Custom Brushless DC Motors: BLDC, DC and AC, Sorted Out
By the Turncircles engineering team · Published
"Custom DC motors", "custom brushless DC motor", "custom AC motors": three search terms, one confusing aisle. The motor world calls the same machine a BLDC to the person looking at the battery and a PMSM to the person looking at the winding, and both are correct.
This page sorts the vocabulary, says which motors we build and which we do not, and lists what a custom BLDC design is actually defined by.
Configure a brushless motor Read the custom electric motors guideThe Motor Family, Without the Jargon
| Type | How it commutates | Strengths | Do we build it? |
|---|---|---|---|
| Brushed DC | Carbon brushes on a commutator | Simple, cheap, runs from a battery directly | No |
| Brushless DC (BLDC) | Electronic drive switches the phases | Efficient, long life, no brush wear | Yes, axial flux |
| Permanent magnet synchronous (PMSM) | Electronic drive, sinusoidal currents | Smooth torque, high efficiency | Yes, same machine, different drive |
| Induction (AC) | Rotating field induces rotor currents | Robust, mains-driven, no magnets | No |
| Stepper | Drive steps the rotor position | Holds position without feedback | No, see BLDC actuators vs steppers |
Brushes are the motor equivalent of a smoker's cough: perfectly functional for a while, and then you hear them. Replacing them with an electronic drive is why brushless motors last longer and run more efficiently.
"Custom DC Motor" and "Custom AC Motor": Sorting the Search Terms
A custom brushless DC motor from us runs from a DC supply (up to 370 VDC) through a three-phase drive. Inside the motor the phase currents are alternating. So the same machine is a "DC motor" to the person who looks at the battery and an "AC motor" to the person who looks at the winding. Both are right, and both are searching for the same thing.
If your phrase was "custom AC motor" and what you need is a mains-driven induction motor on a fixed frequency, we are the wrong supplier and will tell you so. If what you need is a permanent magnet synchronous motor for a variable-frequency drive, welcome.
What a Custom BLDC Motor Is Defined By
These are the numbers your supplier needs, and the ones the configurator lets you set or read:
- Supply voltage and current limit, which decide the winding and how much copper the motor needs.
- Torque and speed at the operating point, continuous and peak, not only the maximum.
- Torque constant (Kt) and back-EMF constant (Ke). They are the same quantity in SI units, and they tie speed to voltage and torque to current.
- Phase resistance and inductance, which affect the controller and the current ripple.
- Pole count and winding layout, which affect smoothness and harmonics. See the winding calculator.
- Position sensing, sensorless or with sensors, which depends on your drive.
- Size, mounting, protection and temperature.
A Worked Example: Kt, Ke and Your Supply Voltage
Suppose a custom BLDC motor has Kt = Ke = 0.10 in SI units (Nm per ampere, volts per radian per second). To deliver 5 Nm it needs about 50 A. At 3,000 RPM (314 rad/s) its back-EMF is about 31 V. On a 48 V supply that leaves roughly 17 V of headroom for the winding resistance and the controller, which is comfortable at moderate currents and tight at the peak. Move the same motor to a 24 V supply and it cannot reach 3,000 RPM at all.
That is the quiet reason custom winding matters: the same magnets and the same copper can be wound for 24 V, 48 V or 370 V, with different Kt, and the right choice depends on your supply and speed, not on which datasheet had the nicer photo.
Illustrative numbers, not a specific Turncircles motor.
Why Axial Flux for Custom BLDC
A brushless motor can have any geometry, and radial flux is the common one. When weight, axial length or torque at low speed matter, the axial flux layout wins on torque per gram, which is why we build only that. A printed stator replaces the wound coil and the iron core, so the winding is a manufactured part that is repeatable and quick to change. For the comparison, see axial flux vs radial flux motors; for the broader context, the custom electric motors guide.
Controller Notes
A BLDC motor does nothing without a drive. Make sure the controller can supply the voltage and phase current of the motor, handle its inductance (a coreless stator has low inductance, which raises current ripple and calls for a higher switching frequency), and use the position feedback you have. If you tell us which drive you plan to use, we can design the winding to suit it.
Frequently Asked Questions
What is a custom brushless DC motor?
A brushless DC motor whose winding, magnets and dimensions are designed for a specific application instead of chosen from a catalogue. It uses permanent magnets and an electronic drive in place of brushes and a commutator.
Is a BLDC motor AC or DC?
It is supplied from DC, but the drive converts that into alternating phase currents for the winding. So at the terminals of the motor it is three-phase AC, and at the supply it is DC.
Do you build custom AC induction motors or brushed DC motors?
No. We build permanent magnet brushless motors in axial flux form. Brushed DC and induction motors are well served by catalogue manufacturers.
What information do I need to order a custom BLDC motor?
Supply voltage, torque and speed at the operating point (continuous and peak), the space available, the environment and your controller. The motor selector guide shows how to work them out.
What voltage can a custom BLDC motor run on?
Turncircles motors cover supplies up to 370 VDC. The winding is designed for your supply voltage and current limit.
Configure a custom brushless motor
Enter voltage, torque and speed. See the motor.
Configure your motor Talk to an engineer