Learn electric motor design
Practical guides on the fundamentals — written for engineers who want to understand the physics behind the calculations.
Windings 7 articles
Winding factor, harmonics and slot/pole choices.
Fundamentals
- What is winding factor and why does it matter in motor design?Understand how the distribution factor and pitch factor combine to determine how efficiently a winding converts current into torque-producing flux.
- Coil pitch factor — how a winding captures rotor fluxHow slot electrical angles, coil span, and induced voltage combine into kp = sin(β/2). Includes a worked numerical example for a 12-slot / 4-pole machine with three valid coil pitches.
- Winding distribution factor — why spreading conductors costs EMFHow distributing a phase across multiple slots staggers EMF phasors and gives kd = sin(q·α/2) / (q·sin(α/2)). Includes a worked numerical example for 12, 24, and 36-slot machines.
- How to calculate the winding factor of a given winding distributionThe vector-summation method, from slot angles to the resultant phasor. Two fully worked examples: a 12-slot / 8-pole two-layer tooth-coil winding (kw1 = 0.866) and a 48-slot / 8-pole single-layer concentric winding (kw1 = 0.966).
Slot/pole choices
- MMF harmonics in three-phase AC windingsLearn how the spatial distribution of conductors creates a magnetomotive force spectrum — and why higher harmonics cause torque ripple and additional losses.
- Integer-slot vs fractional-slot windings — when to use eachThe slots-per-pole-per-phase ratio q determines fundamental winding behaviour. Learn the trade-offs between distributed and tooth-coil winding configurations.
- 12s/14p vs 12s/10p: a mirror-image winding pair explainedBoth configurations share an identical winding factor of 0.933, yet differ significantly in cogging torque, operating frequency, and MMF harmonic structure. A side-by-side breakdown for drone and EV motor designers.
Electrical steel & core loss 4 articles
Reading steel data, where iron loss comes from, and how to model it.
- How to read an electrical steel B-H curveDecode the magnetisation curve: what saturation, permeability, and the hysteresis loop tell you about a steel grade's suitability for your motor core.
- Why electrical steel has core loss: hysteresis, eddy current and excess lossHow the B-H loop sets hysteresis loss, how permeability and sheet thickness set eddy-current loss, and a loss split worked on real M270-35A and M270-50A datasheet data.
- How core loss is measured: the Epstein frame, single-sheet tester and IEC 60404 standardsWhat the W/kg on a datasheet actually means: the Epstein test step by step, the standards behind grade names like M270-35A and 35C270, and what the test leaves out.
- Core loss models compared: Steinmetz, Bertotti and beyond — when to use eachWhy loss equations have exponents like 1.6, 2 and 1.5, what the Steinmetz exponents really measure, and how five models compare on real M270-35A data, inside and outside the fitted range.
Permanent magnets 1 article
Choosing magnet grades.
Torque & performance 1 article
Torque quality and slot-pole trade-offs.
Motor constants & control 2 articles
Datasheet constants and FOC set-up.
- Kv, Kt and Ke: one motor constant in three unitsWhy the speed, torque and back-EMF constants are one number, how to convert them for brushed DC and BLDC motors, and where the factors of √3, √2 and 1.5 come from. Worked through on the maxon RE 40 and ODrive D5065 datasheets.
- Winding sequence, rotation direction and rotor angle for FOCHow the phase winding order sets the direction of the rotating field, which way the rotor angle must count, what swapped phases look like under FOC, and how to identify the right terminal order and encoder offset on the bench.