New to ROS - Want to get quadrocoptor or drones

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That question depends on what kind of budget you have but it's likely a higher level project. The cheapest quadrotor on the market at the moment is the AR Drone. While a lot of fun to fly they are limited and may or may not be applicable to your project. You can build something considerably more capable for about $600. I've done this by combining a Guai 330X chassis (which is no longer for sale) and an ArduPilot Mega. Beware that this route requires a sizable time investment to achieve programmatic control over such a device. If you are not tied to the idea of using real robots you could consider the hector_quadrotor statck. IIRC it is a quadrotor simulator built on Gazebo and should allow you to work with a swarm.