Why Are Coreless Motors Popular in Medical Devices?

Coreless motors are popular in medical devices because their ironless or slotless design eliminates iron-core cogging torque, a primary source of low-speed torque ripple and vibration. This construction supports the smooth, quiet, and responsive motion required for precise, patient-friendly equipment such as handheld instruments, diagnostic systems, and drug delivery pumps.

These advantages are especially valuable where small motion irregularities can affect measurement accuracy, fluid delivery, image stability, or operator control. However, the final result still depends on the complete motion system, including the motor type, driver, feedback method, mounting structure, and thermal environment.

Modern medical devices are becoming smaller, more portable, and more precise. Whether used in a surgical tool, a laboratory analyzer, or an infusion pump, the motor must deliver reliable motion without compromising performance, patient comfort, or operator control¹. For OEM medical device engineers, the question is not just whether the motor can provide enough speed or torque, but whether it can deliver stable, controlled motion inside a sensitive medical environment. This is where coreless motor technologies offer clear system-level advantages.

What Makes Coreless Motors Different From Iron-Core Motors?

The key difference lies in the motor’s construction, which directly influences its performance characteristics. While a conventional DC motor uses copper windings wrapped around a heavy, laminated iron core, coreless motor designs are engineered to reduce mass, inertia, and cogging-related disturbances.

In the context of medical devices, the term "coreless motor" often refers to two distinct technologies. Brushed coreless motors remove the laminated iron core from the rotating armature, while brushless slotless motors eliminate the toothed stator structure around the air gap. Their construction differs, but both can reduce cogging-related disturbances and support smooth motion when properly designed and controlled.

• Brushed Coreless DC Motors: These feature a unique self-supporting, basket-like rotor made of copper windings, which rotates around a stationary internal magnet. With no iron in the rotor, its inertia is very low. Commutation is mechanical, using brushes and a commutator. They are often chosen for applications requiring fast dynamic response and a simple drive architecture.

• Brushless Slotless Motors: These motors use a permanent-magnet rotor and a stationary, toothless winding arrangement. The absence of stator teeth eliminates iron-core cogging.² Commutation is electronic, requiring a compatible driver and often Hall sensors or an encoder. They are frequently considered for applications requiring long life, high speed, and continuous duty.

The elimination of an iron-core rotor or toothed stator provides several key advantages over traditional slotted iron-core motors:

• No Iron-Core Cogging Torque: A primary source of low-speed torque ripple is eliminated, resulting in smoother motion.
• Low Rotor Inertia (Brushed Coreless): Reduces the torque required to accelerate the motor’s own rotating mass, supporting rapid speed changes when external load inertia is properly controlled.
• Lower Motor-Generated Vibration: Smoother magnetic flux interaction reduces a key source of magnetic excitation.
• Favorable Power-to-Weight Ratio³: Supports the design of compact and ergonomic devices.

Why Medical Devices Require Smooth, Low-Noise Motion

In a medical setting, noise and vibration are not just comfort issues; they can directly impact patient comfort, operator focus, and the perceived quality of the equipment. A noisy or vibrating device can cause patient anxiety, interfere with diagnostics, and be seen as poorly made.

These issues are a system-level problem. A motor’s vibration, even if small, can be amplified by the device’s housing and structure, turning a minor buzz into an irritating whine.

From our experience, finished-device noise is often affected more by mounting and housing resonance than by the motor alone⁴. Motor-generated noise and vibration can originate from:

• Electromagnetic Sources: Torque ripple from commutation (brush or electronic) and PWM current.
• Mechanical Sources: Bearing friction, rotor imbalance, and gear train meshing.
• Structural Resonance: When the motor's operating frequency excites a natural frequency of the device's structure.

Coreless and slotless designs address this problem at the source. By eliminating iron-core cogging, they remove one important source of low-speed magnetic vibration. This improves the motor’s baseline motion quality, but it does not eliminate all sources of torque ripple or system vibration. The final noise performance must be evaluated at the complete-device level. This is especially important for:

• Portable diagnostic devices used at a patient's bedside
• Handheld analytical tools used in quiet laboratories
• Infusion pumps and other drug delivery systems

How Low Inertia Improves Dynamic Response and Control

Many medical devices do not just spin at a constant speed; they need to execute rapid and predictable speed changes. This capability, known as high dynamic response, is critical for both automated processes and user-controlled tools.

A motor’s ability to change its speed rapidly is related to inertia. The lightweight, self-supporting rotor of a brushed coreless motor has very low inertia, requiring less torque to accelerate its own rotating mass.

The fundamental equation of motion is: Net Torque = Total Inertia × Angular Acceleration

Here, Total Inertia includes both the motor’s rotor inertia and the inertia of the external load (gears, tools, etc.) reflected back to the motor shaft. Low rotor inertia provides the greatest benefit when it represents a meaningful part of the total system inertia. This allows for faster acceleration under the same torque and load conditions.⁵

This responsive behavior is important in applications like:

• Surgical Drills and Saws: Where the surgeon expects immediate tool response to trigger input.
• Pipetting Robots: Which must move quickly and stop precisely to handle micro-liter volumes accurately.
• Haptic Feedback Systems: Where the actuator must produce rapid, repeatable changes in torque or direction according to the required feedback profile.

System-Level Observation: A high-response motor cannot compensate for a slow or poorly tuned control system.⁶ The motor may be capable of rapid acceleration, but if the driver's current capability is limited or the control loop is slow, the overall system performance will be sluggish. The motor, driver, and controller must be designed and tuned as an integrated motion system.

How Coreless Motors Support Compact Medical Devices Within Thermal Limits

The industry trend toward portability is clear, requiring smaller, lighter, and more power-efficient components. Compact size is valuable only when the required torque and speed can be maintained within acceptable winding and housing temperatures.

Coreless motor technologies can help meet output requirements within a smaller package, provided that thermal and duty-cycle limits are properly evaluated. Their low moving mass and compact winding structures can provide a favorable power-to-weight ratio. However, continuous torque capability still depends heavily on winding temperature, heat transfer, and duty cycle.

Datasheet continuous ratings are valid only under the manufacturer’s stated ambient temperature, mounting, and heat-dissipation conditions.⁷ Inside a sealed enclosure with limited thermal conduction, substantial derating may be required.

When evaluating compact motors, our engineering team typically asks:

• What is the actual duty cycle—for example, 2 seconds on followed by 10 seconds off?
• What is the peak torque required, and for how long?
• What is the maximum ambient temperature expected inside the sealed device housing?
• Is the motor mounted to a metal frame or other structure that can act as a heat sink?

Continuous performance should be confirmed through thermal modeling and prototype testing under representative and worst-case operating conditions.

How Brushed and Brushless Coreless Motors Fit Different Medical Requirements

The choice between a brushed coreless motor and a brushless slotless motor is a critical OEM decision based on application-specific trade-offs. Neither is universally better; they solve different problems.

A brushed coreless motor offers a simple drive architecture and excellent dynamic response due to its low rotor inertia, while a brushless slotless motor provides longer service-life potential and is often considered for high-speed or extended-duty applications.

For a disposable or limited-life tool requiring fast response, a brushed coreless motor may be a good fit. For applications requiring long operating life or extended continuous duty—such as respiratory blowers or continuously operating analytical modules—a brushless slotless design is often considered.

What OEM Engineers Should Confirm Before Motor Selection

Selecting a motor for a medical device requires a more rigorous process than for general industrial products. OEM engineers must consider performance, reliability, safety, and environmental factors at the system level.

Providing a comprehensive specification is the most important first step to getting a well-matched motion solution. This checklist covers key areas to define with your motor supplier.

Performance & Control:

• Operating Voltage and Current Limits
• Speed, Torque (Continuous & Peak), and Duty Cycle
• Load Inertia and Friction
• Control Method: Open-loop vs. closed-loop (speed, position, or torque)
• Feedback Requirements: Encoder resolution or Hall sensors
• Driver/Controller Specs: PWM frequency, control loop bandwidth

Reliability & Environment:

• Lifetime Target: Defined in operating hours or number of cycles.
• Sterilization/Cleaning Exposure: Standard motors should not be assumed to withstand autoclave sterilization unless specifically designed and validated. Confirm the exact method (e.g., Autoclave, ETO, Gamma), temperature, pressure, number of cycles, and chemical exposure.
• Thermal Conditions: Ambient temperature range inside the device and available heat sinking.
• Noise & Vibration Limits: Define measurable targets under specified operating conditions. For example, a project may require less than 45 dBA at 1 meter at a defined speed and load. Vibration limits should also specify the measurement axis and frequency range.
• EMI/EMC Requirements: The complete device must be validated. Motor-level considerations include shielding, filtering, and grounding.

Safety & Mechanical Integration:

• Failure Modes: Define safe behavior during stall or overload. Is current limiting or thermal protection required? Is particle generation from brush wear a concern?
• Biocompatibility: Biological safety requirements (e.g., per ISO 10993) should be evaluated at the device level based on whether motor materials have direct or indirect patient contact.
• Mechanical Interface: Dimensions, mounting, shaft features, and connector/cable requirements.

Application Guide: Where Coreless Motors Are—and Are Not—a Strong Fit

Coreless motor technologies are a strong choice for medical applications where motion quality is a priority, but they are not a universal solution. Understanding their strengths and limitations helps in making the right selection.

They excel where traditional motors may fall short in smoothness, responsiveness, and power-to-weight ratio. However, for applications prioritizing very high continuous torque or lowest possible cost, a different motor architecture might be more appropriate.

Coreless or slotless motors may be less suitable when an application requires:

• Extremely high continuous torque density (where a slotted brushless motor with better thermal dissipation may be preferred).
• The lowest possible system cost for a simple, constant-speed task where noise and vibration are not primary concerns.

Conclusion

Coreless motor technologies are widely used in medical devices because they support smooth, quiet, and responsive motion in compact systems. However, the right choice depends on more than the coreless structure itself. OEM engineers must evaluate whether a brushed or brushless solution best matches the required performance, lifetime, control strategy, thermal conditions, and cleaning or sterilization exposure.

For a medical device motor evaluation, provide the target voltage, speed, continuous and peak torque, duty cycle, lifetime, control method, environmental exposure, and mechanical interface. BODENMOTION can help compare suitable brushed and brushless coreless motor options and identify the parameters that should be verified during prototype testing. Contact our engineering team at info@bodenmotion.com.

FAQ

Q1: Why are coreless motors used in medical devices?

Coreless motors are used because their ironless or slotless design eliminates iron-core cogging torque, supporting the smooth motion, low vibration, and fast response needed for precise, quiet, and user-friendly medical equipment.

Q2: What is the difference between brushed and brushless coreless motors?

A brushed coreless motor has a lightweight, ironless rotor and uses mechanical brushes for commutation, offering simple control. A brushless slotless motor uses a permanent-magnet rotor, a toothless stator winding, and electronic commutation, offering longer service-life potential for high-speed or extended-duty applications.

Q3: Can a coreless motor withstand autoclave sterilization?

Only if it has been specifically designed and validated for it. Standard motors should not be assumed to survive autoclaving. Materials for the magnets, windings, adhesives, bearings, and sensors must be chosen to withstand repeated high-temperature, high-pressure steam cycles.

Q4: How should motor noise and vibration be specified?

Noise and vibration should be specified as a measurable limit under defined operating conditions. For example, a noise target could be below 45 dBA at 1 meter at a certain speed and load. These parameters should be tested and validated in the final device assembly.

Q5: What information should an OEM provide before requesting a motor recommendation?

Provide a complete system specification: performance needs (voltage, speed, torque, duty cycle), control method, mechanical interface, lifetime target (in hours or cycles), and all environmental conditions, including temperature, cleaning, and sterilization exposure.