My open source PCB motor is my attempt to build 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.
It also has a 16mm diameter, 1.7mm thin 3d printed 4-pole rotor. So the total thickness of this axial flux motor adds up to 5mm (excluding the shaft) and weighs 1.5 grams.
The inspiration for this idea came from trying to build smaller and cheaper drone. Making the motor onto the PCB itself will reduce the overall price of any tiny robot, allowing swarm robotics to become more affordable.
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.
My SUPER tiny 6-layer PCB Motor is spinning! Here's the full video describing how I designed it:
My original 4-layer PCB motor had a 16mm diameter. By adding two extra layers I was able reduce the number of turns per layer and get it to 11mm. The total height of the motor is 3.6mm and its weight is 0.5 grams.
No space is lost in this pcb! Each coils have 3 vias to connect the in-between layers. These forced a triangular shaped stator poles, which utilize the magnetic field area more efficiently.
The tiny rotor design has four press-fit 2mm n52 magnets and a 3mm bearing. This new design has the shaft soldered onto the stator, so it is fixed and don't rotate with the rotor.
I had chosen to go with this design because of two things:
1. I couldn't find a bearing small enough to fit in the middle of the stator. 2.I'm not planning to use a shaft. Customized 3d-printed rotors makes much more sense.
The phase resistance of this motor was measured to be 15ohmsand its getting to 85℃ with a 4V supply, so it should be perfect for a 1s lipo.
This video shows how i designed my PCB Motor's ESC and what where the challenges involved in getting my speed controller to work.
This is its schematics:
It has a PIC16F1503 as the main controller and a triple half bridge driver STSPIN230, to control the three phases of the motor. These are both powered from the same supply, to avoid having an extra power wire or on-board regulator, reducing the cost even further. I filtered the digital circuitry supply from an LC filter to attenuate any noise the motor can generate. It can operate from a 5V to 2.6V supply and draws around 220mA in total.
As i explained in my previous project logs, the back emf generated from my pcb motor was too weak to implemented a sensorless speed controller. So i decided to use a hall sensor to provide feedback to the microcontroller and then implemented a speed closed loop speed controller.
The open source gerber files and schematics for this PCB are available for download.
In the beginning of November I will be giving a demo of this project at the Hackaday Superconference so see you there!
I have finally finish my PCB Motor with the integrated ESC! Made this quick video showcasing it:
The PCB was hand soldered. It took me a little while to get it to work because I had some soldering flux residue on one of the motor driver chip that was acting as impedance. This was triggering the driver's on-board protection circuit. But after removing the chip and clean its pads, it was up and running.
I have managed to fit the ESC in such a small area by soldering parts on both sides of the PCB and using the smallest footprints I could find! Both the MCU and motor driver have a 3x3mm qfn package and most of the other discrete components are 0201s!
I'm currently making another video explaining how i design this driver and what were the challenges involved! So I will be releasing its schematics and gerber files in the next few days :)
I love designing electronics that fit in very tiny space. My 4-layer brushless PCB Motor is currently 16mm in diameter. So how can I make it smaller?
This 16mm design is already pushing the limits by having 4mils (0.1mm) track width and clearance. Using thinner pcb traces is possible, but would make its price (for prototyping) explode. My intent is to make this open source motor accessible to others, so it doesn't makes much sens to go in this direction. So I'm sticking to 4/4mil traces.
My motor has around 40 turns, so going much lower than that would make the coils too inefficient and the pcb would heat up way to much. Based on a my pcb coils tests the minimum number of turns for 4mil should be 40 turns and for 5mil it should be 60 turns, not to exceed 70°C with a constant (100% duty cycle) supply.
The only remaining option to try and make it smaller, is to increase the number of layers to decrease the number of turns per layer. The current design has 10 turns per layer, so for this tiny 6-layer motor I decided to go for 6 turns per layer, having a total of 36 turns. Setting a tight clearance of 4mil, the total diameter of the motor end up being 11mm.
The extra two layer, increased the number of vias in the middle of each coil to three. This naturally formed the spiral to have a triangular shape which use the area of the magnetic field more efficiently.
Another natural advantage of using a 6-layer pcb, is that the thickness between each layer is much smaller which increases the magnetic field strength.
For this design I had to make some changes on the rotor, because I couldn't find a bearing small enough to fit at the center of the pcb (smallest bearing available is 2mm). So what i decided to do is extended a stationary-shaft from the pcb, and connect the bearing on the rotor. I'm still designing the 3d-printed part, so I will post more info on that soon.
I have just ordered this 6-layer pcb motor from JLCPCB which were kind enough to sponsor this design.