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V012024 • © 2024 Portescap. Specifications subject to change without notice.Glossary (for Brushless Slotless DC Motors)General DataMaximum motor speed This is the maximum recommended speed as limited by the bearing assembly type, taking into account the bearing supplier’s specification, vibration behavior and other factors.Ambient working temperature range The recommended ambient working temperature range is based on the properties of the bearing lubricant.Ambient storage temperature range The recommended ambient storage temperature range is based on the properties of the bearing lubricant.Ball bearings preloadThis is the bearing preload force as implemented by design. This might be a static preload in bearings bonded to the shaft after assembly. In that case, it is not possible to measure preload force by applying an external force on the shaft, and there is vey little axial play. To maximize bearing life, we recommend that forces on the shaft during operation do not exceed the preload force.Axial static force without shaft support (max)When press-fitting a part onto the shaft without providing support on the opposite end of the shaft, the applied force is supported entirely by the bearing races. This is the maximum pressing force recommended to avoid damage to the bearings.Maximum winding temperatureThis specification is linked to the properties of the thermo-bonding material around the coil copper wires. The maximum winding temperature can be an important consideration for applications that require long product life because operation at high temperatures can lead to failure modes such as fast aging of the bearing lubricant.Thermal resistanceThermal resistance is given either directly from the coil to the ambient air surrounding the motor, or in two steps: from coil to housing and then from housing to ambient.This value is calculated with the motor in the air at 25°C, with no heat sink or forced air cooling. With the motor installed, the value is likely to decrease in many applications, but it could also be higher if the motor is surrounded by a small volume of air that cannot cool down.Thermal resistance varies with air convection parameters, and is lower at a high temperature of the motor housing. The value can also vary based on speed, especially with flat motors.This value is measured during operation close to the maximum continuous power zone (see power curve graph).Thermal time constantThis value is given directly from the coil to the ambient air surrounding the motor. Along with the thermal resistance, the thermal time constant allows for solving thermal differential equations for the motor. It is measured at a constant voltage supply over time, which means the amount of power loss that can be dissipated tends to decrease due to the increase in winding resistance with increasing temperature.Mass This is the total motor mass, including cables.Rotor inertia This assumes an unconnected rotor and is used to determine angular acceleration for a given torque.Hall sensor electrical phasing In a three-phase BLDC motor with Hall sensors, the sensors are commonly phased at 120° electrically from each other. (See the chart to the right for an example.) This affects driver selection.14