Serial Help

So I have been working on a project that requires both an Arduino and a Raspberry Pi. Arduino for real-time adjustments, Raspberry Pi for video streaming and connecting to a server were it will get commands. My issue has been trying to have the Raspberry Pi communicate to the Arduino over Serial. In a perfect world I would have used USB to USB and it would have worked but my Raspberry Pi wont recognize it unless it is on a powered USB hub so I am beginning to think power is my issue. I attached a rough diagram to the post. It goes Battery(11.1v) → Arduino & 5 Volt Regulator. The Regulator feeds power to the raspberry pi. Then a USB cable goes between the Arduino and raspberry pi. This only works if I use a powered USB hub. Why? is their something wrong with my grounding.

Circuit Diagram.pdf (13.1 KB)

Don't think it's a GND connection. Then the USB cable itself would fix it. But what is powered by the Arduino? The Arduino can hardly deliver any power when powered from 12V. Why not just power the Arduino from the 5V as well?

I tried that and it didn’t work so I assumed that arduino wasn’t getting enough power. The arduino is connected to a mpu6050 sensor and 4 esc’s

No idea what are those. Found the mpu6050 as being a Accelerometer + Gyro. But ESC?

You didn't specify what kind of Arduino so I assume a Uno. And a Uno works on 5V. But you can't feed that from the Vin or the barrel jack. Only to the USB port or the 5V pin.

They're Electronic Speed Controllers they're used to drive motors. They connect to the arduino and receive a PWM signal which tells them how fast to spin the motor.

These are the ones I have

Don't think they need much but okay.

To easy feed the Arduino, just splice a USB cable and directly connect the power lines to the Arduino to the same 5V supply of the Raspberry. What is the rating of the regulator?

The regulator is rated for 5.3 volts and 3 amps. I will try that thanks!