Frameless PM Motor Sizing: Inputs to Confirm Before a Quote

This guide helps an OEM prepare a frameless motor inquiry. It does not list PMDD Motor catalog ratings or claim that a particular motor is available.

Start with the driven load

Record the continuous and peak torque the axis needs, the speed at each load point, and how long each point lasts. Include acceleration, deceleration, dwell, reversals, and the expected operating hours.

If you know shaft power and speed, the corresponding torque is:

This is a conversion between mechanical power and torque at a stated speed. It does not select a motor. Starting torque, peak duration, load inertia, losses, and the drive current limit still need review.

Describe the mechanical envelope

Provide a drawing or dimensions for the stator outside diameter, rotor bore, active stack, total axial height, mounting features, cable exit, and nearby hardware. Call out clearances that matter during assembly and operation.

For a frameless motor, the motor is integrated into the customer’s assembly. Bearing support, rotor retention, air-gap alignment, housing stiffness, and installation sequence therefore belong in the interface review. A nominal diameter alone does not establish interchangeability.

Define the thermal boundary

State the housing or heatsink material and dimensions, contact area, cooling method, ambient temperature, and any nearby heat sources. Also specify the temperature limits for the winding, magnets, adhesive, potting, sensors, and surrounding machine where known.

Continuous torque depends on the complete thermal path and the duty cycle. A value measured or calculated for one fixture should not be transferred to another housing without checking the boundary conditions. Ask the supplier to identify the mounting and test conditions behind any continuous rating it provides.

Match winding and drive requirements

Share the available DC bus or AC supply, continuous and peak current limits, maximum speed, feedback device, control mode, and cable length. Ask for winding resistance, inductance, back-EMF, and torque-constant data only with the measurement method, temperature, and current convention stated.

Do not assume that a motor will work with a named servo drive because the voltage or connector appears similar. The motor data, encoder interface, drive limits, and commissioning procedure need to be checked together.

Compare stator constructions on the application

Segmented and solid stators differ in assembly, winding access, structure, and how the motor transfers heat into the housing. There is no universal winner. Ask the supplier to explain the construction offered for the requested geometry and to provide the drawing and evidence that apply to that build.

RFQ checklist

• Load profile with continuous and peak torque, speed, duration, and duty cycle.
• Stator and rotor envelope drawing, axial clearance, mounting, and cable routing.
• Housing or heatsink details and operating environment.
• Supply, drive, feedback, and control requirements.
• Sample quantity, expected annual volume, destination, and required documents.
• Acceptance tests and limits required before shipment.

Treat every model, rating, drawing, certificate, test record, and delivery date as project-specific until it appears in a supplier-backed quotation.