How much volts ?

Projects General Guidance
1

Hello,
I am kinda new to arduino(uno)
I want to make a obstacle avoiding robot which would consists of:

  1. 2X plastic gear motors
  2. 1 sharp IR sensor or SRF05
  3. 1 mini servo
    My question is that if i use 9v external power supply for above electronics will it harm any of them ?
2

If you use regulators capable of handling the required power, no, you won't cause any damage

http://www.skpang.co.uk/catalog/product_info.php?products_id=401
See the bit about supply voltage.