Powering Multiple Servo's

Hi, I'm currently working on making an animatronic hand that when I bend a flex sensor, a servo pulls a string which pulls a finger.

I was able to get one finger to work flawlessly, however, when I insert another servo, it loses power. I am currently using MG995 Servos. The way that the original servo was getting power was through a wall adapter (120V ---> 7V) which I cut the end off to form positive/negative leads. When I tried hooking up the 2nd servo to the same power supply, they both performed much worse.

Why does this happen and what can I do to power multiple servos without the performance going down?

This question comes up a lot.

I looked at the first page of thread titles and found these two threads which provide some information on the topic of powering servos.

http://forum.arduino.cc/index.php?topic=364189.0

http://forum.arduino.cc/index.php?topic=365811.0

There are likely other threads with additional information.

Powering multiple servos is harder than most people think.

Not all servo can safely use 7V supplies.

I guess the thing that I am confused about is what is there a deficiency of. Volts? Amps? Watts? What do I need to increase and what do I insert into the circuit to make it happen? Here is a quick picture I made of what my current circuit looks like without the flex sensor.

http://devinsikes.blogspot.com/

Amps. Need a beefier power supply - one that can supply more current.

I switched the wall outlet which outputs 100mA with 4AA batteries and they all seem to work. Is this okay? Is there any risks in hurting my servos by using this?

4AA can output ~2500mA, much better solution than a 100mA wallwart.

drsdrs: I switched the wall outlet which outputs 100mA with 4AA batteries and they all seem to work. Is this okay? Is there any risks in hurting my servos by using this?

No you won't hurt your servos with four AA alkaline or NiMH (or NiCd). There are AA Li-Ion batteries. Four of these could fry a servo.

It's very common to power servos with five NiMH cells.

A good rule of thumb is to budget 1 ampere per servo. Fresh alkaline AA batteries can supply only about 2 amps, for a short while.

NiMH battery packs are much better. For several servos, I suggest an RC car battery pack like this one.