How to print an electric motor
The axial magnetic flux motor uses printed boards on the printer as electromagnetic coils
Translation of the article from spectrum.ieee.org by Carl Bugeja
It all started with the fact that I wanted to make a very small drone. But I quickly realized that one factor limits attempts to reduce and facilitate the project: motors. Even small motors are separate objects that need to be connected to all other electronics and structural elements. So I began to think about a way to merge these elements to save weight.
I was inspired by the fact that some radio systems use antennas, which are copper tracks on a printed circuit board. Is it possible to use something like this to create a sufficiently strong magnetic field capable of feeding the motor? I decided to see if I could create an axial magnetic flux motor with electromagnetic coils, executed in the form of tracks on a printed circuit board. In the axial magnetic flux motor, the electromagnetic coils forming the stator are attached parallel to the rotor, which is made in the form of a disk. Permanent magnets are integrated in the rotor disk. Feeding the alternator to the stator coils causes the rotor to rotate.
brushless motor A control electronics with a feedback system is required.
In each layer of the circuit there is a set of coils, and they are stacked one on top of the other, linking together and forming continuous tracks.
The final four-layer printed circuit board
The pulses of these coils rotate the rotor printed on the 3D printer, into which permanent magnets are built.
The system is not as powerful as a traditional brushless motor, but printed circuit boards are cheaper and lighter than
In the previous model of the motor I created, I used the counter-emf as feedback for speed control. The anti-emf is obtained due to the fact that the rotating motor works as a generator, creating a voltage in the stator coils, counteracting the voltage rotating the motor. The information on the counter-emf provides feedback informing about the rotation of the motor, and allows the control electronics to synchronize the coils. But in my motor with printed circuit boards the counter-emf was too weak to be used. So I mounted on it. Hall sensor , directly measuring the change in the magnetic field, in order to measure how quickly the rotor and its permanent magnets rotate above the sensor. This information goes into the motor control electronics.
To make the rotor, I turned to 3D printing. Initially, I made a rotor that solidified on a separate metal rod, but then I just started typing and the rod as an integral part of the rotor. This reduced the number of physical components to the rotor, four permanent magnets, a bearing and a printed circuit board that provides both coils and structural strength.
Soon my first motor already worked. Tests have shown that it stably provides a static torque of 0.9 g * cm. This point was not enough to implement my original plan for creating an integrated motor for the drone, but I thought that such a motor can still be used as an engine for small and cheap robots moving on the ground on wheels, so I continued to research (usually the motors turn out to be the most expensive parts of robots). The printed motor can work with a voltage of 3.5 to 7 V, although at a high voltage it is sensibly heated. At 5 V, its operating temperature is 70 ° C, which is quite acceptable. It consumes about 250 mA.
At the moment I am concentrated on increasing of the torque. I managed to almost double it by adding a ferrite sheet to the rear of the stator coils to limit the magnetic field lines. I also plan other prototypes of motors with other winding systems. In addition, I'm working on using the same technologies to create linear drive , capable of moving the printed slider along a series of 12 coils. Also I'm testing a prototype of a flexible PCB using the same coils. My goal is to start making new robots using smaller and cheaper mechanisms than those available today.
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