuous torque, peak torque, rated speed, duty cycle, and cooling conditions.<\/li>
  3. Confirm controller conventions.<\/strong> Verify phase current versus bus current and RMS versus peak values.<\/li>
  4. Check commutation.<\/strong> Validate phase order, Hall states, encoder direction, electrical angle, and FOC identification.<\/li>
  5. Inspect the mechanical load.<\/strong> Look for binding, misalignment, excess preload, gearbox damage, or an unreleased brake.<\/li>
  6. Review thermal behavior over time.<\/strong> Torque that starts strong and then falls may indicate thermal limiting, rising winding resistance, or controller derating.<\/li>
  7. Use controlled test equipment.<\/strong> Verify torque on a guarded dynamometer or calibrated torque transducer rather than relying on an uncontrolled locked-shaft test.<\/li><\/ol>

    How to Select a BLDC Motor for a High-Torque Application<\/h2>

    Start from the load profile, not a single stall-torque number. Define the required load torque and speed for each part of the motion cycle, calculate RMS torque for thermal sizing, and separately verify peak torque and acceleration. Then check motor speed, drive current, voltage headroom, thermal path, inertia, mechanical interface, feedback, and environmental requirements.<\/p>

    For a useful engineering quotation, provide:<\/strong><\/p>