The Geometry Data section in Motor Wiz is a critical part of motor design, as it defines the physical dimensions and spatial relationships of the motor’s components. From a user perspective, this section provides both a design canvas and a simulation tool, enabling engineers to explore how dimensional choices affect torque, efficiency, cooling, and material usage.
Geometry parameters interact closely with material selection, winding configuration, and thermal properties, meaning that any change in geometry must be validated against motor performance and thermal limits. Motor Wiz allows users to tweak these parameters and immediately observe their effects on torque density, losses, and thermal performance, fostering an iterative design workflow.
Key attributes include:
i. Aspect Ratio (Active Length / Rotor Outer Diameter)
The Aspect Ratio is a key design parameter in electric motors, defined as the ratio of the active length (axial length) to the rotor outer diameter. It plays a significant role in motor performance, efficiency, and cooling.
A higher aspect ratio (≥1.5) results in a longer and narrower motor, which tends to have higher torque density and efficiency but may require better cooling mechanisms due to increased winding resistance.
A lower aspect ratio (≤1.0) creates a shorter and wider motor, making it more compact and easier to cool but possibly reducing torque density due to limited active length.
The selection of aspect ratio depends on the motor application—higher values are preferred in high-efficiency and high-power applications, while lower values suit compact designs with better cooling.
ii. Air Gap
The Air Gap is the smallest physical clearance between the rotor and stator, crucial for magnetic flux generation and motor efficiency.
Small air gaps (<0.5 mm) improve magnetic coupling and torque output but increase manufacturing precision requirements and the risk of rotor-stator contact.
Larger air gaps (>2 mm) reduce magnetic saturation issues but weaken magnetic field strength, lowering torque and efficiency.
Optimal air gap selection ensures minimal losses while maintaining mechanical safety margins.
iii. Tooth Height Factor
The Tooth Height Factor defines how the stator's magnetic flux path is distributed in relation to winding space.
Higher values (≥0.6) indicate taller teeth, improving flux conduction but limiting slot area for windings, which may reduce current-carrying capacity.
Lower values (≤0.3) mean deeper slots, allowing for more copper windings and better current handling but potentially increasing core losses.
An optimized tooth height factor balances flux efficiency and winding capacity for improved performance.
iv. Torque per Rotor Volume (TRV Max)
Torque per Rotor Volume (Trv Max) is a performance density metric that evaluates how efficiently the motor can generate torque relative to its physical size. It is a critical factor in power-dense applications like EVs, aerospace, and robotics.
High Trv Max (>20 Nm/cm³) means the motor is compact yet powerful, often achieved through high-energy magnets, advanced cooling, and optimized winding designs.
Low Trv Max (<5 Nm/cm³) indicates a larger and bulkier motor with lower torque density, common in applications where size is not a constraint, like industrial pumps and fans.
Balancing Trv Max is essential to minimize size without compromising efficiency and thermal stability.
v. Pole Pairs
Pole Pairs (P) represent the number of north-south magnetic pole pairs in the motor, influencing speed, frequency, and efficiency.
Few pole pairs (1-4) allow for high-speed operation, ideal for aerospace and automotive traction motors.
Many pole pairs (10-50) improve low-speed torque and efficiency, suitable for direct-drive applications like wind turbines and large industrial motors.
vi. Slot Number
Slots house the stator windings, influencing electromagnetic performance and losses.
Fewer slots (≤12) reduce iron losses but may increase torque ripple.
More slots (lesser than 48) smooth flux distribution and reduce harmonics, improving efficiency at the cost of higher manufacturing complexity.
Slot-pole combinations must be carefully chosen to minimize cogging torque and optimize motor performance.
vii. Turns per Coil
The number of times a conductor (usually copper wire) is wound around a stator tooth or coil form in an electric motor.
Why It Matters
More turns → Higher induced voltage (back EMF)
Fewer turns → Higher current capacity, lower resistance
Impacts
Affects torque, speed, efficiency, and thermal performance
Needs to be balanced with wire gauge and slot space
Design Tip
Use turns per coil to match motor characteristics (voltage, current, torque) to the application.