Quadcopter Dynamics, Stability and Control

A brief introduction to quadcopter (drone) working. It provides an overview of flight stability, dynamics, general control system block diagram, and the electronic hardware.

1. QUADCOPTERS
DYNAMICS, STABILITY AND CONTROL
Blesson Easo Varghese
Control Systems Engineer

2. Fixed wing aircrafts Rotorcrafts
▪Engine is used for only forward thrust
▪Lift is produced by fixed wing
▪Control surfaces are used to change orientation
▪More stable comparatively
▪Less manoeuvrability
▪Engine provides lift as well as forward thrust
▪Lift is produced by rotating wing
▪Manoeuvring is done by changing rotor
parameters
▪Generally less stable
▪Complex rotor mechanism

3. Reaction torque in rotor system
▪All rotor system suffer from reaction
torque as per Newton’s Third Law.
▪This torque tends to rotate the entire
body in the opposite direction of
rotor motion.
▪Helicopters arrest this reaction
torque using a separate tail rotor as
shown.
▪Multicopters avoid this phenomena
by having their rotors rotating in
opposite directions.
Gyroscopic
Precession

4. Multicopters
▪Widely used as drones, as all the manoeuvres can
be performed just by varying the rotor speeds.
▪Control surfaces are absent
▪Mechanically simple, but electronically complex
▪Efficient control algorithms are required to
achieve stability
Quadcopter
Hexacopter

5. Degrees of freedom
pitch
pitch
roll
yaw
Six degrees of freedom
▪Three translational motion
(+)
▪Three rotational motion
NOTE : All degrees of freedom are achieved by varying only
a single parameter – the speed of the rotor.
Total number of possible independent movements.

6. Static Stability
▪Whether the aircraft is able to regain its original state after the removal of a disturbing force ?
(Positive stability) (Neutral stability)

7. Stability of Quadcopter (Neutral)
1
2 3
4
Total lift
Vertical stability Horizontal stability

8. Dynamics of a Quadcopter
▪Adjacent rotors of a quadcopter must rotate in
opposite direction.
▪Diagonally opposite rotors must rotate in the same
direction, to provide yaw stability.
▪Pitch or yaw can be achieved by varying the rotor speeds,
i.e., by increasing speeds of two rotors while decreasing
speeds of the other two.
▪Once the pitch is altered, the lift vector tilts away from
the vertical, causing a translational motion.
weight
Rotor thrustLift
Forward thrust

9. Dynamics of a Quadcopter (continued)
▪Pitching ▪Yawing

10. Dynamics of a Quadcopter (continued)
What if the adjacent rotors rotate in the
same direction?
▪This will generate a pitch coupled with
yaw motion, when only the pitch control is
applied.
▪Therefore, a pure pitch or pure yaw control
cannot be obtained.

11. Electronics of a Quadcopter
▪ESC : Electronic Speed Controllers
▪Brushless 3-phase motors
▪Flight controller (with on board MPU sensors)
▪Receiver (n-channel) and Telemetry
▪Power supply source (battery)
▪GPS and magnetometer

12. Control system of a Quadcopter
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PID controller:

13. The End
Thank you
- Blesson Easo Varghese