Rescue Hexacopter Project

 

Design

The design process begins with a review of the design constraints and considerations. 

The first consideration is that the craft must be capable of lifting itself and a 6 lb. payload.  This means that the total lifting capacity for the craft will be close to about 20 lb.  This will be important during the operation phase as we test the design.  So what does it take to lift 20 lbs. with a hexacopter? 

To answer this, we need information on the flight characteristics of multi-rotor craft. Multi-rotor craft have been around since the 1930's but were notoriously hard to maneuver and land using the standard controls of the day. It wasn't until the computer age, that they returned to popularity.

The major problem with the multi-rotor craft is that they are inherently unstable and require minute adjustments to keep the craft in stable flight. Before computers, this was extremely difficult. Now there are numerous manufacturers of flight controllers which allow novice flyers to easily control a multi-rotor craft. We will discuss the flight controllers we looked at in the Production phase.

The flight controller is probably one of the single most important components of this project as it will allow us to simply fly the craft while the onboard gyroscope keeps the craft stable. Even so, we need to understand the basics of multi-rotor flight.

There are three fundamental flight parameters which we need to know:

Yaw, Pitch, Roll

On a multi-rotor, these changes must be accomplished using variations in the speed of the rotor. By increasing the speed of the rear rotors and reducing the speed of the front rotors, we can change the roll of the craft and propel it in a forward direction.

To move the craft right, the speed of the left rotors are increased and the speed of the right rotors are decreased changing the pitch of the craft and moving it to the right. The opposite is done for moving the craft left.

To rotate the craft right upon the horizontal plane (maintaining its pitch and roll) the speed is increased on all clockwise motors and decreased on all counterclockwise motors, causing the craft to rotate in place changing the yaw of the craft.

The propellers on a multi-rotor craft also have to produce the thrust to lift the craft. As the craft changes the yaw, pitch, and roll it also changes the altitude of the craft. To keep the craft level, any change in yaw, pitch, or roll also requires a change in the thrust of the craft. Again, the modern flight controller makes the necessary adjustments in speed to compensate for all flight characteristics.

Types of Multi-rotors

Tri-copters - Tri-copters, as the name implies, are composed of three rotors. Tri-copters are very nimble and are a favorite for acrobatics. The layout of the rotors is usually in the "Y" format, with the tail rotor usually controlled by a servo for thrust vectoring. The use of clockwise rotors is optional. The major drawback is payload capacity

Quad-copters - Quad-copters have four rotors arrayed in one of two different configurations, "X" or "+". In the "X" configuration, the rotors are arranged so that two rotors are in the front of the craft and two are in the rear of the craft. In the "+" configuration one rotor is in front, one to the rear, one to the left and the last one to the right. Quad-copters are very popular as they are nimble and can be used for many purposes. The DJI Phantom is one of the most popular commercial quads available. It is designed to carry the compact Go Pro series of cameras.

X and + Quads

Hexcopters - Hexcopters or Hexa-copters have six rotors arrayed in one of three different configurations, "X", "+", or "Y6". In the "X" configuration, the rotors are arranged so that two rotors are in the front of the craft and two are in the rear of the craft. The other two rotors are directly right and left. In the "+" configuration one rotor is in front, one to the rear, two to the left and the last two to the right. In the "Y6" configuration, the rotors are arranged like the tricopter, with one clockwise rotor on top and one counter clockwise rotor on the bottom. Hexcopters are not as nimble, but can carry larger payloads and are extremely stable for aerial photography.

Hex X and Hex +

Y6 Rotation

Octacopters - Octacopters have eight rotors arrayed in one of three different configurations, "X", "+", or "Y8". In the "X" configuration, the rotors are arranged so that two rotors are in the front of the craft and two are in the rear of the craft. Two rotors are directly right and left. In the "+" configuration one rotor is in front, one to the rear, three to the left and the last three to the right. In the "Y6" configuration, the rotors are arranged like the quadcopter, with one clockwise rotor on top and one counter clockwise rotor on the bottom. Octacopters are extremely stable for aerial photography, can carry huge payloads, but have the shortest flight times due to the increased electrical energy needed to power eight motors.

X and + configurations

Octa Quad

 

For this project, we decided to go with the Hexacopter in the "X" configuration. We chose the hexacopter for its lifting and stability.

 

 

 

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