Hi,
I am using an UNO and 6 MG996r servo motors to make 6 DOF robot, but as I was diving deeper into the project I realized 4AA batteries linked in series outputting only 6 volt with maybe 2-3 amp hours is not enough for my project...
So, I have been reading a lot about the powering issue.
If I want to power it with batteries, I need at least 6v 18 amp hours(please correct me if I'm wrong). And basically I read that the 4AA battery pack in series will power one servo... So to power all 6 of them, I need basically 24 AA batteries, which I think is not that good idea... So, I looked into other batteries, but of course all of them had their own pros and cons... so I need some help how to power my 6 servos. I would be glad to hear any help on this lost soul xD.
But if I want to power it via wall outlet, I thought I need an adopter that outputs 6v with around 5A would be sufficient... please correct me. So what I am saying here is also, I need help 
Do you think I should power it by batteries or through the wall outlet? And for either of them, how should I achieve the needed voltage and Amp or amp hours?
In advance, thank you very much!
You are misusing, misunderstanding amp hours. It tells nothing about the current that can be delivered.
If You draw 1 amp that 18 amp hour batterie would work for 18 hours. The opposite, 18 amp during 1 hour is likely no true.
The way to calculate your power requirements is to focus on the current draw. If each of your servos can draw 2-3 A, then you need 24 A total power supply capability.
Next, you need to know what voltage is suitable for your chosen servos. Often, these servos can run on 7.2V (i.e. 2 cell LiPo pack).
So, your best bet would be to get a 2S LiPo that can supply 24 A. LiPos are often listed with their current supply capability in terms of C (amp-hours). A 5C 3000 mAh pack can supply 3*5 = 15 A of current.
OH, that's right. Wait, then, if my servos need around 15 amps my 4 AA battery pack would be enough to draw current but it would just drain the battery faster right?
I found a 7.4V 2700mAh battery with 20 c rating (2s). Just to be safe if I use a voltage regulator to drop the voltage to 6 volts do you think this is good enough?
The MG996R briefly draws the stall current (2.5 Amperes) every time it starts moving. So, your power supply needs to be capable of providing 6 times that or more, at least 15 Amperes.
Otherwise you will just have a twitching mess of servos, which can be pretty funny.
So, with a 7.4V 2700mAh battery with 20C rating(2 cells) do you think it would work? And I want to be safe so, if I use voltage regulator to drop the voltage to 6v, would the current be enough?
That should work as it is 2.7 x 20 = 54A max.
Two concerns:
- The battery makers often inflate the C ratings, and I would not trust such a high number. But even at 5C rating, you'll likely be OK
- Please check to see if the servos can run off 2 S LiPos directly. Likely they can, but double check. Because if you use a voltage regulator, you are back to running into current supply issues. Most wont supply 25+ A
Yes, if the voltage regulator can easily handle 15 Amperes. Look for one rated for 20-25 A.
A better choice is a 6V NiMH battery pack. RC hobby suppliers have them.
Among 6v nimh batteries do you recommend any specific ratings or models? when I look up 6v NiMH batteries, I see one with 2700mAh. Do you think this is good enough?
If the battery rating is 10C or higher, yes.
Oh, that's weird. Most of the batteries I looked for they didn't mention any C ratings... is there a way to manually calculate the C rating?
The RC hobby shops usually state the manufacturer's C ratings for battery packs, or the maximum continuous discharge rate in Amperes (significantly lower than the peak discharge rate).
I see. Could you find a link for one please? Because I have been looking for hours for the ones that have C ratings with 6 volt NiMH batteries, but I was unable to find one... it will be so helpful...
Oh, I see. Thank you! For this one the 10A is kind of equivalent as 10C?
BTW do you know any other brands or models that are similar to this? Because I am living outside of US and to ship this cost way too much, so hopefully I can find one like this model where I can locally get it or order it with less shipping fee. I know I am asking a lot... Thank you so much for your help!
It would be best to do your own purchase research.
Yes, thank you very much for all the help! Sorry 
I asked you so many questions. Thank you!