Arduino not powering three servos: an LDX-218, an SG-90 and a HS-755HB

Hi, I've been trying to get my Arduino to power three servos, an LDX-218 (7.4v), an SG-90, and an HS-755HB. I've tried using a 9v battery and the servos barely moved, then I tried a power bank with an output 5v at 1A, and and the LDX-218 moved, but once I connect the SG-90, the LDX-218 loses power and the SG-90 runs. From the laptop, I could power one, and I've never gotten all three to work at once. It works as soon as I use three SG-90's though, so the coding seems to be alright. From what i hear the Arduino is capable of moving far more servos then three, so i know somethings wrong. Any solutions as I'm only an amateur?

The arduino is capable of sending signals to a large number of servos.
Powering servos from the arduino is not recommended.

You might get away with powering one, small servo if it is unloaded.
But put in a larger servo, or put in multiple servos, or add a load to the servo and boom, the voltage regulator on the arduino is no longer able to meet the demand and fails.

You simply must use a separate power supply for the servos. Connect the grounds between that power supply and the arduino.

An Arduino cannot power any servos. Use a separate power supply (5 to 6V at 1 Ampere per servo) and connect all the grounds.

Would a PCA9685 Arduino shield be the solution?

That board does often solve problems with power distribution.

I just looked at your list of servos. Why are you using that particular variety of models? The HS-755HB is a 4.8-6v servo. The SG-90 is a 4.8v servo. The LDX-218 is a 6-7.4v servo.

What voltage do you intend to supply that will work with all 3 servos?

tmcg1702: Would a PCA9685 Arduino shield be the solution?

No that won't really help with this problem. You would still need to provide the power to that from somewhere, it doesn't contain its own power supply.

Steve

I'm building a robotic arm, the LDX-218 is the elbow, the SG-90 is the bicep and the HS-311 it the hand. I used these because the SG-90 and HS-311 were the only available to me, and I bought the LDX-218 as it can pivot off two points, hence it being used as the elbow

A small 9V battery is about 100 times too weak to power those servos.

Servos and motors require serious power, you cannot skimp on this. Allow 1A per servo for the small ones, and more for larger servos.

Never power any motor or servo from a logic board like the Arduino.