Example Data Table
| Case |
Voltage |
Speed |
Torque |
Line Current |
Main Design Goal |
| Drone motor |
22.2 V |
7200 RPM |
0.45 N·m |
18 A |
High speed and low mass |
| E-bike hub |
48 V |
420 RPM |
32 N·m |
35 A |
Low speed torque |
| Industrial servo |
72 V |
3000 RPM |
4.5 N·m |
28 A |
Efficiency and thermal control |
Formula Used
Angular speed: ω = RPM × 2π ÷ 60
Mechanical output power: Pout = Torque × ω
Speed constant: Kv = No-load RPM ÷ Supply voltage
Back EMF constant: Ke = 60 ÷ 2πKv
Torque constant: Kt ≈ Ke in SI units
Copper loss: Pcopper = Phase count × Phase current² × Phase resistance
Electrical frequency: fe = RPM × Pole count ÷ 120
Efficiency: η = Output power ÷ Required input power × 100
Thermal rise: ΔT = Total loss × Thermal resistance
Current density: J = Phase current ÷ conductor area per path
How to Use This Calculator
Enter the supply voltage, no-load speed, rated speed, torque, and current first.
Add winding resistance, connection type, pole count, slot count, turns, and wire data.
Enter geometry values, including stack length, air gap radius, and flux density.
Add loss, controller, and thermal assumptions for a deeper design check.
Press Calculate to see results above the form.
Use the CSV or PDF buttons to save the current result set.
Brushless DC Motor Design Guide
A brushless DC motor links electrical input to magnetic force. Good design starts with a target torque, target speed, and supply voltage. These values set the basic power level. They also guide current, winding, and cooling choices.
Core Design Checks
The no-load speed gives a useful speed constant. A higher speed constant means more speed per volt. It often means less torque per ampere. The torque constant estimates how much current is needed for the shaft load. This relation helps size the driver and copper path.
Copper loss is a major heat source. It depends on phase current and winding resistance. Small resistance looks helpful, but it can need thicker wire and larger slots. Current density shows how hard the conductor is working. High values may be acceptable for short bursts. Continuous duty needs a lower value.
Magnetic and Mechanical Factors
Pole count affects electrical frequency. More poles can give smooth torque at low speed. They also raise switching frequency for the controller. Slot count affects winding layout, cogging, and manufacturability. The slots per pole per phase value gives a fast geometry check.
Air gap flux density helps estimate magnetic loading. Stack length and radius shape torque capacity. A longer stack raises active volume. A larger radius improves torque leverage. These changes also affect mass and cost.
Thermal Planning
Efficiency is not only a marketing number. It decides battery life and cooling demand. Copper, iron, mechanical, and controller losses all add heat. Thermal resistance converts those losses into a temperature rise. The estimated winding temperature should stay below the chosen limit.
Practical Use
This calculator is best for early sizing. It compares assumptions before detailed finite element work. Change one value at a time. Watch current density, copper loss, voltage margin, and temperature. If any warning appears, revise the winding, voltage, cooling, or load target. A final design still needs prototype testing. It should also meet insulation, vibration, bearing, and controller limits.
Design Review
Record every assumption with units. Keep a margin between rated speed and available voltage. Compare calculated bus current with driver limits. Check whether the selected wire can fit the slot. Revisit magnets, laminations, and cooling when targets change during early testing.
FAQs
What does Kv mean in this calculator?
Kv is the estimated no-load speed per volt. It helps compare winding choices. A high Kv motor spins faster for the same voltage, but usually gives less torque per ampere.
Is Kt always equal to Ke?
In SI units, Kt and Ke are closely related. Real values depend on waveform, connection, measurement method, and motor construction. Use the result as an early design estimate.
Why is copper loss important?
Copper loss becomes heat inside the winding. It rises with the square of phase current. Reducing resistance or current can greatly improve continuous performance.
What does voltage margin show?
Voltage margin compares supply voltage with estimated back EMF at rated speed. Low or negative margin means the motor may not reach the target speed under load.
Why enter pole count and slot count?
These values affect electrical frequency, winding layout, cogging behavior, and manufacturability. The slots per pole per phase value gives a quick geometry review.
Can this replace detailed motor simulation?
No. This tool supports early sizing and comparison. Final design should use electromagnetic simulation, thermal modeling, material checks, and prototype testing.
Which losses are included?
The calculator includes copper loss, iron loss, mechanical loss, and controller loss. You can edit assumptions to match your design stage or test data.
What should I do if temperature is too high?
Reduce current, increase wire area, improve cooling, lower winding resistance, use better laminations, or revise torque goals. Also check insulation class and duty cycle.