Friday, April 10, 2009

Construct your own motor!

Good day everyone. This will be my debut post for this blog.

There is one very important rule when you want to start building something with engineering sense- the parts needed for you to assemble the prototype is AROUND you; you just need to realize that it is already there. (a modified quote from McGyver)

For my part, I started with gathering some parts which can be scavenged; plastic bottle tops for the winding frame, insulated wire from transformers (from broken electrical appliances-don't buy any insulated wire PLEASE. They're everywhere, from broken TVs, large inductors, etc. When you start to dissect your own scraps, you'll understand.), gears from broken mechanical clocks are excellent for mechanical reasons, you'll see, shafts can be obtained from broken toys and pens for extra structural reasons. From all these, you will spend virtually zero for this project, apart from some glue for good measure. Anyway, this is the challenge from us of VORTEX ELECTRICA: How cheap is your prototype? 'Coz the cheapest WINS.

We'll start on the armature. There are two configurations which I considered; the first one will be an alternate two pole armature shown below:

The coil winding is perpendicular to its commutator contacts, which I constructed using a tubular radio antenna, which I halved using pliers (this is a bit tricky, you can flatten the antenna and deflate it until it breaks apart using pliers, you should get it halved nicely). Personally I think the contacts works best using radio antennas; most project from the 'net uses aluminum wraps or from cans, they tend to oxidize and leave an insulation on the surface after some time.
The halved antennas are glued onto a cylindrical plastic spacer, from pens. REMEMBER: THE INSULATION ON THE TIPS OF THE WIRE NEED TO BE SCRAPED.

I used a second, more powerful armature design, using transformer cores shaped like in the picture below:

You can see that the transformer cores are drilled so that it can be mounted to the shaft. Now, drilling is a very important process in construction of prototypes; make sure you have a cordless drill-it should cost around 70-150 bucks depending on quality.
The important part is: how do we orientate the coils? This is difficult to explain, but imagine three solenoids oriented likewise, and the contacts are 'commoned' identically with respect to each other. Of course, you must solder these joints, and for soldering, I assume you had the basics. See diagram below:

This should give you some idea. And oh, the three contact plates/commutators should be placed so that between two solenoids, one plate of the commutator is placed coaxially in between. Then, solder the 'commoned' windings onto the plate. Use some soldering paste to aid this. So that should do it. Three common terminals soldered on three plates.

Either way, you can use one of these configurations for starters.

Now, the rotor should be mounted using metal frames or anything on a magnet, in my case I used a speaker magnet from a broken radio (also an excellent source for scavenging) and test the armature's functionality using stripped wires connected to batteries (3-9 volts is enough). Just touch the contacts and you should at least see some jerks from the armature.

By principle, once power is supplied to the armature, only two solenoids is electromagnetized. This process happen repeatedly for each of the respective solenoids, sequentially. The orientation of a 3-pole provides sort of a way to counter neutral points, where the motor always will need a startup torque using external force; this happens sometimes if the number of poles are even, but for odd number of poles, InsyaAllah it will never happen. So, to put simply, the motor will forcefully turn upon the orientation of the poles.

If it doesn't move, check for short circuits and other stuff and try again until it's done.

From here, everything else is easy. I used plastic plates from scraps and used to construct the body. See below:

Next, the construction of the permanent brushes should be done. I encountered using strips of aluminum from cans for brushes, but the oxidation on aluminum, even after sandpapering, is quite inevitable. So I opted using wires instead. But there is a problem; wires aren't springy, which means after a while the wires will not be in contact anymore with the commutators. So what I did is to straddle the stripped wires with springs from mechanical pens, and they did an excellent job.

Here's the diagram:

I finalized the motor with extra touches of mechanics for the batteries and so on:

Notice that I added another magnet to homogenize the permanent magnetic field, and a metal turbine to indicate rotation.

This motor turns quite fast for 6 volts (4 AA batteries). Screws are always needed to assemble the plates; this makes drilling even more imperative.
Try it! It's very interesting to see something that moves from your works!
Have a nice day.
May Allah bless all of you. See ya!
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