A quadcopter, also called a quadrotor helicopter, it is a multicopter that is lifted and propelled by four rotors. Quadcopters are classified as rotorcraft, as opposed to fixed-wing aircraft, because their lift is generated by a set of revolving narrow-chord airfoils. Walkera QR Infra X is such a toy.
Unlike most helicopters, quadcopters use 2 sets of identical fixed pitched propellers, 2 clockwise and 2 counter-clockwise. These use variation of RPM to control lift. Control of vehicle motion is achieved by altering the rotation rate of one or more rotor discs, thereby changing its torque load and thrust characteristics.
The Walkera QR Infra X RC quadcopters use an electronic control system and electronic sensors to stabilize the aircraft. With their small size and agile maneuverability, these quadcopters can be flown indoors as well as outdoors.
There are several advantages to quadcopter over comparably-scaled helicopters.
First, quadcopters do not require mechanical linkages to very the rotor blade pitch angle as they spin. This simplifies the design and maintenance of the vehicle. Second, the use of four rotors allows each individual rotor to have a smaller diameter than the equivalent helicopter rotor, allowing them to possess less kinetic energy during flight. This reduces the damage caused should the rotors hit anything. For small-scale UAVs, this makes the vehicles safer for close interaction. Some small-scale quadcopters have frames that enclose the rotors, permitting flights through more challenging environments, with lower risk of damaging the vehicle or its surroundings.
As the time went by, RC toys are become more commonly popular in the market today. The four-rotor design allows quadcopters to be relatively simple in design yet highly reliable and maneuverable. So, I think the Walkera QR Infra X RC quadcopter is really good for you, just belive me, you can get a lot of fun from it.