I am putting a Vector through its initial flights right now. I am using a Scorpion 3020-xx motor, and so an AXI 2820-xx would work ok---pr almost any equivalent outrunner motor with similar internal guts.

The question of the "xx"  (the "kV") is for the following reasons:

I expect the Vector to take more power than my Nobler, simply because its airfoil is thicker, and I may also fly on longer lines (=more flying time so more energy is needed). I don't want to buy the battery right yet because I am not sure how much I really need. So for now I am using two 3s2100mAHr packs, hooked up in parallel, making a 3s4200mAHr equivalent energy source. I really expect this to be more than enough. As soon as I know what "enough" is, I'll try to size the battery.

Now since I am using a 3s pack, the nominal voltage the pack provides is ~10.5V under load. To get the rpm I want, I am using a 3020-12 motor--with a kV of ~1100 rpm/volt. RIght now a 12-6 prop at ~8500 rpm is feeling pretty good, but that was only one flight so far of 2 minutes.

I am guessing that a 4s2100mAHr pack is too small (four 2100 mAHr cells) since it just makes it with my smaller Nobler. If I stick with 2100 cells, I could add a 2s pack in series to make a 5s2100mAHr pack, but that would want a motor in the kV=3/5*1100 rpm/V range or ~660rpm/V. The nearest I have to that is a 3020-730 motor, which would probably work ok.

So what is important to you is you need some pack equivalent (at a minimum) to 5x2100---or ~10500. If you want a 3s, then each cell needs to be 3500mAHr (10500/3). If you want a 4s setup, then each cell should be 2600mAhr or so. Etc etc. (I am guessing Dennis A.'s 4s2500 mAHr packs are darn near perfect---too bad they don't seem to be available any more (AFAIK).

I would also check the sticky list above, since one of the electrified Adamisin's clan has already run an electrified Vector.

I will note that my stock Brodak 3s4000mAHr pack just barely fits into the Vector fuel tank area---and the balance looks pretty good.

With my 2x 3s2100 pack trial setup, my eVector weighs in at 48oz, so I would like to shed a little weight. But that is how I also began my Nobler 1&1/2 years ago. When I saw I was barely using 1/2 the total capacity, I decided a 4s2100 pack would work too (at a ~2.5oz weight savings).

It is always safer to oversize the battery, (as long as it fits), rather than undersize. I recommend going easy on the first battery purchase until you see what works, then buy exactly the pack(s) that you need.

so on the ESC - does it matter which on it is....I see 3 different Castle Creations 45A ESCs listed

also - the battery jargon - I dont understand....

I can get the Scorpion motors over here in NZ - but the listed names are different - there are 3020-890 - is the last number the volts?

so on the ESC - does it matter which on it is....I see 3 different Castle Creations 45A ESCs listed

also - the battery jargon - I dont understand....

I can get the Scorpion motors over here in NZ - but the listed names are different - there are 3020-890 - is the last number the volts?

About the Castle ESC - you need the Phoenix 35 for the 4-cell (4S battery) or Phoenix 45 for the 3-cell (per Alan's guidelines above) you do  NOT need the "HV" model of the ESC.

The Vector will fly with a 10" prop, will fly better with an 11" prop and probably better still with the 12".

Back to the battery, we have had some success with three cell batteries, but have now standardized on 4-cell.  You will need a 2500 mah pack at a minimum, but 3000mah is a little overkill.  The advantages of the smaller battery are lighter weight (up to 2.5 oz lighter) and (probably) lower costs.

One more note on batteries.  As you go looking at them you will probably see them showing a "C" rating, like 20C, 25C, etc.  Higher ratings mean the battery can "give up" energy faster - but anything higher than 20C is not needed, but higher C ratings usually mean the packs are more expensive and heavier.

Hope I have not scared you away yet!

Last thing for now: some motors can only be mounted from the front, some only from the rear, and most - including the Scorpions - can be mounted either way.  We mounted the Brodak motor in the Vector ARF from the front because it is the only way that motor is designed to  be mounted.  Its a tight fit but can be done.  Frankly, rear mount is usually easier to do, and gives you a little more room for cooling ducting.  Unfortunately, we are all still new enough to this that no one can say with complete accuracy that either front or rear mount is clearly better - each has their advantages.


and a LAST last thing.  As Alan mentioned the Brodak battery we used in our conversion was a tight fit - if laid flat.  I chose to install it on edge - this also let air get all around it.  Here's a couple pix...


 

Lithium Polymer batterys have a nominal voltage of 3.7V per cell and peak charge to 4.2 volts thus:

Cell count     Nominal V    Peak V
1S (1 cell)        3.7V         4.2V
2S (2 cells)       7.4V         8.4V
3S (3 cells)      11.1V       12.6V
4S (4 cells)      14.8V       16.8V
5S (4 cells)      18.5V       21.0V

and so on.  So if you are seeing packs listed with other voltages then most likely they are not Li-Po batterys
 

What Alan meant to say is that you put 1 volt you'll get 890 rpm.  10 volts you would get 8900 rpm.