Mechanical Engineering Department
BS in Mechanical Engineering
This document describes the design, analysis, and overall goals of the Electric Commuter Multicopter (ECM) Senior Project. It was presented by Bob Addis and Bill Burner to the senior mechanical engineering class of 2015 at Cal Poly, San Luis Obispo. The progress and development of the project are described in detail and to an extent that an individual or group with similar aspirations can construct their own multicopter or expand upon this one. The goal of this project is to create an Ultralight, as defined by FAA Part 103, commuter multicopter vehicle capable of transporting an individual to and from home, work, or school with the potential of becoming a safe, reliable, and efficient alternative to automobiles.
The text contains a background of the project and description of the specific design criteria used to define the function and applicability of the aircraft. Available options of flight, such as planes, autogyros, and helicopters are identified as well as particular components that would be beneficial in ECM’s design. Additionally, the main competitor and reference for the multicopter’s success is the Evolo VC1 because it is currently the sole ultralight manned multicopter. The document moves through the steps used to develop a final theoretical model of the craft. These steps range from preliminary research to detailed analysis and part drawings.
This design of ECM is a 12-propeller aerial vehicle with a traditional quadcopter layout encompassing 4, 3-propeller clusters in a 12’ x 12’ square area. All 3 propellers in a cluster operate synchronously, acting as one. Each carbon fiber propeller is mounted to a JM1S in-runner motor manufactured by Joby Motors, which has a continuous power of 8.2 kW and a constant efficiency of 85%. These motors are powered by 14s LiPo battery packs, and the number of batteries per motor depends on the end-vehicle-weight, so the number of batteries and flight time is tentative.
The aerial vehicle’s structural materials comprises of carbon fiber and 4130 Chromoly steel. There are three components made of carbon fiber: the main arms, motor spars, and propeller rings. The 52” main arms and 22” motor spars are made of unidirectional carbon fiber with a layup schedule of three 0° plies and two 45° plies, surrounding an additional 0° ply in the center. The 52” main arms extend outward from the center mount to the arm mounts. The motor spars extend outward from the arm mounts to the motor mounts, which hold the motor and propeller assembly. The propeller rings are made from a biaxially braided carbon fiber tape with fibers arranged in a +/- 25° configuration. For building the propeller rings, West System’s 105 Resin with their 206 hardener will be used.
The center mount, arm mounts, motor mounts, rings mounts, all brackets and plates are made out of 4130 Chromoly steel. This is based off the premises that the vehicle will experience a significant number of cycles and that steel is a highly reliable material. In addition, lighter metals, such as aluminum, cannot handle the loads for the desired application. Each mount is of circular geometry and fits concentrically into the carbon fiber arms. These steel to carbon fits will be rigidly attached by epoxying the overlapping surface area with 3M Scotch-Weld 2216 2-part epoxy.
The control system of ECM comprises of a Saitek control interface with a Scherrer transmitter, linked via a CompuFly cable. The selected microcontroller is an OpenPilot GCS because it allows for 12 inputs, one input for each motor, and enables an engineer to configure the propeller layout with the built-in software.
Along with the craft’s development, the structure of the team is outlined, providing insight for how tasks are delegated. Task delegation involves assigning individual and team roles with respect to management and finances, as well as approaches for accomplishing more technical tasks within the three main project subgroups: structure, propulsion, and controls.
Additional attention is given to the financial limitations placed on this project. To account for the possibility of not reaching the funding goal for a full-scale prototype, two other options are presented. Results of any of the 3 options will be used to validate the feasibility of this project. However, the disadvantages and advantages of each option are outlined for the reader to realize their value.
To conclude, the theoretical results for a twelve rotor, battery powered, manned multicopter indicate a total expected flight time approaching ten minutes. As such, it will not be until the energy density and weight of small-scale power supplies improve significantly that a vehicle capable of replacing the automobile will be possible. However, this is the first iteration of ECM, and the team believes this project can move forward with great momentum if a full scale prototype is built.