This document proposes a drone-based system for inspecting bridges using 3D printed components. It describes a landing gear system that allows drones to perch on bridge structures for extended inspection times. Rotor shields are also designed to protect drones from collisions. Carbon fiber materials printed on a Markforged printer are used for strength and lightweighting. ABS shields printed on a Makerbot can be cheaply replaced if damaged. Financial analysis estimates the system could capture 0.5-1.5% of the $7.5 billion annual bridge inspection market in 5 years, yielding over $3 million in annual profits.

1. Society of Manufacturing Engineers
Direct Digital Manufacturing Competition
Inspector Drone
Presented by:
TitoArana:Tito_Arana@student.uml.edu
Jordan Castillo: Jordan_Castillo@student.uml.edu
Michael Gager: Michael_Gager@student.uml.edu
DanStella:Daniel_Stella@student.uml.edu
JoanelVasquez:Joaneil_Vasquez@student.uml.edu
AcademicAdvisor:
Dr. Stephen Johnston: Stephen_Johnston@uml.edu

2. 2
http://www.dispatch.com/content/stories/national_world/2012/02/05/u-s--bridge-inspections-vital-but-pricey.html
Abstract
Unmanned Aerial Vehicles (UAV) are designed to perform various task from recreational to industrial
use. This design will offer an alternative method to the way bridges are currently being inspected. Utilizing the
versatility of UAVs. With the ability to print carbon fiber using the MarkForged series of 3D printers, this
design is made possible. The design is based on custom made landing gear and rotor shields 3D printed to
extend the deployment time of UAVs. Seeing the potential of 3D printing and UAVs to aid with bridge
inspection, this project evaluates a current technology and put to practice as safety and effectiveness as a tool
for bridge inspection.
Social and Environmental Impact Analysis:
The aging infrastructure of U.S. roadways is a well-documented issue, with bridges in particular
receiving a C+ grade from the most recent
Infrastructure Report Card1 published in
2013 by the American Society of Civil
Engineers. Bridge inspections are a crucial
part of deciding which bridges need
replacing, repairing, or upkeep. With this
in mind, the choice was made to design a
component that allows drones to be used
during bridge inspections. Bridge
inspections can cost anywhere from
$15,000 to well over $100,0002
depending on the type of inspection
required and type of bridge. For this
report an inspection is assumed to be
$25,000. A large portion of this cost
comes from the way in which bridges are
currently inspected. This includes hiring a
large crane to drive on top of the bridge
deck. A team of engineers or licensed
inspectors use the cherry picker basket
operated by the crane to drop over the
side of the bridge in order for the Figure 1: Comparison of Current to Drone-Based Inspection Method
inspector to visually assess the condition of the bridge. There are two primary concerns in this method. The
first concern being that this method does not give full access to underneath the bridge deck. If the crane arm
extends too long underneath the bridge deck, there is a tipping hazard. The second fault is that this method
requires at least a portion, if not all, of the bridge to be closed to traffic. This increases traffic in other areas
and also has a cost associated with it due to shipping and receiving delays.
Using drones to inspect bridges removes the need to shut down travel lanes because it can be
operated remotely, requiring one on-site operator rather than a team of licensed inspectors. A drone also
removes the need for inspectors to be supported by a crane. This means there is no human life in a hazardous
situation, and the cost associated with hiring a large crane, operator, and traffic detail becomes unnecessary.
1
http://www.infrastructurereportcard.org/a/#p/bridges/overview

3. 4
http://store.makerbot.com/replicator
Drones do come with their own limitations, the first being flight time and the second being stability and
collision.
Design
In order for a drone to be a viable option we must minimize the limitations. In order to maximize flight
time a set of landing gear was designed so that the drone can fly to the required location, deploy the landing
gear between two I-beams underneath the bridge deck, and turn off the motors controlling the rotors while
perched. Stability of the drone is heavily reliant on the operator. In order to assist the operator, the team
designed a set of rotor shields so that during a collision the rotors are not stopped or damaged, preventing
them from producing the necessary thrust.
The landing gear consists of 4 arms that are 36” long and are extended and retracted with the use of a
power screw and linkage system. It is designed to work with bridges that have a distance between support
beams from 1.5 - 2 meters. In order to accommodate the varying sizes of bridges the arms are built in 12”
segments with quick disconnects to easily add or remove them.
In order to prevent flight failure, shields have been designed to be placed around each of the 6 rotors.
These shields can be clipped in to the existing frame. The area of these shields are small enough to minimize
airflow disturbance while maintaining the structural integrity necessary to shield the rotor from impact. Due
to the inexpensive nature and thin frame of the shields they are considered replaceable and new ones can be
printed as the need arises.
Justification of DDM Choices and Materials
A material with a high specific strength is required for the landing gear. Carbon fiber is a common
material in the aerospace industry for this very reason. Not only will it give the needed structural support, but
it also minimizes the added weight to the system. A MarkForged Mark Two3 series printer allows us to print
carbon fiber layered with nylon. A single layer from the Mark Two is 0.1 mm thick, the truss in the landing gear
arms are 1.25 mm thick. This was done to prevent buckling, even though there is a large safety factor in
vertical bending. This material has a tensile strength similar to aluminum, but at a much lower weight cost.
The printer also
allows us to maximize
the tensile strength of
the material by
orienting the fiber in
the required
direction. The shields
are printed using a
Makerbot Replicator4
and constructed out
of ABS. The relatively
inexpensive cost of
ABS allows for this
part to be easily and Figure 2: Stress Analysis of Landing Gear
3
https://markforged.com/

4. cheaply replaced when it fails. This part is expected to see failure since it is meant to absorb the collision in
place of a rotor.
Cost-BenefitAnalysis:
As of 2013 there are
over 600,000 bridges in the
National Bridge Inventory5
database and they all require
routine inspection at a
maximum of every 24
months. Assuming an
average cost of $25,000 per
inspection and a total of
300,000 bridges are
inspected per year, this leads
Table 1: Cost-Benefit Analysis
to a target market of $7.5 billion annually. The goal is to start out with 0.5% of this market, or to have our
design used for 1,500 bridge inspections. Assuming a scenario where a different drone is used for each bridge
1,500 complete drone modification kits need to be manufactured in the first year, or roughly 4 per day. A
modification kit includes 4 arms and 6 shields. To manufacture a modification kit takes 24 hours per arm, and
4 hours per shield. A total of 16 MarkForged Mark Two printers and 4 Makerbot Replicators are necessary to
achieve this production volume. A complete landing gear setup costs $257.60 in carbon fiber and nylon to
produce. A full set of rotor shields will include 6 shields and cost $5.76 in ABS to produce. A stepper motor is
required to drive the arms into position and costs $50.00. The total production cost of each modification kit is
$313.36. If each modification kit is sold for $1,000 than an annual profit of $1.03 million is forecasted.
Table 2: Savings per Day of Inspection
Selling a drone
modification kit for $1,000 is
reasonable based on the cost
savings for an inspection.
Using a drone saves roughly
$1,800 for the crane and
operator, $400 for the traffic detail, and $3,200 in on-site inspectors, or a total of $5,000 per day of inspection.
We believe purchasing the recommended drone and modification kit for a total of $2,000 is well worth the
$5,000 per day savings.
The company expects to take at least another .25% of the market annually. This will lead to a 1.5%
share of the market in 5 years, or have our drones used for 4,500 bridges. A profit of $3.09 million annually is
forecasted in this scenario. Once production volume reaches 10,000 shields annually the manufacturing of
these will likely be switched to injection molding rather than 3D printing in order to reduce cost and increase
production speed. Currently the designs are only fitted for DJI FlameWheel F550 Hexacopter model. As the
company expands we aim to increase the number of models that our landing gear can fit and even build
custom gear on an individual basis. This will also increase the size of bridges that are compatible with our
design and the type of test sensors that can be used in order to keep pace with emerging technology.
5
http://america.aljazeera.com/articles/2013/9/16/many-us-bridges-arestructurallyunsoundsaysnewreport.html
Costs Amount Desicription
Overhead $500,000.00
Includes Rent, Printer Costs, Printer Maintenance, Employee Salaries,
Employee Benefits, Marketing
MarkForged Printers $88,000.00 16 Mark Two Printers @ $5,500 each
Makerbot Printer $5,800.00 2 Replicator Printers @ $2,900 each
Motor $50.00 1 Stepper to Drive Power Screw
Carbon Fiber $240.00 Cost for Complete Set of Landing Gear
Nylon $17.60 Cost for Complete Set of Landing Gear
ABS $5.76 Cost for 6 Rotor Shields
Producer Cost $313.36 Total Cost per Drone Modifcation Kit
Price Sold to Customer $1,000.00
Profit per Set $686.64
Complete Sets Printed Annually 1,500
Annual Profit $1,029,960.00
Savings Amount Descirption
Crane $1,000 Daily Cost of Crane
Crane Operator $800 8 hours for Operator @ $100/hr
Traffic Detail $400 8 hours for Police Officer @ $50/hr
On-site Inspectors $3,200 8 hours for 3 Inspectors each @ $100/hr
Daily Savings $5,400