FAA Regulation

Remote Pilot in Command (Remote PIC). Person manipulating the controls. Visual observer.

No more than three as long as the Remote PIC maintains visual line of sight. As many as he/she can handle. No more than one. 

If prior permission is received from the Federal Aviation Administration. If precautions are taken to avoid injury or damage to persons or property on the surface.  Only in an emergency.

Quadcopter capturing aerial imagery for crop monitoring. UAS used for motion picture filming. Model aircraft for hobby use. 

must not cause injury equivalent to 25 foot-pounds of kinetic energy upon impact. be operated in accordance with the operating limitations specified in the approved Flight Manual. be 0.55 pounds or ...

does not contain any exposed rotating parts that would lacerate human skins upon impact. has an airworthiness certificate issued under Part 21.  is labeled as Category 4.

Only when visual observers participate in the operation. Alone, if operating during daylight hours. Under the direct supervision of a Remote PIC.  

Ensure the aircraft is equipped with a parachute. Ensure that the area is restricted-access and that everyone inside moving vehicles inside the area are on notice.   Ensure that everyone inside ...