My open source PCB motor is a smaller, cheaper and easier to assemble micro brushless motor.
What unique about this motor design is that the stator is printed on a 4-layer PCB board. The six stator poles are spiral traces wounded in a star configuration. Although these coils produce less torque compared to an iron core stator, the motor is still suitable for high-speed applications.
The current prototype has a 3d printed rotor with a 16mm diameter.
My PCB-Motor is made from a 6-pole stator printed on a 4-layer PCB and a 4-pole 3d printed rotor. Its has an outer diameter of 16mm and is rated at 1 watt.
I had this idea when I was trying to design a small compact drone. The PCB motor is much cheaper than other micro brushless motors and also easier to assemble. My goal is to make the rotor part of the BOM and mounted just like any other component on a PCB.
So torque is the biggest weakness of my tiny PCB motor. This was measured it to be 0.9gcm.
But it is something that can be improved. These are three ways how I tried to improve it:
Double Rotor - Some people in the comments suggested to try and use a double rotor. This will increase the magnetic field produced by the neodymium magnets and therefore will also increase the motor's torque. But in practice this was not the case and it barely had any effect. The measured torque was 0.9gcm (the same as with one rotor).
Ferrite Sheet - This was used as a core to increase the strength of the magnetic field inside the printed windings. Two different shaped cores were tested. The uncut one gave a higher torque value and has increased it from 0.9gcm to 1.5gcm. The only down side of this is that It has also increased the pcb's temperature from 70°C to 90°C due to eddy current losses.
Delta configuration - Other simple way to increase the torque is by changing the configuration to a delta winding. This way the coils will be powered with a higher voltage, so it will also increases the torque and temperature (hopefully not by much). This approach was not tested yet.
Increase the winding's magnetic field strength by reducing the PCB thickness
Use ceramic instead of stainless steel bearings to reduce friction
Experiment with different trace winding's clearance and thickness. Increasing it to 5/5mil from 4/4mil will reduce the pcb's cost at low volumes. However, this would also enlarge the motor's diameter to reach same parameter's of the 40turn 4/4mil coil.
My plan for speed controlling the PCB Motor was to implement a sensorless back-emf speed controller, which works just like every other brushless ESC. It measures the time it takes to detect the zero-crossing point from the under-driven phase, and adjust the commutation waveforms according. However, during testing the back-emf generated in the windings of the PCB motor was a little weak.
Plan-B is to use a hall sensor to implement the closed loop speed controller. This will be a little more pricey but will also include positional sensing.
This project started with me trying to design a small cheap drone. Dc brushed motors are typically used for micro-drone designs since they are much cheaper than brushless motors. But these motors were not compact enough for my application. So I started looking into ways to make a custom brushless motors which is smaller, cheaper and easier to manufacture.
A normal outrunner
brushless motor is made from a stator, a rotor and a shaft that connects the
two via a bearing. Its stator has windings around an iron core to
rotate the magnets on the rotor. The high magnetic permeability of the iron
core creates a strong magnetic field around each coil, which improves the motor's
I had this idea of making the stator embeeded in the PCB itself. My only concern was that to make it small, it had to be core-less. I decided to try it out and see if it had
enough strength to rotate a small propeller (spoilers - it did).
I wanted the first prototype to have the best possible chance of working, while still being as small as possible. So I set the trace spacing and thickness to 0.1mm and the via's drill size to 0.15mm. Although these parameters would increase the manufacturing costs of the PCB, it was the safest starting point for my PCB motor design.
I decided to make my motor have a 4-layer 6-pole stator, to have as many windings as possible. The star type stator configuration was used to limit the phase voltage, hence limiting the overall power of the motor (more power = more heating in stator coils).
There is alot more of experimentation and testing that I need to do before trying to integrate it with a drone. I want to find the best "turns-to-size" ratio and how does that effect the motor's torque. I would also like to test the delta configuration and a PCB-motor with a 9-pole stator.