I am working on this project to detect anything that is entering the zone of RC helicopter blades (around 10cm diameter) region and stop the rotor. It needs to detect any solid object so metal or plastic or human body.
I was thinking to use ultrasonic sensor such as HC-SR04 placing on top and bottom of the rotor in such an angle that it just scans the region right outside blades (because I don't want the spinning blades to cause any feedback). But since it only has 30 degree angle of accuracy and I need a full 360 degree sweep (because object could approach in any direction), it means I would need more than 8 of them, which is too many. Then I was thinking to let 3 or 4 of them spin at top along with the rotor shaft in a slower rpm. But I am afraid that since it's not guaranteed the same receiver gets from his pair transmitter, the time will be mixed up, which might cause Arduino to think something is close when it's actually far away.
I was also thinking of using maybe infrared sensor such as SHARP 2Y0A21, and place them on top and bottom, but it also needs many of them to cover the 360 degree which is not ideal.
Therefore I am really confused at what is the best approach and what sensor/implementation should I apply? I realise my wording is hard to understand, so please don't hesitate to ask me any question.
PS: at this moment can assume the RC helicopter position is fixed and only consider the rotor system (blade, motor, sensor system). And the system should detect object in advance so the blades can slow down. for example if it's hand approaching, the blades should not injure the hand.