Executive Summary - Senior Design - University of Idaho

ukrainianlegalElectronics - Devices

Nov 2, 2013 (3 years and 7 months ago)

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Fall
2008

Tim Palmer, Matt Cerro, Mark Pennington,
Eli Henson, Nick Yankee, Achala Akuretiya,

David
Mehaffey

robo
-
horizon@uidaho.edu


Design Report

1


Contents

Executive Summary

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2

Background

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3

Problem Definition

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3

Project Plan

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4

Concepts Generated

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5

Catapult

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5

Electromagnetic Launcher (EML)
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6

Sling

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8

Concept Selection

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10

System
Architecture

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11

Future Work

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12

Appendix A
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13




2


Executive Summary


On one of the next missions to the moon NASA would like to take soil samples in the
bottom of some permanently dark craters. Unfortunately, little is known about the terrain in
the bottom of these craters and NASA feels that a traditional rover design wou
ld be too risky.
Instead the plan is to place a Lander in the bottom of the crater then “launch” sensors out in a
60 meter radius circle. Our team was given the task of creating this launcher.


Currently the three methods we have considered are, the el
ectromagnetic (
EML
)
Launcher, the catapult and the sling. The
EML
uses a magnetic flux to generate the necessary
launching force. Its main advantages are the ease with which the length of the launch can be
changed electronically and the lack of moving pa
rts. Its main disadvantage is its complexity; it
still has not been successfully demonstrated. The catapult uses a method proved in the Middle
Ages, using a combination spring and lever arm to supply the launching force. Its main
advantage is that the d
evice has been used for centuries so most of the kinks are already fixed
and most of the work has already been done. The main disadvantage is that it is nothing new
so it isn’t very impressive. The Sling had the advantage of simplicity and a proven desig
n, like
the catapult. Unfortunately it needs to be level and gives up the advantage of a 45


trajectory
requiring the initial velocity to be four and a half times the size.


Due to time limits and design inefficiencies the sling prototype has been discont
inued.

Also due to the lack of a working prototype the
EML

has been sidelined.

Thus the catapult
design has been chosen as the final design choice. Work is still being done on the sidelined
designs but only as backups and due to private interests.



3


Ba
ckground


“The Moon is the first milestone on the road to the stars.” This quote by Arthur C. Clark
captures the very essence of Robotic Horizons’ exi
stence. Robotic Horizons, a University of
Idaho capstone design

team
, has been tasked

by NASA to develop a device to
deploy

sensors
with the intent of locating
hydrogen on the Moon. It is speculated that there is hydrogen
within the dust on the Moon’s surface.
Due to the low gravity,
gasses escape the atmosphere
of the Moon
easily.

NASA

wants to search within the craters of the moon where the possibility
of finding hydrogen is
much higher
.
The ultimate goal is to

harvest hydrogen on the moon in
order to create habitats suitable for humans to work in. This would make launching missions
to
Mars much more feasible as the Moon could be used as either the launching point, command
point, or a staging point. There are many more possibilities for scientific activity upon discovery
of hydrogen on the Moon.

NASA plans
to land

a stationary plat
form within one of the larger craters. This is where
the design by
Robotic Horizons
would be utilized
.
The design will deploy sensors throughout
the crater collecting environmental samples
. These sensors will use

a
method
, such as mass
spectrometry, to
search for hydrogen. The design of the sensors, however
, is not within the
scope of this

project.

Problem Definition


In the near future,

NASA plans to set down a
Lander

into some of the deep
,

permanently
shadowed craters on the moon.
Their desire is
to take soil samples looking for hydrogen
around the
Lander’s

location.
Due to limited information regarding terrain and conditions
present,
NASA does not
expect

a rover to be able to maneuver
successfully
.


With these conditions in mind the Robotic Lunar

Exploration Project

(
RLEP
)

Instrument
Launcher was envisioned. A device is needed to launch a sensor,
one kilogram

in mass and
approximately
1
6

cubic

centimeters

in volume, up to
60 meters in any direction under lunar
gravity. The device will launch fro
m a platform
up to one

meter
above ground level
. The
platform will have a base
40 x 40

square
centimeters

and a maximum height of
61

centimeters
.
The current plan calls for 10 launches for the proof of concept
;

the
final
design
is required
to
4


have the ca
pability
of

100 launches

or more
.

See Appendix A, Figure 8: House of Quality for a
complete list of design criteria.



Due to this mission being

slated for the moon
,

certain

constraints need to be
mentioned. The
most significant cost of the final design

will be

weight
.

This means that the
cost of materials and construction are almost negligible
compared to the cost of transporting
the instrument to the Moon
. Also
,

the instrument will need to be self powered because of the
permanently shadowed nature of

the craters.

Project Plan


In order to complete this project
on schedule
,
we

conduct

a minimum of

two weekly
meetings. The first wee
kly meeting is held on Thursday

at 3:30pm. This meeting is for team
members to discuss ideas, problems
, current

issues, a
nd come up with solutions. It also is to
inform the team of progress made during the week. The second team meeting is held
Friday

at
11:30am. The purpose of this meeting is to update the graduate mentors and the faculty
advisor as well as to receive gui
dance and project recommendations.
We

also
me
e
t on our

own
time to work on team assignments and accomplishing goals and tasks.


The first quarter of the semester was devoted to identifying the problem statement,
receiving as much instruction and guidance
as possible, and thoroughly reviewing the project
goals. The next half of the semester was devoted to planning.
We

created many design ideas
and focused on the pros and cons of each idea. After austere review of each of the de
signs, we

decided to build
three prototypes. The last quarter of the semester was dedicated to design
improvements and the manufacturing of the prototypes. The schedule of deadlines and
planning can be seen in
Appendix
A
, Figure
11
.

Our team

is comprised of
four

mechanical and
th
ree

electrical engineering
students
.
This allow
s

the team

to
divide

into smaller groups and work on issues where
an
individual
’s
e
xpertise lies. The responsibilities of each team member are nearly the same. Respect for
other’s ideas and a willingness to accomplish team goals are required by all. A willingness to
offer positive input to the team

is a must.
T
he overall responsibili
ty of each and every team
member and
the

team collectively, is mission accomplishment.

5


Concepts Generated

Catapult

One of the forefront concepts the group has decided to investigate further is the
Catapult.
Historically

the catapult
has proven to be

a ver
y effective, accurate, and efficient way
of hurling an object over a distance. With this design, instead of re
-
inventing the wheel, we’re
just refining an already good idea.

Figure 1 shows a sketch of the initial prototype.


Figure
1
: Catapult Prototype

What we like about the Catapult is its simplicity.
B
uilding design
s and mathematical
models
including

the physics of a catapult

are readily available
.
There are relatively few
variables to consider when dealing with the operati
on of a catapult when compared to other
concepts.
As compared to the Sling model it is not limited by other objects on or around the
platform
.
The only power required for launching is a
motor
used
to pull the arm back
.

As for
re
-
loading, the design make
s this very simple. The very act of retracting the sensor array pulls it
back into the cup of the catapult

as seen in
F
igure 1 (above)
.


Another aspect of the Catapult design is
its

ability to use and or interchange different
sources

of launching force
. The main option right now is a simple spring which will pull the arm
up rapidly. This will facilitate rapid prototype production as well as allow us to refine some of
the
details of the design

while
minimizing complexity
. In addition to the spring

we
are

looking
6


into an electromagnet
ic

design. The electromagnet

would be charged very briefly producing

a
very strong magnetic field which would
repel

another electromagnet or permanent magnet
.

The final major consideration for the Catapult was the power c
onsumption. Regardless
of whether or not the Catapult uses a spring or electromagnet, it is still projected to use
a
minimal amount of power
.
This is a strong benefit

as one of our
primary design

restrictions is
battery life. The equations used to calcu
late power for the Catapult can be found in
Appendix
A, Figure 14
.

Electromagnetic Launcher

(EML)

The electromagnetic launching system was
inspired

by

numerous different sources. Rail
guns have often been considered for explosive
-
free projectile launchi
ng. A favorite
demonstration of many physics departments and garage experimenters involves launching an
aluminum plate from an energized coil of wire. Many modern companies are investigating the
use of electromagnetic launchers with a similar apparatus f
or propelling satellites and other
space craft into orbit.
We

looked to these technologies and saw the opportunity to scale it into
a small
, lightweight,

package.


Figure
2
: Electromagnetic Launcher Design


The
EML

concept

consists of wire wound solenoid using a steel core as a highly
permeable flux path. A MOSFET controlled by a Rabbit microcontroller is used to manipulate
7


the discharge pulse.
Multiple

capacitors are connected in parallel to store the charge required
for

firing the projectile. A simple DC to DC converter will be used to step up the battery voltage
to charge the capacitors to the required potential level. The projectile is guided at launch by a
short barrel protruding from the steel core.
Figure 2

is a
n image of the EML concept. Figure 3
reflects the proposed circuit implemented in this design. M
athematical models pertaining to
the specifics of this conceptual design

can be found
in Appendix
A, Figures 15, 16, and 17
.



Figure
3
: EML Circuit Design


The first
advantage of

this

concept
is related to

energy efficiency. Due to the lack of
moving parts, friction
al

losses within the launcher itself are very limited. High power levels are
required for operation, but only for an ex
tremely short duration. In this design a capacitor bank
is utilized to provide storage for the charge

and

to allow
for
a quick discharge

producing

the
large energy pulse. The short pulse width factors in to low average power utilization. Retrieval
and ta
rgeting power consumption are similar to
the
other designs.

The low power
consumption meets

one of our

major design requirements.

Another design
constraint we sought to achieve with the
EML

concept

was accuracy

and
repeatability
. The purely electrical na
ture of the launching mechanism allows for precise
control of the projectile using a microcontroller and supporting hardware. Targeting will be
achieved with a

combination of bearing control,
using a motor and turntable
,

combined

with

varying the discharg
e pulse width by
means

of a microcontroller and MOSFET.

Few friction
8


forces present in the launcher limit the variance of each launch from ideal. This allows for
consistent control using algorithms to account for known variables and targeting
instructions.

Sling

The sling design
utilize
s

rotational momentum
to launch the projectile
. By maintaining a
constant angular velocity
and

increasing the radius between the load and the center of
rotation
,

a significant amount of energy can be stored
.
Th
is design could also

launch multiple
projectiles at one time in a random pattern.

Mathematical models for sling projectile motion
can be found in Appendix A, Figures 12 and 13.



Figure
4
: Sling Design


Some of the benefits of this design are the random launch pattern and
the device
’s
ability to

throw the projectile in 360 degrees without the need of a turntable. Also it has the
benefit of simplicity. The device does not require any complex electronic
aids. A simple motor
controller

can increase or decrease the rotational velocity and another simple motor will reel
the tether in and out.

There are a few problems with this method. The first problem is that it requires a
considerable amount of space

and

would be adversely affected by obstructions near the
platform
. The power cost decreases as the radius of the circle increases.
A nearby obstacle
9


would require
the device to use considerably more energy per launch

due to the decreased
radius.


Another problem is the

device must remain level. The optimal
launch angle

for any
object seeking to travel the farthest distance is
45 degrees
. The current sling
design does not

take advantage of this and as a result requires an initial velocity
over fo
ur times greater

than
other designs
.

Figure 5 is an exploded 3D view of the current prototype sling.




Figure
5
: Sling Design



10


Concept Selection


The following morphological chart (Figure 6) was used to asses each alternative f
or
completion of the process flowchart (Appendix A, Figure
9)

design. From this analysis, three
initial concepts were chosen. The sling, catapult, and EML were selected for further review.


Function

Method

Launch

Electromagnetic
Launcher

Catapult

Telescoping Arm

R/C Vehicle
(Wheels)

R/C
Vehicle
(Tracks)

Retrieve

Cable

Vehicle

Telescoping Arm





Deployment (set up)
(storage)

Self Contained

Assembly







Loading (Re
-
loading)

Mechanical

Magazine(Spring)

Magazine
(Gravity)





Aim
-
controls

Stepper Motor / Microcontroller

Trajectory

Spring
Tension



Target Acquisition

Pre
-
programmed points

User aim by range/direction

Pattern

Launch Distance

Electrical

Mechanical
(Spring)







Guidance Sensors

Laser Range Finder

Baseline Zeroing





Communication

Wireless

Wired
(Umbilical)







Figure
6
: Morphological Chart

At a team meeting three weeks
prior to

Senior Snap Shot Day, it was decided as a team
that the sling
was not

capable of meeting
the

standards. It used too much power and
did not

make use of the optimum

45 degree

launch
angle
.

It

was decided that we would discontinue
research on this
concept to

focus our attention on
production of the Catapult and EML
prototypes.


Our first prototype of the
EML

did not

work as expected. It
attracted

the dummy
projectile

as opposed to
repelling it
. After talking to Dr. Hess, a Professor in Electrical
Engineering, it
w
as suggested that the design could not operate with the switch use
d. It was
determined that a MOSFET used in place of the switch, and operating at the resonant
frequency, would make the device operate
as desired
.

Unfortunately this idea was too complex
to be of use to us, and after much time and effort we still did not

have a working prototype so it
was sidelined.

11


According to the decision matrix, t
he catapult design is the most viable
.
With this in
mind the Electrical engineers will be working on the coding and electronic controls while the
Mechanical Engineers will
be working on improving the catapult design.



Figure
7

Decision Matrix

System Architecture

The first component
of conceptual design

was to analyze and subdivide functional
requirements
into related
categories
.

We started by getting background information on NASA
and the RLEP projects in order
to

better understand the
intent and goals of the project. Our
process flowchart, Appendix A,
Figure
9
, illustrates the all functions that will be implemented
in
the final product.



The second component was to identify a set of design alternatives for each subsystem.
Each

team member
produced

at least 5 detailed sketches of possible designs
.

The point of this
task was to isolate members from each other so the i
deas were as unique and imaginative as
possible. We
did not

want any ideas to be overlooked
,

so there were no
restrictions

for the
design alternatives other than they had to
meet project specifications
.

The third component

was to assign team members to fur
ther explore a selected few
design alternatives
.

Each design alternative needed to be researched for
feasibility
, function,
and relative efficiency
.

The information gathered allowed the team to select a design to carry
on to final production.

Also available at the design review will be our current budget, an end of
semester budget is included in Appendix A, Figure
10.

For simplicity, our design project can be split into three subsystems: targeting,
launching and retrieval.

Targeting will be
accomplished with the use of a microcontroller,
human interface device, and turntable for
angular

control. Launching, discussed throughout
12


this report, will be accomplished by the catapult.

Finally, a motor and tether will be used for
projectile retrieval
.

The primary focus for the Electrical Engineering students in the
spring

semester is the
targeting subsystem. A Rabbit® microcontroller has been ordered for control of the targeting
system. The Mechanical Engineering students have been tasked with findi
n
g an appropriate
stepper motor
.

The launching system is going to be accomplished by the standard catapult
design mentioned throughout this report.

The retrieval mechanism will be accomplished using a
tether and motor. The motor will be triggered by a mot
or controller fed by the Rabbit®
microcontroller. The tether will be fed onto a spool for storage purposes. The spool will be
free to rotate as projectile is released and engaged to the motor at time of retrieval.

Future Work

In the next
semester, our focus will be on control
ling

the
launching mechanism and
building a final prototype for presentation at Engineering Expo 2009. Ultimately our goal is to
design a platform control system (PCS) which will command a turn
-
table, designed to hous
e the
catapult. The PCS will also have an integrated retrieval system.
The majority of

the Electrical
Engineers’

time will be spent on designing
the PCS and programming the microcontroller to
operate the final

design
prototype
.

The Mechanical Engineers’

time will be spent improving the
catapult design and manufacturing a final prototype.

The PCS will be programmed for user
controlled deployment and will also be
pre
-
programmed with a set of
desired

data points
.


The
PCS will then be able to
control deplo
yment of device, deployment, retrieval, and data
acquisition from
the
payload without human interaction. This method will maximize the
flexibility of
our

design
.

13


Appendix A


Figure
8
: House of Quality

14



Figure
9
: Process Flowchart

15



Figure
10
: End of Semester Budget



Figure
11
: Fall Semester Schedule

16



Figure
12
: Sling Math Model


Figure
13
: Sling Graphical Model Angular Velocity Vs. Radius of Cable



17



Figure
14
: Catapult Power Spreadsheet



18



Figure
15
: Projectile Trajectory vs. Initial Velocity at 45 degrees

19



Figure
16
: EML Force vs Turns vs AWG


Figure
17
: Force vs. Distance vs. Number of Turns