Hello. I am currently working on a simple robot project that uses a servomotor, a DC geared motor and a weird IR reciever.
The thing is near completion, but I still have one big worry on the electronic side: I would like to make the thing run on its own, without any cable. I currently have a 9V battery feeding my DC through an H-bridge, and I would like to know if it was safe to also run the battery in the arduino's Vin. (While I did hear that 9V batteries are short-lived, I will not take another one: this project is mostly experimental, I want to see it roll)
Also, the servo is currently powered through the arduino's 5V: is it that bad?
I think you mean a hobby servo, not a servomotor!!
Yes a small 9V battery is inadequate for motors/servos.
Yes powering a hobby servo through the Arduino 5V logic rail is bad.
Something like a 6V RC servo battery pack would be good for powering the servo and the DC motor.
What voltage is your DC motor? What motor driver/shield do you have? What current does the motor
use? What is this "weird IR reciever"? Details details details, everything is in the details.