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Motor

Motor is «heart» of radio-controlled aircraft model and from its characteristics depends approximately 80% performance of aircraft model.

The smallest micro motor, that is affordable on offer is of course, Shicoh 2.8mm/3,2mm, and is placed in mobile phone «vibrik».

His highs are:

• easy to use (just we set voltage and it works)

• it has sufficiently firm metal case

• if the screw propeller is good selected it develops a static thrust up to 600-800 mg (milligram) by use one lithium cell (3,7V).

There are only two lows, but they are very essential:

• big weight (about 300mg)

• collector node, that too quickly outwears

The Shicoh device is out-of-the-way: rotor is winding in the form of a hollow cylinder (1) with an axel in the centre and collector on the one of its end. Stator (2) is produced from rare-earth (strong) magnet in the form of a cylinder with an aperture in the centre in which is pressed bronze bush. Magnet rotor is firm fixed in the vessel (3), stator on the contrary has free rotation round the rotor. Brush assembly is crowned the construction (4).


1

photo 1


Such type of motor is called COLLECTOR motor, the principle how it works is rather simple. Rotor, it was already said, is manufactured in form of hollow cylinder that consist of row windings (3 or 6 rows), these rows are connected as « delta» or «star» to the collector’s contacts.

 

By giving voltage on the brushes in two windings starts running current, that is produced magnet field displaced relative to stator’s field by 90 degrees, owing to what appears torque of shaft, it makes rotor rotate and with him collector thereby is ensuring right switching of windings, ipso facto, is ensuring permanent rotation of rotor (while the current is running).

 

Number of windings influences torque moment, in the six-windings version the torque moment is bigger.

 

 

Good alternative (for creative person) is radically different type of micro-motor with its unique properties.

 

It is called brushless or collectorless (CL), on your taste.

It is already clear from the name what defect it hasn’t , did you guess? Correct, it hasn’t the collector – element that is quick fray, therefore resource of such motor is very high and is limited practically only by bush quality.

 

The second important factor that forces you to choose this type of motor is its the least possible weight (it is limited only by imagination of constructor). The smallest specimen that I had seen in the network has weight 18mg (0.018gram!) and this together with the gear box! It is produced by modern «Levsha» that lives in Petersburg, Oleg Ladinskiy. The represented on photo 2 motor has weight 100mg and static traction 500mg.

Draw attention, the motor has minimally necessary components, nemaly:

Shaft (5), in our case it is drilling bit (diameter 0.26mm).

Bushes (6), out of fluoroolastic (or some other material).

Обмотки (7) Winding (7) actually this is one winding with two leads.

Shaft-rotor (8) out of rare-earth magnet.

And, of course, microchip (9), it replace collector assembly.

 

There is one more significant advantage: vast speed of rotation about 100 000! revolutions per minute, this is possible thanks to minimal friction (there is no collector assembly) and more, certainly thanks to presence only one phase (only one winding), but it isn’t rather advantage, but peculiarity of construction and principle of operation, but that’s not what we are about.

 

2

photo 2

 

 

So CL motor is more attractive? … We start doing it, then!

 

By without assistance making assemblies of micro-motor I shall try use the most affordable material.

Not everyone can afford yourself to buy the appropriate magnet for the stator, oh but we don’t need to buy, while we can accurately demount magnet out from «vibrik» (vibromotor) of your old mislaid, right for such case, mobile. By the way this is not only one detail that we can use out from «vibrik».

You need accurately pick off eccentric out from shaft. It is not difficult, we just grip eccentric in a vice and with power press out shaft by the help of the owl. If it not achieves results you can easy rap on owl with the small hammer. It comes good?

Keep on! Now our task is to lose brush assembly. Using the owl we unchuck «shackles» on the body, as it is shown on photo3

 

3

photo 3

 

After such operations the assembly easy and without efforts goes off. And we can behold iron magnet (photo4).

 

 

4

photo 4

 

But we have not quite enough only to behold, now let’s try to get it! Thereto we choose small drilling bit that is maximally fitted in diameter, draw attention, that drilling bit must be very close to aperture in motor’s body on the side where was stuck out the shaft. Now we lay motor’s body on the firm surface and not much rap on drilling bit like it is shown on the photo5.

 

5

photo 5

 

 

We got hold of magnet (photo 6), what next?

 

6

photo 6

 

 

Next it is necessary to take out the pasted bush, the big part of which we can’t see, emerges only its broadened component. It needs to find suitable consistent object with an aperture of such diameter that the magnet doesn’t run through it, and the bush runs. The task to tear off the glue (photo 7)

 

 

We gently strike on top, but very careful! The magnet is very fragile!

 

7

photo 7

 

The glue is torn off, there is only one little thing left. Carefully clutch the bush (don’t deform it!) and with the help of knife (hooking) detach 2 details. Photo 8

 

8

photo 8

 

Hurrah! The magnet is now our :-) Photo 9

 

 

9

photo 9

 

10

photo 10

 

11

photo 11

 

All the details are closely one to other, but it is not enough. Because even through to glue the components - all the same with the time construction will start to overtwist. And so the motor will not work. Don’t get jacked up! There is one proved way how to correct the problem. We build simple devise – «contact welding» (photo 12).

 

12

photo 12

 

We need a constant-current-source, roughly 17 volt; the resistor roughly 100-300 ohm,1-2 watt; capacitor 2200-3300 microfarad, 25 or more volt; thin multiple-core cable. We connect the capacitor to the power supply (PS) through the resistor that don’t short power supply during welding. By the experimental way we find right volume of capacitor or voltage of PS. The idea is that by the shorting the wire on the detail (boring bit) the wire is welded to the boring bit (photo 13).

 

 

13

photo 13

 

If the volume of capacitor or voltage of PS are too high then the wire instead of to «stick» just vanish into thin air and on the boring bit will be micro-crater that will reduce the fastness of future shaft. Did you adjust the device? If, Yes – then we weld the segments of wire on the shaft (photo 14).

 

14

photo 14

 

Now we can unite the shaft with the rotor and to fill a space with a special superglue between the magnet and the shaft. After the glue will have dried we shall have the firmest joining. I recommend to use the glue that doesn’t leave white incrustation. Such type of glue after drying is absolutely transparent.

 

15

photo 15

 

The rotor is ready (photo 15)

Now we start the production of bushing. I recommend to use pluoroplastic (photo 16) while it doesn’t susceptible to the temperature and has the minimum friction with metal. And also it is easy treated with office knife as it is shown on the photo 17. For this at first we bore an aperture in plate of fluoroplastic with the boring bit diameter 0,3mm. Why 0,3? Simply because of our wish for to get rid of friction (the shaft is 0,26mm). When it is necessary we file the shaft until it will be move freely in the future bush.

 

16

photo 16

 

17

photo 17

 

After this all is simple. We bring the bush to the form of pipe (photo18).

 

18

photo 18

 

The rotor and bushes are prepared! Now the worst part is the production and winding’s assembly of our micro-motor. Most likely everyone has an acquaintance metal turner. Here he is useful for us – to make a bar (future carcass for winding coil). The proportion of bar you can define yourself because the magnets are everywhere different, all the more in identical small motors from where we extract the magnets. The bar must have slightly bigger proportion then the magnet. The reserve «at length of future coil» I recommend to make rather more, after you will understand why.

An acquaintance turner made for you the necessary bar and even filed it not to speak of that he a little smoothed over the sharp corners. All this only for bottle of Coca-Cola. Your turner is not such an enthusiast? And what do you expected from Coca-Cola?  Surely you must have filed and smoothed all the corners, afterwards it will save to you time and nerves. For some reason the turners doesn’t want make the skids. The skids limit the length of coil’s winding. The turners say that they doesn’t have the necessary machine-tool…

Never mind we shall make the skids yourself using what is «under the hand». By me it was old broken DVD-ROM (photo 19).

 

19

photo 19

 

В его рёбра идеально вошёл брусок, осталось только приклеить недостающую стенку из той же пластмассы.

The bar perfectly goes into the DVD’s edges. So you must only glue the missing wall using the same plastic material. What comes out you can see below (photo 20).

 

 

20

photo 20

 

Pay attention to the surface of the skids those will touch the coil. These surfaces have convexities and return funnel and they shape the form of future winding. Such complicated form secure close abutment of two coils though the bushes those are located between the coils (photo 25).

The carcass is ready now we are winding the coils.

It is better use the thin wire, of course it is not for benefit of coefficient of efficiency, but we shall become the minimally weight of motor. To measure the diameter of wire is meaningless, because layer of isulation is different. And by the diameter 0,05mm (typical magnitude for our aims) to take off the isulation and don’t spoil the wire is very complicated.

It is better to classify the wire through the resistance per meter. I recommend to usefrom 10 to 20 ohm/m. I used the wire 17ohm/m when I was written this article.

By winding the coil to count the winds hasn’t meaning. It is enough before the winding to decide the future (necessary) resistance of winding. From my experience of produce such motors: for about gram airplane I recommend to keep the resistance in the range 28-32ohm. This makes it possible to get good enough ratio of consumption current and power of motor.

So, let’s go!

We place the skids at 0,7millimetres’ distance one from another and at a stretch we wind our 60 winds , nobody forbad to count, the length came out about 90cm. Did you wind? Now the most «pleasant»: it is necessary, keeping the coil on the carcass, to glue (saturate) it from all accessible sides with the superglue. Meanwhile don’t glue the winds to the carcass (photo 21, 22)! This operation (as majority of other) you can successful fulfil under the microscope.

Is successful? My congratulation, you on the 90% micro-aero-builder!

Now we do this operation again because we need two windings, those later we shall glue into one.

 

21

photo 21

 

22

photo 22

 

23

photo 23

 

If you still read this article so you are persistent person that by all means achieves assigned task. So, you made that what is shown on the photo 23 and you are very near from the finish.

 

24

photo 24

 

It is remained only to set the coil relative to the rotor keeping the equal clearance (photo 24). Pay attention to an axial displacement of rotor. Being in extreme position it doesn’t must touch the coil, otherwise during the work it will worn the coil.

We accurately apply the minimal amount of the glue between the bush and the winding. After we have trued and glued the second coil we will have got almost finished motor (photo 25).

 

25

photo 25

 

It is remain only to solder together every ending of every coil, so that to get one coil with two leads. These leads we must accurately solder to the microchip of Allegro firm A1442, that was special worked out for such micro-motors. The finished motor is displayed on the photo 2.

 

I am waiting for your questions on the forum. Good luck!