UNIT 14

UNIT 14

Lesson 14 40 mins

PROPELLERS (5 mins) 

Propellers are the ‘fans’ mounted on the motors. As the motors rotate, the propellers also rotate and these rotating propellers generate thrust. Hence, propellers are an important factor in the study of drones. The topic is aimed at teaching the students how thrust is generated using propellers and knowing about clockwise and counterclockwise propellers.

The spinning propellers on motors generate thrust. The design of the propeller is significant in this thrust generation. The cross section of a propeller is an aerofoil whose aerodynamic shape helps in generating thrust. 

Refer: How do Wings generate LIFT 

SQUASH RACKET EXPERIMENT (10 mins) 

This experiment shows how air is thrown downwards by a propeller or a blade.

Swing a squash racket over a few pieces of paper. First, swing it with 0 angle of inclination with the horizontal. In this, the pieces of paper should not move as the air will not be thrown downwards. Next, swing it with some angle of inclination with the horizontal. When doing this, air will be thrown downwards and pieces of paper will move. This experiment will help in understanding how air can be thrown downwards, and thus generate thrust using a propeller. 

PARAMETERS OF PROPELLERS (10 mins) 

These are few basic terms associated with propellers which can be easily taught to students.

Diameter of a propeller: ​The end to end distance of the propeller is called the diameter of the propeller. 

Pitch: ​Propeller pitch is a linear dimension usually expressed in inches, feet, millimetres, or meters, and is equal to the advance of the propeller in one revolution.

CONFIGURATION OF PROPELLERS ON DRONES (5 mins) 

It is an important topic as the drone would not fly if the propeller configuration is wrong. Hence, make sure that the students understand the propeller configuration properly. Also, this topic teaches the reason behind the propeller configuration which is fairly important concept to understand for the students.

Diagonally opposite propellers should have the same rotation and neighbouring propellers should have opposite rotation. Why? 

When we have a propeller rotating in a certain direction, consider a clockwise rotating propeller (A)​, it generates a torque on the body in the counterclockwise direction. This causes the entire frame to rotate in the counterclockwise direction,so to balance this we need a propeller that generates a counterclockwise (B) torque to equalize torque on the frame. 

Thus a clockwise propeller must have a counterclockwise rotating propeller adjacent to it. 

Now in a quadcopter we have placed 2 (A&B) propellers with opposite rotations so we have to do the same with the remaining 2 propellers. So the propeller with counterclockwise rotation (B) must have a clockwise propeller (A) adjacent to it for the same reason that we need to balance the forces on the quadcopter. And then this clockwise propeller (A) will need another counterpart to keep things in balance thus another counterclockwise propeller (B) in adjacence. 

So if we finally see the configuration, we have diagonally opposite propellers to be of the same rotation. 

REACTIVE DRONE EXPERIMENT (PLUTO BLOCKS) (15 mins) 

This experiment will show the effect of using only CW or CCW propellers. It can be demonstrated by the trainer to explain the above topic hand in hand.

Program the drone such that only clockwise or counterclockwise motors will work at a time. This will make the drone go in counterclockwise or clockwise direction respectively, because of the reactive torque. 

Use throttle mode for giving input to motors as it will enable to observe a gradual increase in rpm.

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