본문 바로가기

카테고리 없음

[18th Korea Robot Aircraft Competition] Emergency Kit Delivery Drone

System Overview

High-Level Controller : Raspberry pi4

Low-Level Controller : Pixhawk2

Drone used for competition

Maximum Speed 12 m/s Rising/Descending
Maximum Speed
상승 : 3m/s
하강 : 1m/s
Crusing Speed 7 m/s Weight 3.8kg
Length*Width*Height 550*550*300mm Maximum Flight Weight 6.0kg
Maximum Flight time 25 Battery Model Polytronics 10000mah 4s
Li-pi Battery

Spec

 

Mission 

The home -> wp1, wp3 -> home interval performs a curved trajectory using the Artificial Potential Field method.

The rest of the section are using the point-to-point control method

 

Obstacle Avoidance Method (Artificial Potential Field)

 

The Artificial Potential Field consists of the terms Attractive and Repulsive. In the Attractive term, the closer the target coordinate, the lower the potential energy. On the other hand, the closer the Repulsive term is to the obstacle, the greater the potential energy. That is, by setting a path in the direction in which the potential energy decreases, an obstacle may be avoided and a target point may be reached. The distance between the target coordinates and the central coordinates of the no-fly zone is calculated as follows.

 

xgoal and xobs are the positions of the target coordinates and the central coordinates of the no-fly zone, respectively. Through this, the Artificial Potential Field equation is established as follows.

If the distance from the target coordinates is greater than dgoal*, the size of the Uatt linearly increases. That is, the slope becomes constant. If the distance from the central coordinates of the no-fly zone is greater than dos*, the repulsive term does not affect the potential energy. The equation below represents the gradient of the Potential Field.

If the drone's speed is set to the opposite direction of the gradient in the Artificial Potential Field, it will fly along an appropriate route to avoid the no-fly zone.

If the appropriate dgoal*, dos* values are set, the values of k1 and k2 must be determined. If the maximum speed of the drone is Vmax and the coefficient is set as follows, the flight speed does not exceed the maximum speed and a repulsive force is generated at the maximum speed when it touches the boundary of the no-fly zone.

 

r is the radius of the no-fly zone.

When the drone is moved through the created path, PIXHAWK commands the sub-controller using the difference between the current position and speed from the trajectory

 

Real Flight Test log is below

  Horizontal Error(m) Vertical Error(m)
WP1 0.35 0.1
WP2 0.88 1.2
WP3 0.83 1.2

When flying, it can be confirmed that the error is within 2m, which is the threshold value that changes to the next waypoint.

 

 

 

Hardware Design for Mission

Winch under the drone

 

Strong vibration caused by the operation of the drone or malfunction of the winch motor can loosen the fastening bolts of the winch. These defects result in loss of winch components, including emergency kits. As a method to prevent this, flat washers and spring washers were used as shown in the figure below when designing winch. In addition, the nut was inserted so that the nut did not rotate due to shaking.

 

Similarly, an idler as shown in the picture above is attached to maintain the tension of the timing belt to be connected to the pulley. In this case, a load is loaded on the winch frame in the process of maintaining a predetermined tension. To disperse this, several ribs are made as shown in the figure.

 

Separation Device

It has the most important stability of the separation device. It is designed so that the separation device does not drop luggage at any angle. In fact, when experimenting, it was confirmed that there was no problem at all when shaking with force rather than shaking that could occur in drones. The stability of enduring the load is also high. It is designed to withstand the load of luggage by dispersing the load of the separation device rather than the entire blade of the motor.

Because two servo motors are used, the separation device can withstand the weight of the emergency kit leisurely, and the emergency kit is quickly separated. In addition, when performing the order to drop, the closed door not only opens, but also the rear wing following in the form of a waterwheel pushes the luggage away, so it can be dropped reliably.

Since BLE wireless communication was used in communication between emergency kit separators and drones, unnecessary wired communication lines were reduced. Thus, the drone can fly with a lighter weight, and the winch device can operate without worrying about twisting the line.

When the separation device is not operating, hold it strongly so that it is not separated by wind lamps or external force.

 

Safety

1. GPS sensor failure
GPS status can be checked in real time in GCS. Therefore, when GPS reception is problematic or accuracy is not possible, the GCS or the pilot immediately switches to manual control mode.

2. Power Issues
If the battery used for the flight drops below 15%, the GCS will sound a warning, and if the battery drops below 7% without further action, it will switch to Land mode and return to home.

3. Communication Failure
If the controller signal is cut off for more than 0.5 seconds, it will switch to Return mode and return to home. In addition, if the data signal of the upper controller is cut off for more than 5 seconds during automatic flight, it is switched to the Return mode and returned to home.

4 Geo Fence
If Geo Fence is set and the drone is unexpectedly out of the scheduled flight range, it will switch to Return mode and return to home. All return modes are made at an altitude of 30 m, which prevents collisions with structures on the ground.

 

5 Switching control modes
Signals that switch to manual control mode, automatic flight mode, and return mode are assigned to specific channels of the controller, enabling immediate mode switching in emergency situations.

 

As shown in the figure above, it can be seen that if you leave Geo Fence, you return to the inside.

 

 

Flight Video

https://www.youtube.com/watch?v=5CS4bZP0D6A

 

Code

github.com/rladntjd/sunrise.git