Magnetic levitation - what is it and how is it possible. Do-it-yourself Levitron with a controlled suspension How to make an electro-magnetic levitating mechanism yourself

Levitation(from lat. Levitas"lightness, lightness") - a physical phenomenon in which an object without visible support soars in space without touching a solid surface. People often associate this phenomenon with magic, ghosts, UFOs and other incredible phenomena.
On the other hand, levitation is a relatively simple physical phenomenon for metallic objects in a magnetic field.

I suggest you familiarize yourself with the device designed for levitation of metal objects. The principle of operation is simple. In order for an object to hang in space, instead of a permanent magnet, it is necessary to use an electromagnet controlled by an electronic circuit in such a way that a metal object seems to hover at a certain distance from the electromagnet. The position of an object in space is monitored by an optical pair, which consists of an infrared photo and LEDs. If the object rises too high, then the photodiode will be less illuminated - the current through the electromagnet winding will decrease and its attractive force will also decrease. If the object falls too low, the photodiode will be more illuminated, the current through the electromagnet winding will increase, and its attractive force will increase.

Rice. 1 Scheme of the electromagnetic levitation device

The control scheme magnetic levitation devices(Fig. 1) uses a 1458 or 4558 operational amplifier (op amp) and a powerful MOSFET with a heat sink. The reference voltage is taken from the divider R3-R4 and fed to the non-inverting input 3 of the op-amp. The controlled voltage is supplied from the divider R2-VD2 to the input 2 of the OU. With a slight change in voltage at R2-VD2, a mismatch signal appears, which is repeatedly amplified and changes the voltage across transistor VT1.

An electromagnet can be wound on the frame of a large old relay. The coil contains 1200 turns of wire with a diameter of 0.4-0.5 mm. The iron core has a diameter of 8-10 mm.

There are no special criteria for the photodiode used, you can use the model that you have at hand. But since their characteristics differ, the resistor R1 adjusts the precise operation of the circuit for the given parameters of the photodiode.

If you have problems with the stability of the device (the object vibrates), then you may need to change the time constant of the loop. To do this, it is necessary to experimentally select the value of the capacitor C1, from 22 microfarads to 1 microfarads, until the circuit starts to work stably.

The idea of ​​this lesson was inspired by the project of the Kickstarter crowdfunding platform called "Air Bonsai", a really beautiful and mysterious project that was made by the Japanese.

But any riddle can be explained by looking inside. In fact, this is magnetic levitation, when there is an object levitating from above, and an electromagnet controlled by a circuit. Let's try together to realize this mysterious project.

We found out that the circuit of the Kickstarter device was quite complex, without any microcontroller. There was no way to find its analog circuitry. In fact, if you look more closely, the principle of levitation is quite simple. We need to make a magnetic part "floating" above another magnetic part. The main further work was to ensure that the levitating magnet did not fall.

There was also the suggestion that doing this with an Arduino is actually a lot easier than trying to figure out the schematics of a Japanese device. In fact, everything turned out to be much simpler.

Magnetic levitation consists of two parts: a base part and a floating (levitating) part.

Base

This part is at the bottom, which consists of a magnet to create a circular magnetic field and electromagnets to control this magnetic field.

Each magnet has two poles: north and south. Experiments show that opposites attract and like poles repel. Four cylindrical magnets are placed in a square and have the same polarity, forming a circular magnetic field upwards to push out any magnet that has the same pole in between.

There are four electromagnets in general, they are placed in a square, two symmetrical magnets are a pair and their magnetic field is always opposite. The Hall effect sensor and circuit control the electromagnets. We create opposite poles on electromagnets by current through them.

floating part

The item includes a magnet floating above the base that can carry a small plant pot or other items.

The top magnet is lifted by the magnetic field of the bottom magnets, because they have the same poles. However, as a rule, it tends to fall and pull towards each other. To prevent the top of the magnet from flipping over and falling off, the electromagnets will create magnetic fields to push or pull to balance the floating part thanks to the Hall effect sensor. The electromagnets are controlled by two X and Y axes, whereby the top magnet is kept balanced and floating.

Electromagnets are not easy to control and require a PID controller which is discussed in detail in the next step.

Step 2: PID controller (PID)

From Wikipedia: "Proportional-integral-derivative (PID) controller is a device in a control loop with feedback. It is used in automatic control systems to generate a control signal in order to obtain the necessary accuracy and quality of the transient process. The PID controller generates a control signal that is the sum three terms, the first of which is proportional to the difference between the input signal and the feedback signal (error signal), the second is the integral of the error signal, the third is the derivative of the error signal.

In simple terms: “The PID controller calculates the “error” value as the difference between the measured [Input] and the desired setting. The controller tries to minimize the error by adjusting [output]."

So, you tell the PID what to measure (Input), what value you want and a variable that will help to have this value at the output. The PID controller then adjusts the output to make the input equal to the setting.

For example: in the car we have three values ​​​​(Input, Set, output) will be - speed, desired speed and angle of the gas pedal, respectively.

In this project:

1. The input is a real-time current value from the hall sensor, which is updated continuously as the position of the floating magnet will change in real time.
2. The setpoint is the value from the hall sensor that is measured when the floating magnet is in the balance position, at the center of the base of the magnets. This index is fixed and does not change over time.
3. The output signal is the speed to control the electromagnets.

Thanks to the Arduino community for writing a PID library that is very easy to use. More information about the Arduino PID can be found on the official Arduino website. We need to use a pair of PID controllers under the Arduino, one for the X axis and one for the Y axis.

Step 3: Accessories

The list of components for the lesson is decent. Below is a list of the components you should buy for this project, make sure you have everything before starting. Some of the components are very popular and you will probably find them in your own warehouse or at home.

Step 4: Tools

Here is a list of the tools most commonly used:

• soldering iron
• Hand saw
• multimeter
• Drill
• Oscilloscope (optional, you can use a multimeter)
• Bench drill
• Hot glue
• Pliers

Step 5: LM324 Op-amp, L298N driver and SS495a

LM324 Opamp

Operational amplifiers (op-amps) are among the most important, widely used and versatile circuits in use today.

We use an op amp to amplify the signal from the hall sensor, the purpose of which is to increase the sensitivity so that the arduino can easily recognize a change in the magnetic field. A change of a few mV at the output of the hall sensor, after passing through the amplifier, can change by several hundred units in the Arduino. This is necessary to ensure smooth and stable operation of the PID controller.

The common op amp we chose is the LM324, it's cheap and you can buy it at any electronics store. The LM324 has 4 internal amplifiers which allow for flexible use, however this project only needs two amplifiers, one for the X axis and one for the Y axis.

Module L298N

The L298N double H-bridge is usually used to control the speed and direction of two DC motors, or drive one bipolar stepper motor with ease. The L298N can be used with motors from 5 to 35 VDC.

There is also a built-in 5V regulator, so if the supply voltage is up to 12V, you can also connect a 5V power supply from the board.

This project uses the L298N to drive two pairs of electromagnet coils and uses the 5V output to power the Arduino and the hall sensor.

Module pinout:

• Out 2: pair of electromagnets X
• Out 3: a pair of electromagnets Y
• Input power: DC 12V input
• GND: Ground
• Output 5v: 5v for Arduino and hall sensors
• EnA: Enable PWM signal for output 2
• In1: Enable for output 2
• In2: Enable for Out 2
• In3: Enable for output 3
• In4: Enable for output 3
• EnB: Enable PWM signal for Out3

Connecting to Arduino: We need to remove 2 jumpers on pins EnA and EnB, then connect 6 pins In1, In2, In3, In4, EnA, EnB to Arduino.

SS495a Hall sensor

SS495a is a linear hall effect sensor with analog output. Please note the difference between analog output and digital output, you cannot use a sensor with digital output in this project, it only has two states 1 or 0, so you cannot measure the output of magnetic fields.

An analog sensor will result in a voltage range of 250 to Vcc, which you can read using the Arduino's analog input. To measure the magnetic field in both the X and Y axes, two Hall sensors are required.

Step 6: Neodymium NdFeB (Neodymium Iron Boron) Magnets

From Wikipedia: "Neodymium is a chemical element, a rare-earth metal of silver-white color with a golden hue. It belongs to the lanthanide group. It oxidizes easily in air. It was discovered in 1885 by the Austrian chemist Karl Auer von Welsbach. It is used as a component of alloys with aluminum and magnesium for aircraft - and rocket science.

Neodymium is a metal that is ferromagnetic (in particular, it exhibits antiferromagnetic properties), which means that, like iron, it can be magnetized to become a magnet. But its Curie temperature is 19K (-254°C), so in its purest form, its magnetism only shows up at extremely low temperatures. However, compounds of neodymium with transition metals such as iron can have Curie temperatures well above room temperature, and these are used to make neodymium magnets.

Strong is a word used to describe a neodymium magnet. You cannot use ferrite magnets because their magnetism is too weak. Neodymium magnets are much more expensive than ferrite magnets. Small magnets are used for the base, large magnets for the floating/levitating part.

Attention! You need to be careful when using neodymium magnets, as their strong magnetism can harm you, or they can break data on your hard drive or other electronic devices that are affected by magnetic fields.

Advice! You can separate two magnets by pulling them horizontally, you cannot separate them in the opposite direction because their magnetic field is too strong. They are also very fragile and break easily.

Step 7: Prepare the base

We used a small terracotta pot, which is usually used for growing succulents or cactus. You can also use a ceramic pot or a wooden pot if they are suitable. Use an 8mm drill to create a hole in the bottom of the pot that is used to hold the DC socket.

Step 8: 3D Print the Floating Part

If you have a 3D printer, great. You have the ability to do everything with it. If there is no printer - do not despair, because. you can use a cheap 3D printing service which is very popular right now.

For laser cutting, the files are also in the archive above - the AcrylicLaserCut.dwg file (this is autocad). The acrylic part is used to support the magnets and electromagnets, the rest is used to cover the surface of the terracotta pot.

Step 9: Preparing the SS495a Hall Sensor Module

Cut the PCB layout into two pieces, one piece to attach the hall sensor and the other to the LM324 circuit. Attach two magnetic pickups perpendicular to the PCB. Use thin wires to connect the two pins of the VCC sensors together, do the same with the GND pins. Output contacts separately.

Step 10: Op-amp Circuit

Solder the socket and resistors to the PCB following the diagram, paying attention to place the two potentiometers in the same direction for easier calibration later. Connect the LM324 to the jack, then connect the two outputs of the hall sensor module to the op-amp circuit.

Connect the two output wires of the LM324 to the Arduino. 12V input to 12V input of L298N module, 5V output of L298N module to 5V potentiometer.

Step 11: Assembling the Electromagnets

Assemble the electromagnets on the acrylic sheet, they are fixed in four holes near the center. Tighten the screws to avoid movement. Because the electromagnets are symmetrical at the center, they are always at opposite poles, so that the wires on the inside of the electromagnets are connected together, and the wires on the outside of the electromagnets are connected to the L298N.

Run the wires under the acrylic sheet through the adjacent holes to connect to the L298N. The copper wire is covered with an insulating layer, so you must remove it with a knife before you can solder them together.

Step 12: Sensor Module and Magnets

Use hot glue to fix the sensor module between the solenoids, note that each sensor must be square with two solenoids, one on the front and one on the back. Try to calibrate the two sensors as centrally as possible so they don't overlap, which will make the sensor the most efficient.

The next step is to assemble the acrylic based magnets. By combining two D15*4mm magnets and a D15*3mm magnet together to form a cylinder, it will cause the magnets and electromagnets to be the same height. Assemble the magnets between pairs of electromagnets, note that the poles of the ascending magnets must be the same.

Step 13: DC Power Connector and L298N 5V Output

Solder the DC power jack with two wires and use heat shrink tubing. Connected the DC power connector to the input of the L298N module, its 5V output will supply power to the Arduino.

Step 14: L298N and Arduino

Connect the L298N module to the Arduino following the diagram above:

L298N → Arduino
5V→VCC
GND → GND
EnA → 7
B1 → 6
B2 → 5
B3 → 4
B4 → 3
EnB → 2

Step 15: Arduino Pro Mini Programmer

Since the Arduino pro mini does not have a USB to serial port, you will need to connect an external programmer. FTDI Basic will be used to program (and power) the Pro Mini.

1. Brief description

It turned out this:

2.Functional diagram

Electromagnetic sensors located at the ends of the coil produce a voltage proportional to the level of magnetic induction. In the absence of an external magnetic field, these voltages will be the same regardless of the magnitude of the coil current.

If there is a permanent magnet near the lower sensor, the control unit will generate a signal proportional to the field of the magnet, amplify it to the desired level and transmit it to the PWM to control the current through the coil. Thus, feedback occurs and the coil will generate such a magnetic field that will keep the magnet in balance with the forces of gravity.

Something abstruse everything turned out, I'll try it differently:
- There is no magnet - the induction at the ends of the coil is the same - the signal from the sensors is the same - the control unit gives the minimum signal - the coil works at full power;
- They brought the magnet close - the induction is very different - the signals from the sensors are very different - the control unit gives out the maximum signal - the coil turns off completely - no one holds the magnet and it starts to fall;
- Beckons falls - moves away from the coil - the difference in signals from the sensors decreases - the control unit reduces the output signal - the current through the coil increases - the induction of the coil increases - the magnet begins to attract;
- Beckons is attracted - approaches the coil - the difference in signals from the sensors increases - the control unit increases the output signal - the current through the coil decreases - the induction of the coil decreases - the magnet begins to fall;
- A miracle - the magnet does not fall and is not attracted - or rather, it falls and is attracted several thousand times per second - that is, a dynamic balance arises - the magnet simply hangs in the air.

3.Design

78 meters of copper enameled wire with a diameter of 0.6 mm are tightly wound on a D36x48 plastic frame, about 600 turns. According to calculations, with a resistance of 4.8 ohms and a power supply of 12V, the current will be 2.5A, the power will be 30W. This is necessary for the selection of an external power supply. (In fact, it turned out to be 6.0 Ohm, they hardly cut more wire, rather saved on the diameter.)

A steel core from a door hinge with a diameter of 20 mm is inserted inside the coil. Sensors are fixed at its ends with hot glue, which must be oriented in the same direction.

The coil with sensors is mounted on an aluminum strip bracket, which, in turn, is attached to the housing, inside which is the control board.

On the case there is an LED, a switch and a power socket.

The external power supply (GA-1040U) is taken with a power reserve and provides current up to 3.2A at 12V.

An N35H magnet D15x5 with a glued Coca-Cola can is used as a levitating object. I must say right away that a full jar is not good, so we make holes at the ends with a thin drill, drain a valuable drink (you can drink if you are not afraid of chips) and glue a magnet to the top ring.

4.Schematic diagram

The signals from the sensors U1 and U2 are fed to the operational amplifier OP1 / 4, connected according to the differential circuit. The upper sensor U1 is connected to the inverting input, the lower U2 is connected to the non-inverting one, that is, the signals are subtracted, and at the output OP1 / 4 we get a voltage proportional only to the level of magnetic induction created by the permanent magnet near the lower sensor U2.

The combination of elements C1, R6 and R7 is the highlight of this scheme and allows you to achieve the effect of complete stability, the magnet will hang in its tracks. How it works? The DC component of the signal passes through the divider R6R7 and is attenuated by 11 times. The variable component passes through the C1R7 filter without attenuation. Where does the variable component come from? The constant part depends on the position of the magnet near the lower sensor, the variable part arises due to the oscillations of the magnet around the equilibrium point, i.e. from a change in position in time, i.e. from speed. We are interested in the fact that the magnet is stationary, i.e. its speed was equal to 0. Thus, in the control signal we have two components - the constant is responsible for the position, and the variable is responsible for the stability of this position.
Further, the prepared signal is amplified by OP1/3. With the help of a variable resistor P2, the necessary gain is set during the tuning phase to achieve equilibrium, depending on the specific parameters of the magnet and coil.

A simple comparator is assembled on OP1 / 1, which turns off the PWM and, accordingly, the coil when there is no magnet nearby. A very convenient thing, you do not need to remove the power supply from the outlet if the magnet is removed. The trigger level is set by the variable resistor P1.

Next, the control signal is applied to the pulse-width modulator U3. The output voltage range is 12V, the frequency of the output pulses is set by the values ​​of C2, R10 and P3, and the duty cycle depends on the level of the input signal at the DTC input.
The PWM controls the switching of the power transistor T1, which in turn controls the current through the coil.

The LED1 LED can not be installed, but the SD1 diode is necessary to drain excess current and avoid overvoltage at the moments when the coil is turned off due to the phenomenon of self-induction.

NL1 is our homemade coil, which is dedicated to a separate section.

As a result, in equilibrium mode, the picture will be something like this: U1_OUT=2.9V, U2_OUT=3.6V, OP1/4_OUT=0.7V, U3_IN=1.8V, T1_OPEN=25%, NL1_CURR=0.5A.

For clarity, I apply graphs of the transfer characteristic, frequency response and phase response, and oscillograms at the output of the PWM and coil.

5. Choice of components

As magnetic field sensors U1 and U2, SS496A analog Hall sensors with a linear characteristic up to 840 gauss are used, this is the very thing for our case. When using analogs with a different sensitivity, you will need to adjust the gain by OP1 / 3, as well as check for the level of maximum induction at the ends of your coil (in our case, with a core, it reaches 500 gauss), so that the sensors do not saturate at peak load.

OP1 is LM324N quad op amp. When the coil is off, it gives out 20mV instead of zero at output 14, but this is quite acceptable. The main thing is not to forget to choose from a bunch of 100K resistors the closest in actual value for installation as R1, R2, R3, R4.

Ratings C1, R6 and R7 were selected by trial and error as the best option for stabilizing magnets of different calibers (N35H magnets D27x8, D15x5 and D12x3 were tested). The R6 / R7 ratio can be left as is, and the value of C1 can be increased to 2-5 microfarads, in case of problems.

When using very small magnets, you may not get enough gain, in which case cut the value of R8 to 500 ohms.

D1 and D2 are ordinary 1N4001 rectifier diodes, any will do here.

The common TL494CN chip is used as a pulse-width modulator U3. The operating frequency is set by the elements C2, R10 and P3 (according to the 20 kHz scheme). The optimal range is 20-30 kHz, at a lower frequency coil whistle appears. Instead of R10 and P3, you can simply put a 5.6K resistor.

T1 is an IRFZ44N field effect transistor, any other from the same series will do. When choosing other transistors, it may be necessary to install a radiator, be guided by the minimum values ​​​​of the channel resistance and gate charge.
SD1 is a VS-25CTQ045 Schottky diode, here I grabbed it with a large margin, a regular high-speed diode will do, but it will probably get very hot.

LED1 yellow LED L-63YT, here, as they say, the taste and color, you can set them up a little more so that everything glows with multi-colored lights.

U4 is a 5V voltage regulator L78L05ACZ to power the sensors and the op-amp. When using an external power supply with an additional 5V output, you can do without it, but it is better to leave the capacitors.

6.Conclusion

7. Disclaimer

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In this article, Konstantin, the How-todo workshop, will show us how to make a levitron.

So, levitron. The principle of operation of this pribluda is simple, like a self-tapping screw. We use an electromagnet to lift a piece of some magnetic material into the air. To create the effect of soaring, the electromagnet is turned on and off with a high frequency.

That is, as it were, we lift and throw a magnetic sample.

The scheme of such a device is surprisingly simple, and it is not difficult to repeat it. Here is the schematic.

Hall sensor, I have this A3144, it can also be replaced with a similar one.
Copper winding enameled wire with a diameter of 0.3 0.4 mm, 20 meters. The author has a wire of 0.36 mm.

Let's move on to assembly. First you need to make a cardboard coil for the body of the future electromagnet.
The coil parameters are as follows:
6 mm diameter of the inner sleeve, the width of the winding layer is approximately 23 mm and the diameter of the cheeks, with a margin, is about 25 mm.