I'm not sure where to start so if this gets a bit off track please forgive me.
Alan Hann has built and test flown a half A model for electric using fairly inexpensive  motor is my understanding.
I'm wondering first how hard and how long assembly of the motors were and took?
I also wondered at the different choices of wire size and number of wraps why he choose say 26 wraps vs 27 ?
Was there a reason to add just 2 wraps more or not just 1 more ?
My last question is how do you know how many amps are  used or left in the battery pack?
I think I understand what all I need to build and try electric cl flight but before I do try I'd like to be able to make sure I have a good understanding of it and be able to do bench tests first.
Please excuse any errors I've made in spelling.
Jim Gilmore

Jim,
Let me explain where I was coming from in my choices. I should say right off the bat that they are not unique, nor they are not the cheapest, but they were fun for me.

As I mentioned on one of the threads, I wanted to fly an electric 1/2A in a local 1/2A contest. The CD said fine, as long as I didn't use a prop with a diameter greater than 6 inches, nominally the largest prop that you would see on an 0.049 engine (like a Cox Black Widow). I had a Brodak Arf Baby Clown that I flew last year in the contest with a Blackwidow, so I thought that would be a good plane to use as a test bed. When I took off the BlackWidow and weighed it, it came to 2.1oz with prop, but no fuel, so I thought that would be a good target to shoot for. Also a BlackWidow can swing a 6-3 like prop in the 14-14krpm range (on the ground) with pretty good performance, so that again was a preliminary target. It is often said that a 0.049 puts out about 50 watts of power, so I grabbed that number too (I think it is a little low for a modern 1/2A though). Finally this contest has everyone fly the beginner pattern, so you are talking about a flight which last less than 3 minutes (actually ~2 minutes as it turned out), so that Plus the 50 watts said I needed a powerplant and power supply which could supply that power for ~3 minutes.

So in choosing where to start, I decided to go for lipo battery--the lightest for the contained energy (+I already had the charger). Lipo's come in fixed voltages of ~3.7V per cell under load. So a 2 cell lipo with the cells in series (=2s) would give 7.4 V, and a 3 cell lipo (3s) would give 10.1V. Since power in watts =Volts*Amps, and I wanted nominally 50 watts, the 2s battery would need to supply about 7 amps continuous, and the 3s a little less than 5 amps. Here's where I made an arbitrary decision. I was thinking that maybe I could imagine making a beginner type setup---and here beginners might not want to use a lipo, but maybe a Nickel-Metal-Hydride (NiMH) battery. Well a typical NiMH pack has ~6 cells for a voltage of 7.2 volts, close to the 2s Lipo voltage, so therefore I decided to build a system that would make about 50 watts off a 2s lipo battery that could spin a 6 inch diameter prop in the 14krpm range, and would weigh close to the 2.1 oz of the original Black Widow. I could easily have gone for a 3s system, and then I would have chosen a different wire wind on the motor, and a different capacity lipo. I will say up front, that to first order, you could have chosen either path and come up with the same performance and about the same weight. The only proviso is that battery sizes (and weights) are not infinitely variable, so you are stuck with what is in the market place.

Since I wanted to wind a motor as for my larger planes, I thought it might be better/easier to start with a smaller motor with thinner wire (easier to tightly wind). I did some research and came up with the Gobrushless GBx1 kit which is based on a 22mm diameter stator from the motor of a CD-ROM drive (like the one in your computer). Here is the link http://www.gobrushless.com/shop/index.php?app=ccp0&ns=prodshow&ref=GBx1
The weight of this motor is in the ballpark and it can handle the power I wanted (according to their specs)

Since I wanted to spin the prop in the 12-14krpm range using a 7.4V battery, I needed a "kV" such that 80% of kV*7.4V~12-14krpm, or kV should be about 2400 rpm/Volt. The Gobrushless site has a database of motors that people have already wound, so I checked that out to see what looked like it was in the ballpark. Since I was winding, if it was off, I could always rewind. Anyway that's where I came up with the 11 turns of 22 gauge wire. Realize that you need to have the correct gauge wire available, and I did. Anyway I just could get 11 turns per tooth--not much more space left. If I only put 10 turns, then my kV would be higher, but your motor efficiency depends on how much copper you can cram in. I don't think I could get 10 turns of 21 gauge wire to fit for example. Anyway you stick as much as you can, and if the kV is too low (since I was stuck with a 6 inch prop---but I can play games!), I could always rewind one turn less. As it turns out, this actually worked for this motor.

Finally I had to choose the actual battery. This is always the scary part. Because they aren't cheap and they aren't returnable. I had a 2s battery hanging around from a previous experiment that didn't go the right way, so I was able to use it to test run the motor on the bench to get a few data points before I chose the real battery. (This test battery was a 2500mAHr cell, and so was way to big and heavy for a 1/2A plane, but it was ok for the test). Anyway I saw that I was indeed pulling about 10A on a 5.5x4.5prop (13krpm) statically, so I thought things would unload in the air (and the current would drop. Anyway 10A for 3 minutes is like a 500mAHr battery (sucked dry), so I thought a battery in the 700 range would be ok. So to make this long story come to an end, the best battery out there for the weight was a ThunderPower ProLite 2s 730mAHr pack which weighed only 1.1oz. So I ordered one (~$30). In the end it worked out just fine for me.

So there you can see some of the choices I made. Like I said, I could have wound the motor for a a 3s 500mAHr pack (about the same energy as a 2s730 mAHr pack) (kV to shoot for would be 2/3 of 2400 rpm/volt  (or 1600rpm/volt) and I would have a equivalent setup. I would need about 3/2 the number of winds (or about 16-17 /tooth) with thinner wire of course to fit. But the performance should be identical, assuming I could find a 3s 500 mAHr pack that weighed about the same (not always trivial).

And if you have seen some of my photos, I have tried stacking two 6-4 APC E props on top of each other and that works well, but also a 6-5.5 APC E prop is my current choice.

Whew!

Hi Jim,
You'll have to spend a bit more than $60 for a charger that gives you any useful information. You should buy a balancing charger, both for safety's sake and for better battery life. As you said, you want one that either displays the capacity put back in, or the capacity left at the start of the charge. I like the FMA line of CellPro chargers myself. There are sevaral balancing chargers now showing upo on the market from far East houses. I'll bet we have several threads devoted to chargers.
and we're off!
Dean