Alternate Solutions Rationale

I.                   Struts: Quad Branch and Tri Branch

The structural layout of the multicopter is very important. There are many options for the general layout of a multicopter: quad, tri, single axis, octo, and hexa-copters. However, an analysis of the resource and monetary specifications of each of these options reveals that hexa, octo, and single axis-copters are much more expensive and require higher-grade materials due to the complexity of each design. Therefore, I further researched quad and tri-copters. In addition, the structure will be constructed as an internal skeleton of aluminum or steel punched half channel struts anchored to a custom 3D printed plastic base plate and the corners of an aluminum strut square or triangle, supported by a sub-structure and landing gear; or an exoskeleton of heat formed plastics.

Quad-copters are the more common of the two layouts. A quad-copter generally involves four branches with one motor on each branch. A traditional quad-copter provides great stability and maneuverability at any size. However, quad-copters are more prone to turbulence than its octo and hexa-copter relatives, and cannot operate with one nonfunctional motor, but are capable of surviving a fall with three of its motors operating.

Tri-copters are effective options at smaller sizes. However, it is very difficult to cancel out the torques of the rotors on a tri-copter, which leads to lower stability and requires vibration resistant materials or buffers. Furthermore, the loss of a single motor often results in complete structural failure.

Solutions
Specifications ranked 1-5	Tri-Branch	Quad-Branch
Maneuverable	3-equally maneuverable, however sacrifices in stability make control more difficult.	4-Very maneuverable when piloted correctly.
Stable	2-Torques unbalanced, results in low stability on larger frames and unwanted vibrations.	3-Torques are cancelled by adjacent motors, however moderately low motor count requires larger rotors and lower motor speed, prone to adverse vibrations.
Lightweight	4-Lesser number of branches and motors significantly reduces the weight of the structure	2-More branches and motors, and usually larger size results in much more weight.
Easily Constructed	2-Triangular layout requires specialized parts to construct.	3-Rectangular layout utilizes simple angles and
Adaptable	3-Triangular layout makes modifications or additions difficult.	5-Rectangular layout offers many opportunities for modifications.
Net Score out of 25	14	17

As evidenced by the specification analysis of the tri and quad-copter layouts, the quad-copter design is superior. Overall, the quad-copter provides good maneuverability, better stability, easier construction, and better adaptability. The sacrifices in weight can be overcome using a coaxial motor layout if necessary.

II.                Landing Gear: Individual Pontoons and Ring Pontoon

The landing gear of the multicopter will support the entire structure upon landing. In addition, the landing apparatus must include pontoons that keep the structure above water when landing on a body of water. There for, the landing gear must include some sort of suspension and a means of flotation.

One option for this design problem is to include individual pontoons on each of the legs of the multicopter. This allows for free movement of each suspension system, and thus increases the stability of each landing and takeoff.

Another viable solution is a complete ring pontoon that attaches to each leg of the landing gear. This design restricts the suspension system to a single plain; however, a complete ring makes better use of the available flotation space beneath the multicopter.

Solutions
Specifications Ranked +,-	Individual Pontoons	Ring Pontoon
Flotation Ability	-	+
Stability	+	-
Net Score	S	S

Both designs offer very important features. Thus, I will combine the two designs. A complete ring of flotation material will be suspended below a suspension system and branch off into individual landing pegs covered in the same flotation material.

III.             Prop Layout: Coaxial Motors and Single Motor

In order to achieve flight, the multicopter must have propellers and motors. Depending on the needed lift capacity of the multicopter, each branch can support either one or two motors and propellers.

One motor on each branch achieves a simpler, more reliable system, at the cost of more turbulent flight and less lift capacity. This option also adds much less weight to the frame

Coaxial Motors on each branch increases the risk of system failure due to the deeper complexity of the circuits. However, the doubled amount of propellers provides a smoother flight and the maximum flight capacity in the smallest area. In addition, a quad-copter with 8 rotors is capable of operating with one failed motor.

Solutions
Specifications ranked 1-5	Single motor	Coaxial motors
Reliable	4	3
Stable	3	5
Lightweight	4	2
Effective lift capacity	2	4
Net Score	13	14

Coaxial motors provide great lift capacity and stability, but sacrifice reliability and weight. Single motors offer reliability and low weight, but lose stability and lift capacity with the less motors. Thus, I cannot confidently decide between the two options without further developing the other aspects of the project. Depending on how much weight the quad-copter needs to lift, either coaxial or single motors can be utilized.

IV.             Steering Method: Electrically Controlled and Mechanically Controlled

In order to direct the multicopter to a sampling location and back there must be a mechanism or electrical component capable of steering the vehicle.

Mechanically, the vehicle could be steered with a horizontally oriented propeller that rotates on a vertical axis. The multicopter would move in the direction the propeller faces. This option provides more stability and control over the alternative, but greatly increases the weight of the multicopter.

Electronically, the vehicle could be steered by adjusting the speed of each motor in order to lean the multicopter in the desired direction of travel. This method is by far the most common in multicopter technology. The largest benefit of the electrically controlled option is the lack of any additional weight and the inherent reliability of simplicity.

Solutions
Specifications ranked 1-5	Mechanically Controlled	Electronically Controlled
Lightweight	1	5
Reliable	3	4
Stable	4	2
Net Score	8	11

The electronically controlled solution is desirable because of its simplicity. Also, this method adds no additional weight to the vehicle and offers a faster, more efficient means of transportation that utilizes less battery power.