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HOW INNOVATIVE ROTOR DESIGNS CAN ENHANCE MOTOR PERFORMANCE
Brushless direct current (BLDC) motors are often specified to maximise efficiency and torque density, and open rotor designs can further extend these capabilities. Heat build-up can limit performance, but specific designs can be achieved to aid heat dissipation. Developments achieved by Portescap’s R&D team help to drive forward new technology across all miniature motor applications. Compared to their brushed design
counterparts, brushless motors can achieve higher efficiency, as well as greater torque and power density, and this is particularly true of outer rotor BLDC motor designs. In this configuration, the rotor and magnet assembly spins around the outside of the stator and its windings, which form the centre of the motor. The outer rotor setup can achieve higher
torque, and can also optimise efficiency. This is largely thanks to the increased rotor surface area, combined with its external position, which enable it to dissipate heat more easily. While energy losses through factors such
as vibration should also be considered in BLDC design and specification, heat losses are the most significant challenge.
HEAT BUILD-UP Mechanical losses contribute to heat accumulation, but the most significant factor is copper losses, resulting from the resistance of the stator’s copper windings. The other major contributor to heat comes from the motor’s iron core losses, caused by harmonic flux or alternating magnetic fields, including hysteresis and eddy current losses. To combat the effects of heat build-up,
external rotor design techniques that increase heat dissipation can be considered. This was a project the Portescap R&D team worked on and was typical of the development of new motor designs. To test and identify the optimum approach,
the team compared a traditional, closed external rotor design, alongside an open slot rotor that would introduce additional air ventilation. A third design was also considered and included an integrated fan combined with an open slot rotor, which could potentially improve ventilation.
TESTING ROTOR DESIGNS While the stator’s copper losses are the main contributor to motor heat, all other types of losses contribute to the thermal resistance of the motor. This is mathematically determined by motor construction and speed variables. If speed is constant and the load increases, the iron and mechanical losses will tend to be constant with the temperature rise, primarily due to copper losses only. With equivalent thermal resistance, the maximum torque can be calculated at any speed based on data at a specific load point.
34 DESIGN SOLUTIONS MARCH 2025
After recording the temperature and equivalent resistance at various data points, an accurate power graph, including speed compared to torque, could be created. To compare
the performance characteristics of
the closed rotor, open slot rotor and integrated fan open rotor designs, the research team applied torque
to the motor with a dynamometer. The temperature rise of the coil was monitored until each motor reached its steady state, thermally stable temperature.
TORQUE INCREASE Tests of the three motor designs were carried out at speeds ranging from 0 to 8,000 rpm, at increments of 2,000 rpm. Power loss and thermal resistance of each motor were then calculated based on the measured resistance, current and stable coil temperature. The study showed that the thermal
resistance of both the open slot rotor and the integrated fan rotor decreased rapidly with an increase in speed. Instead, while the thermal resistance of the closed rotor decreased slightly at first, at speeds up to 3,000 rpm, thermal resistance then increased drastically from 5,000 rpm onwards. The result this thermal resistance impact had on torque generation was significant. Replacing the closed rotor with the open slot design increased the maximum torque from 54 mNm to 80.5 mNm at 8000 rpm, which represented a 47% increase in torque capacity. The test showed that the integrated fan rotor design pushed the maximum torque capacity further still, achieving 113 mNm at 8,000 rpm, a further 40% increase compared to the open rotor alone. Looking at power, plotting the maximum
torque versus speed also showed that the open rotor design could increase total power, while the integrated fan design significantly extended the total generation of watts.
R&D ACHIEVES OPTIMUM DESIGN Test situations like this show that specific designs can be analysed in bespoke projects, delivering the optimum outcome for the given conditions and work points. Moreover, the findings from these kinds of projects permeate across all motor technology development at Portescap, to the benefit of all customers. This is the advantage of working with a trusted miniature motion expert with decades of experience in customised motion control solutions.
Portescap
www.portescap.com
AN INTELLIGENT DRIVE FOR SINGLE-AXIS CONTROL OF BRUSHLESS DC MOTORS
Available from Mclennan, Portescap’s new PCR 56/06 EC SD is an intelligent drive for single-axis control of brushless DC motors. This is offered as an integrated hardware and software developer kit package for rapid product development- to-production timescales. Tailored for use with Portescap’s BLDC series miniature motors, the motion controller features a 350W drive stage in a compact package and includes Windows-based motion and diagnostic software with auto-tuning as well as C-based command sets. The PCR 56/06 EC SD includes S-curve, trapezoidal, velocity contouring and electronic gearing profiles with position, velocity and torque control modes. Powered from 12 to 56V DC with a continuous output of up to 5.5A, the drive stage features an advanced PID filter with velocity and acceleration feedforward providing smooth precision motion. Hall sensor and encoder feedback options are available. A module-only option without power supply is
offered for direct mounting on the customer’s PCB. With a footprint of less than 38mm x 38mm and a depth of just 16.8mm, this option facilitates a smooth transition from product development to cost efficient production. Control flexibility is further offered through a choice of Ethernet, Serial or SPI host communications. The new PCR 56/06 EC SD is suitable for medical
and life science equipment, small-scale robotic systems, and many other assembly and process automation fields, the company explains.
Mclennan T: 01252 531444
www.mclennan.co.uk MOTORS FOR HEAVY
DUTY APPLICATIONS Advanced Electric Machines (AEM) has unveiled HDRM300C, the second generation of its popular motor solution for heavy duty and commercial vehicle applications. Building on the success of its HDRM150 motor, this is
said to represent a major advancement in electric motor design, achieving conductor slot fill rates exceeding 80%. The HDRM300’s increased speed capability provides
greater flexibility for system integration across diverse applications. New plug-in connectors have replaced traditional gland fittings, simplifying the installation and maintenance process; and internal components, including upgraded bearings and robust busbar connections, have been strengthened to support the motor’s higher operational speeds. In addition, an improved motor cooling system allows the machine to work harder for longer.
Advanced Electric Machines
https://advancedelectricmachines.com/
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