Need help with my first "real" project, a 12, 10, 8, 5v switch mode power supply

[atsch]

I've been working on a robotics project for a while, and I've come across some power problems. I need a *ton* of different voltages, and my original linear regulator design is really inefficient.

Here's what I need:

• 12 at 6-8 Amps (4 12v motors taking 2 Amps at max speed each)
• 10v for an (up to) 10 Watt LED (don't ask)
• 8v for motor controller and arduino (arduino has a built-in regulator)
• 5v to decrease load on the arduino's built-in regulator for high-power Ultrasonic and infrared sensors

Here's how I've been doing it:

• 3 * 7812 (2 amps) in parallel (big regulators are terribly expensive)
• resistor takes power from 12v regulators for LED (it dims when the motors start moving because the motors spike in power draw)
• 3 amp 7808 for motor controller and arduino
• arduino internal 5v regulator

BTW, this whole thing is powered by two 20c 7.4v Li-Po batteries in serial, nearing 12v when empty

as you can see, this is supremely suboptimal, and I need a replacement, however my electronics experience is practically nonexistent, I've only used development boards and made some simple sensors (e.g. high power reflected light sensor), so I need your help.

My fist thought was building a switch mode power supply for my 12v needs, and powering the rest via linear regulator. However there is a bunch of problems: I can't put anything behind the 12v regulators because the initial power draw from the motors is insane (Would a beefy capacitor help?), and I'm sure 78XXs don't appreciate PWM flicker that much.
So instead of putting the 8v stuff behind the 12v regulators, I have to put them in parallel, which brings me back to my problem of wasting a bunch of energy (12W according to my calculations).

What is an good solution to this problem? Every solution I come up with just ends up being a bad Idea in some way, and I'm sure there's a common way to deal with this.

[tggzzz]

Why do you have to use linear regulators?

There are many ready-made switched-mode DC-DC converters which won't "waste" power.

[atsch]

I have yet to find a ready-made switch mode power supply that can can supply 12v at 6-8 amps. I could of course use premade PSUs for the other voltages, but with space at a premium I feel like it is much more sensible to make my own power supply.

[Riotpack]

What about something like this http://www.airyear.com/ltc3780-automatic-buckboost-module-red-8a-p-110345.html?zenid=41cf1acafcb591bc79d1988ff1493f26

I would soft start motors running from a SMPS, especially if more than one is starting at the same time.

It's a buck-boost, so it doesn't need the ~2v overhead of a standard linear reg.

[Riotpack]

If you want to design your own take a look here -

http://www.ti.com/ww/en/simple_switcher/design-tools.html

You may have to go for a buck/boost design due to your Vin equalling or very close to your Vout when the battery is at its low point.