BRUSHLESS OUTRUNNER DESIGN
From shaft torque to motor.
Compare geometry, windings, current, and copper heating.
01 / ELECTROMAGNETIC GEOMETRY
Pancake outrunner
02 / OPERATING POINT
Current, heat & speed
03 / GEOMETRY SENSITIVITY
Diameter versus required loading
Fixed target torque and stack length. Larger diameter reduces the shear stress required; it does not establish what the magnetic design can produce.
04 / CURRENT SENSITIVITY
Kᵥ versus required current
Fixed target torque, using the paper’s peak q-axis current convention. The dashed line is your entered current limit.
Compare speed constants Same-geometry rewind
Hypothetical windings from the reference inputs. Maximum phase resistance is the hot resistance allowed by your copper-loss budget.
Winding construction Turns, wire & resistance
Fixed geometry, connection, copper fill, mean turn length, and temperature. This comparison is separate from the entered operating-point resistance.
Lower Kᵥ increases torque per ampere. Ideal rewinding reduces current but raises resistance, leaving copper loss unchanged at the same torque.
Geometry candidates from the paper Compare dimensions
All rows use your current target torque. Air-gap diameter is approximated by stator diameter for the paper comparison rows.
Reduction, speed & reflected inertia Transmission checks
Follow the equations Paper §3.7 & Appendix A
Other design factors Magnetic, winding & mechanical design
Magnetic circuit
Magnet grade and thickness, air gap, magnet coverage, stator teeth, steel grade, lamination thickness, and back-iron dimensions affect flux, saturation, and losses. These need magnetic analysis and measurements; diameter and Kᵥ alone cannot determine them.
The rotor’s ferromagnetic return ring carries flux. Machining controls alignment and air-gap geometry; aluminum and ordinary printed polymer do not replace magnetic steel.
Winding construction
Turns, wire cross-section, parallel strands, slot fill, winding layout, and end-turn length set the actual resistance and winding factor. Exact wire sizes need slot dimensions and an insulation allowance.
The electrical model uses balanced star-connected phases. Delta windings and other current conventions must be converted before using these equations. Slots and poles describe a candidate layout, not a verified winding design or cogging prediction.
Cooling & control
Cooling, winding temperature, duty cycle, saturation, rotor balance, magnet retention, bearings, FOC bandwidth, and inverter limits determine usable performance. Copper budgets exclude core, bearing, drive, cable, and transmission losses.
Holding torque creates heat with zero mechanical output. Low reduction and forward efficiency alone do not prove backdrivability; measure breakaway torque and hysteresis.
Editable design assumptions. Detailed input and output definitions are in the paper’s ActuationLab Calculator Reference.