Wireless Power / Charging Design Help

Hopefully a few of you out there have some experience with wireless power and can help me get started with this.

As part of my Robot rebuild I will like to try my hand at wireless power/charging. I have used a charging dock in the past and while it works wireless power would be cool and I won’t have to worry about direct contact and polarity. http://mobilewill.blogspot.com has my projects with pictures of my charging dock. I haven’t posted pictures of what my new robot will look like yet. But it is based on this http://www.sparkfun.com/products/10336

I found a few how to’s to get me started a still a bit confused.

Here is one of the ones I found that seemed to get good current draw.

My goals:
2-3 inch distance
as close as possible to 2A (I know that is probably pushing it)
<=12v on the remote side

I will be charging 2 batteries that are on-board and have their own charging IC. Just need a power source.

So my question is how do I figure out turns/size for the required current? Is the example above a good way to get AC power?

I did some searching and not understanding the DC-AC conversion and turns/size.

Also some examples like above don’t use magnet wire, but regular wire. So what wire and what size?

I know its a lot of questions, but maybe someone can offer a enough for my brain to put it all together?

Note: Unfortunately I don’t have a oscilloscope. Its on my list of stuff to get one day.

Thanks for the help.

I've never done anything like that so I'm no expert...

I doubt you are going to get anything more than a trickle at 2-inches. You are essentially making a transformer, and transformers work best when both coils share the same iron (or ferrite) core.

2-Amps is probably possible... I think some fill size electric cars use non-contact charging. But, the thing would probably be so heavy & bulky that your robot won't move.

So my question is how do I figure out turns/size for the required current? Is the example above a good way to get AC power?

More turns gives you more inductance and more resistance. I think you generally want high inductive reactance, but low resistance. Low resistance will give you high-current when you need it, and high inductive reactance will prevent excess current/heat in the primary with no load.

Also some examples like above don't use magnet wire, but regular wire. So what wire and what size?

Magnet wire allows more wire/turns in a smaller space because the insulation is less bulky. Otherwise, it's just regular 'ol solid wire.

I did some searching and not understanding the DC-AC conversion

AC-to-DC just requires a rectifier (usually a full-wave rectifier) and a capacitor if you want to smooth-out the DC. DC-To-AC requires an oscillator. A higher-frequency oscillator allows you to use smaller transformers than with 50/60Hz line frequency. (I think it's the higher inductive reactance you get at higher frequencies.)

...turns/size.

The primary/secondary turns ratio gives you the primary/secondary voltage ratio. Of course, this assumes good magnetic interaction between the coils, which you won't get with a 2-inch gap. And, you need enough turns for inductive reactance. i.e. With a couple of turns on both sides, you are going to draw too much current and fry something on the primary side. This is probably one of the reasons (besides the air-gap) why the iPod charger is so inefficient, drawing 3 Amps from the primary while delivering a few milliamps to charge the ipod.