The engine remains the most widespread electric motor. In smaller apartment there are at least a dozen refrigerator, vacuum cleaner, washing machine, record players, tape recorders, children's toys, camera, etc.. It presents the piston engine two major advantages: it runs smoothly and does not emit any smoke.
By cons, he must bring the current, and it often seems much less easy to understand. Yes, the electric motor can be set, shunt, synchronous, asynchronous, single phase, three phase, step-by-step, self-synchronous and so on. In fact, as we shall see, the principle is relatively simple but results in many variations.
In this section, we have built electric motors of various kinds, but this time we chose an extreme solution: the absolute simplicity. With the inventive talent of Peter Courbier, one could reach a record: the engine can be constructed from a tin can and a few strands of copper wire. This means that its components are available to all for a ridiculous price, and in addition it presents no difficulty mounting.
This does not prevent it from working perfectly, and clearly illustrate the principle is the basis of any electric motor: the attraction or repulsion of magnetic fields generated by current flow in one thread. We know that a magnet attracts an iron ring or a piece of nickel 5 F, we can exploit this force to maintain a closed door or to hold papers on a wall of sheet steel, but not an effort to give DC: Once the piece of steel came to stick to the magnet, it stays there and you have to spend an equal energy to take off.
Going a little further in life skills: everything has a magnet pole (+) pole and (-), known generally north and south poles of opposite signs attract each other (with much more force they n 'draw a room neutral) and two poles repel. To exploit these forces and transform them into driving forces should be able to cut and restore the magnetic field, otherwise, we have seen, the poles come into contact and do not move.
Luckily, the Danish Oersted in 1819 made a discovery that led to the electric motor: the flow of current in a wire moves the needle of a compass placed nearby, ie the current (the direction of movement of electric charges ) generates a magnetic field exactly like the one that exists around a magnet. By multiplying the drivers on the same portion of space, we multiply the field strength, hence the simple idea of rolling in a long spool thread
Such a coil is an electromagnet, and as the current circulates it has the same properties as a bar magnet: it has a pole (+) pole and (-) that can be reversed by changing the direction of current draws everything in iron, nickel or cobalt, or which is already magnetized and opposite sign to him - and he rejects what is the same sign. But as soon as the current stops, the coil becomes, in terms of the magnetic equivalent of a stick.
With a switch, a coil is therefore a magnet that can turn on and off at will, it does not take more to an electric motor. To begin, we'll stick a pin through a first coil: it will be the drive shaft; then we put a second coil fixed near the first, and it sends the current in both. This created two magnets whose attractions or repulsions will come into play
If there is attraction, the coil rotates on its axis to be closer to the fixed coil, otherwise it will be delayed, but it will still be turned on its axis: in both cases, there are beginnings of a rotation. The whole problem now will be to maintain it. Note first that the second case reduces itself to the first: when the pole, say North, is pushed in and turned away from the north pole of the fixed coil, the rotation takes the same time moving towards the south Fixed the north and attraction comes in.
She also will continue as long as the operator will not be tired of cutting and reversing the current every half turn. Note at once a thing for the engine is running, it is necessary that the rotor (moving coil) is supplied by a current periodically reversed, so by definition an alternating current. No, in the true sense of DC motor - the two opposite poles of the coils remain face to face and not moving.
Of course, we can dispense with the operator and handling of switches, otherwise the engine would have no future. It is immediate that the voice coil can be connected directly to the power source by a wire as it would be immediately broken and twisted by the rotation of the reel. We must therefore take the current to the shaft with wipers that will support on conductors connected to the coil.
However, these rubbers, called brushes, are of themselves solve the problem very simply the interruption and reversal of the current every half turn. Our coil carrying a line obviously has an input wire, a lead wire two son will be bonded along both sides of the axis, and two other drivers fixed (the blades) will come rub two diametrically opposite points on this axis.
If the rotor turns, there comes a time when the brushes touch the son of two voice coil, it becomes magnetized and accelerates the onset of rotation, then stop the brushes touch the son and the rotor continues its momentum. Again the son will be back in contact with the brushes, but in opposite ways: the broom that affected the left thread, for example, now affects one on the right, and vice versa.
To make our engine, a simple tin and copper wire will do.
As a result, the current flows in opposite directions in the voice coil and magnetic attractions drive the rotor on another half turn. The current is again interrupted and reversed at the end of this turn, and the cycle continues until the engine is on. But generally simplified as a vehicle does not start by itself, unless the brooms are fortunately in contact with the son of the rotor. Otherwise, it must be launched by hand.
To start one, it is not one, but at least three coils around the axis, and three contacts which will focus on the two brushes - at that time, the coil is energized is always a little behind the fixed coil and is drawn (or pushed) by it, which initiates the rotation. In practice, there is still much more to the rotor windings (5, 7, ... 11 ... 23, etc.). To ensure that walking is perfectly fluideQuant the collector, it consists of copper plates on which rub coal. You can also feed directly into the windings fixed AC, which provides the collector and brushes whose primary role is to feed the rotor with alternating current. The operating principle remains the same, but for a good performance should be considered a large number of factors (voltage, current, field effective action of magnetic fields created, resistance of the circuits, etc.)..
A good electric motor, however small, requires extensive preliminary studies and much experience. Whatever we build will lead us hopefully not so far away, yet he is running. It all starts with the search component, which will be quick since it is sufficient to obtain a tin tin and enameled wire coil 5 / 10 or 6/10mm.
We find the copper wire in electronics dealers, but you can also get it from an old radio or other processor. For the can, it is best to choose a box of 1 kg, and check (with a magnet if necessary) it is made of sheet steel - aluminum, paramagnetic, add nothing to the performance of the machine. To cut the tin, an old pair of scissors should (a new one too, but it only remains to sharpen it then).
After cutting the box to extract the cylindrical part and having picked up carefully, we can remove the prints that adorn it with a solvent (acetone, trichlorethylene). In fact, they can leave and move closer to the real engines of which the plates are separated from each other by an insulating film to eliminate eddy currents.
Two engine versions are available: - rustic style mounted on a board of cons-plated 90 x 80mm on which the various components (bearings, brushes, etc..) Will be fixed with simple bugs. - The version of "luxury" whose base is formed by a thick piece of cardboard the same coast, but that will use terminal strips instead of bugs.
The base, figure 1, as the case may be made by a rectangle of cardboard or plywood against the 90 x 80mm. Levels are illustrated in Figure 2, the line on the sheet of tin will be done with a grease pencil to the ribs shown in the figures. To fold the sheet at right angles, the help of a template (rectangular box of some sort). The holes for the passage of the rotor axis will be obtained by drilling with a sewing needle. After cutting two rectangles of 25 x 55mm, they pierce and bend the ribs shown in Figure 2.
The rotor is described in Figures 3 to 6. The axis of the rotor consists of a steel rod about 1 mm in diameter and 40mm (or more) in length. A sewing needle of the same diameter appropriate if we can get the piano wire - available in specialist models. The rotor core is formed by stacking rectangles of tin as seen in Figures 3-6.
The six small rectangles of tin (10 x 24mm) arranged on either side of the axis are sandwiched between two large rectangles (10 x 50mm). This stack finished section should look as shown in Figure 3. Each slide is glued with adhesive cyanoacrylate gel, plus the passage of the shaft. We can help the jaws of a vise to flatten the core before the bonding, but it is not essential.
We end by wrapping around a piece of tape - Figure 4: without this precaution, the coating that insulates the copper wire could be scratched by sharp angles and this may cause short circuits. Putting such a stack of laminated sheets in the coil can concentrate the magnetic field of the current and meet all the forces of attraction or repulsion. All electric motors and high efficiency are wound around a soft iron sheet isolated from each other.
Figure 4 also shows how to proceed to wind 80 turns of copper wire 5/10mm contiguous turns on each side of the rotor and always in the same direction. At first, we will leave a 2cm length of wire (which will form the collector E) and from the axis, be wound 20 turns in the direction shown in Figure 4 on the way to one end. Then we will return to the center, another 20 towers, will be on the other side of the axis, and continue winding 20 turns to the other end, then we will return towards the axis by completing 20 laps remaining and cut off the wire, leaving 2 cm that will make the second collector ("S").
Then cut 5 plastic sleeves in a shaft of swab - see dimensions and other information in Figure 6. We will end the son of copper still wearing their insulating varnish in the sleeve 2 (2 mm long), then the son will go to the top of the sleeve 3 (5 mm long) and below the sleeve 4 (2 mm long) and finally they will be cut and folded as shown in Figure 6.
Only then we strip the outer part of the son of copper that will serve as a collector and will be in contact with the brushes.
For this we will remove the varnish by scraping with a fine blade cutter, this is essential and must be done with great care. Muff 1 (6mm) and 5 (1 mm) act as spacers. This will ensure that the rotor turns freely and without friction in its bearings.
The stator 7 to 9, is made and also for the same reasons a stack of plates with ribs and identification are given in Figure 7. A blade, angled 90 ° in U, is sandwiched between the plates B1 to B6 and C1 to C4, while the blades D1 x D2, bent on their bases, are used to fix the stator on its base.
As the rotor and for the same reasons, the portion of the nucleus (Figure 9) which is to receive the winding - up of 135 turns of enameled wire wound with touching turns 5/10mm in the same direction as the rotor - is coated with a layer of tape.
300mm long copper wire identical to that used for the windings used to make brooms - Figure 10. Incidentally, the blades of an electric motor must comply, in the case said, some constraints if you want to get a good running time. Their pressure on the collector must be sufficient to ensure contact, but not too much otherwise the mechanical wear in addition to slowing friction. We must also reckon with corrosion due to sparks.
This spring, properly regulated, will produce a constant pressure on the collector, despite the relative ductility of copper. If one has a terminal strip on the fix as mentioned in the same figure with adhesive neoprene.
Figure 11 shows how to be assembled and wired components we have manufactured. If we do not have terminal strips, brushes are fixed on the wooden base with thumbtacks. The stator and the bearing supports are glued to the base with glue-like neoprene or, at best, with pieces of tape.
One of the blades will be connected to the input coil of the stator by a splice obtained by twisting the bare son carefully. The other brush will go to one pole of the battery (4.5 V flat type), a paper clip will serve as a contact, while the output wire of the stator coil is connected to the other pole using the same kind of connection.
In the second case (deluxe version with terminal strip), wiring is identical. The strips are bonded with adhesive neoprene, and the stator and the bearing supports. We begin, therefore, battery not connected by glue the rear bearing support (neoprene) and then introduce the rotor shaft after having inserted the sleeves 1 and 5 (Figure 6).
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We will set up the stage earlier is to be maintained by a piece of tape. After that, we have and paste the stator (neoprene) ensuring its alignment and its centering relative to the rotor. Optionally, remove the branches of the U slightly so that the turning rotor does not touch him.
We then put the brushes mounted on their supports and adjusted carefully twist them slightly so that they support both sides of the cylindrical sleeve 3 which carries along two diametrically opposed the two generators son from the rotor. They stick (neoprene), taking care that the brushes do not intersect or touch.
Normally, when the rotor is horizontal, forming the collector's son should not be in contact with the brushes and such contact should occur just before the rotor is vertical (the result is that engine must be started to turn, but if by chance the rotor is in the position suitable).
This controlled, it will contact (any polarity) and the rotor will start gently. If the construction was carried out following the indications above, the engine must turn immediately. If this is not the case, we will take all stages by checking the winding direction and quality of contacts.
But if the result is positive, this does not mean it is the best possible speed can probably be improved. For this, we must adjust the pitch by varying the collector with tweezers (to the rigor of tweezers) the position of son. However, the theory and practice want these two son are still in the same plane passing through the axis.
It should play on the angle this plane with that of the coil, and proceed carefully. Those with a multimeter will help in this setting by measuring consumption. It will be optimal if a maximum speed, there is a minimum consumption (in milliamps).
When finished it can be useful to immobilize the collector with a trace of cyanoacrylate glue type, be careful that it does not overflow on the bare copper wire, or on the landing. There will not be to finish this engine, stick to the bearing support earlier and reflect on the construction of an identical but smaller.
Let us say immediately that to have an engine capable of starting one, the rotor must have 3 coils packed in 120 ° C - the current formula engine toys, but significantly complicates the construction. Of course, we can multiply the number of coils (5, 7, 11, 17, etc..) Rotor for a walk even more fluid, and also increase the number of stator windings. In any case, the principle is the same as our model ultra simplified. When we understand one, we understand all the others.
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