The basic objective of the student's work this quarter was to make an in depth examination of the design concepts used on the lunar vehicle 'The Enabler'. Several changes were made to the vehicle including a redesigned wheel, a more compact boom and a reduced articulation angle. The vehicle's final dimensions were determined through an optimization process by defining mathematical equations for several of the vehicle's defined objectives. These included the ability to scale a one meter object, traverse a one meter crevice, and maintain a wheel-to-wheel clearance of three inches while at maximum articulation. The final dimensions of the vehicle were used to construct an approximate 1/4 scale model of the chassis and wheels. The boom, however, was constructed on a 1/5 scale (from the original design). This was due to the redesign of the boom and the limitations of the constructing material and PVC fittings

Bess, David

Fye, Stephen

Gale, Thomas

Haldopolous, Dean

Looney, Michael

Milam, Ken

Smith, Dan

Sosebee, Frank

English

NASA Technical Reports Server

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NASA-CR-192061
THE ENABLER:
A REEVALUATION OF DESIGN CONCEPTS
AND CONSTRUCTION OF A SCALED MODEL
David Bess
Stephen Fye
Thomas Gale
Dean Haldopolous
Michael Looney
Ken Milam
Dan Smith
Frank Sosebee
Professor: J. Brazell
8 June 1992
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The George W. Woodruff School of Mechanical Engineering
Georgia Institute of Technology
Atlanta, Georgia 30332-0405
https://ntrs.nasa.gov/search.jsp?R=19930008850 2020-03-17T09:16:45+00:00Z
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Table of Contents
Abstract ............................................................... I
Introduction ....................................................... 2
Concept Redesign ............................................... 3
I. Wheel .............................................. 3
II. Boom .............................................. 4
Optimization ..................................................... 5
I. Equations ...................................... 6
II. Program ........................................ 7
III. Data ............................................... 8
Final Dimensions .............................................. 10
Technical Activities ......................................... 11
Acknowledgments ............................................ 12
The basic objective of our work this quarter was to make an in-
depth examination of the design concepts used on the lunar vehicle
"The Enabler". Several changes were made to the vehicle including a
redesigned wheel, a more compact boom and a reduced articulation
angle. The vehicle's final dimensions were determined through an
optimization process by defining mathematical equations for several
of the vehicle's defined objectives. These included the ability to scale
a one meter object, traverse a one meter crevice, and maintain a
wheel-to-wheel clearance of three inches while at maximum
articulation. The final dimensions of the vehicle were used to
construct an approximate 1/4 scale model of the chassis and wheels.
The boom, however, was constructed on a 1/5 scale (from the
original design). This was due to the redesign of the boom and the
limitations of the constructing material and PVC fittings.
INTRODUCTION
"The Enabler" is a concept vehicle which uses several new ideas
in lunar technology. It is a work vehicle which can be used for many
applications in space including construction, demolition, and
transportation. One of the most important features of the vehicle is
that all of the subsystems that run the vehicle are self enclosed. This
allows the vehicle to be operable in the harsh environments that are
encountered in space. The vehicle's morion is controlled by
articulation joints which provide the vehicle with the ability to steer
and more importantly, to pitch. This allows the vehicle to traverse
landscapes that were previously not traverseable. The wheels of the
vehicle are also an important concept. They not only provide the
drive force to move the vehicle, but also provide the suspension
qualities for the chassis. Another important feature of the "Enabler"
is the boom. The boom has been designed with the ability to
withstand forces of ten pounds or less in any direction. It is also
equipped with a tool interface which can grab a number of tools from
a magazine and use them to perform a variety of tasks. With all of
this in mind, our group set out to evaluate these design concepts in
detail.
Wt-II_EL CONCEPT REDESIGN
From last quarters wheel design, an issue was brought up
about the clearance the wheel extension would have if some object
with a size greater than the chassis clearance was come in contact
with. The figures on the following pages show the design conceived
in the previous quarter and this quarter. The previous design
consisted of a flexible wheel with an initial conical section (attached
to the chassis) connected to a cylindrical section. The wheel
extension was long and could bottom out if the vehicle was to run
over a large object. The other problem seen with this design was the
possible lack of traction in loose soil or when climbing a steep hill.
To compensate, the wheel was redesigned to the shape seen on
the next page. This design allows more wheel to be in contact with
the surface. Also, the extending of the conical shape and the
reducing of the wheel extension helped reduce the weight of the
wheel assembly, i.e. there will be less "chassis" (with heavy machine
parts) and more wheel (lighter than chassis material and internal
parts). The new shape also allows the ribs to be extended the full
length of the wheel so that more traction can be obtained. Extending
the wheel to this shape relieves the problem of bottoming out as
seen with the previous design. Instead the new wheel will be able to
climb over the object with the wheel still acting as a suspension for
the whole vehicle.
vv
ORIGINAL WHEEL
_T
v
v
NEW WHEEL
CONCEPT
i
,,
V
BOOM CONCEPT REDESIGN
With the reduction in the size of the chassis and wheels, it was
also necessary to reduce the size of the boom. At first, the boom was
designed to be the length of the chassis and the length of the wheels
on the front and back of the vehicle. To optimize the size of the
boom, the length was shortened to the center axis of both the front
and rear tee sections. Since the length of the chassis was shortened,
the overall length of the boom was reduced by approximately 4 and
1/2 feet. With this reduction, the foUowing parameters were
affected:
lo
2.
3.
4.
S.
Less weight
Smaller Moments
Less stress on chassis
Tipping of vehicle reduced
Smaller work envelope
From the optimization of the chassis and the boom, the vehicles
dimensions were scaled down so a working model could be made.
4
OPTIMIZATION
The optimization of this design minimizes the kinematic forces
created on the Enabler and maximizes its use in a lunar environment.
The following constraints were used in the design:
CLIMB AN OBSTACLE 3' IN HEIGHT
TRAVERSE A 1' CHASSIS CLEARANCE WITHOUT
ARTICULATION
HAVE A CHASSIS CLEARANCE OF 3" IN ITS WORST CASE
ARTICULATION
MINIMIZE GAP BETWEEN TIRES TO 8"
MINIMIZE AXLE TO AXLE LENGTH (W)
MAXIMIZE ARTICULATION ANGLE (A)
To perform the optimization analysis of this project, several
variables were considered. As shown below, the vehicle was
designed with four variables in mind. Those were:
• T
• D
• W
• A
VEHICLE WIDTH
WHEEL DIAMETER
AXLE TO AXLE LENGTH
ARTICULATION ANGLE
From the model and the governing equations, a change in one
variable may be both beneficial and detrimental to the design. For
example, as the articulation angle increases, the turning radius of the
Enabler decreases, which is a desirable effect. However, as the
articulation angle decreases, the distance from wheel to wheel
decreases. This is an undesirable effect because a minimum wheel
Vgap of eight inches is required. Similarly, as the wheel diameter
increases, the climbing ability of the Enabler is increased, but the
turning radius is decreased. Below are a list of the dependent
variables in the constraints.
• R
• O1
• 02
• C
• G
TURNING RADIUS
OBSTACLE HEIGHT 1
OBSTACLE HEIGHT 2
CLEARANCE
WHEEL GAP
With four independent variables, there are an infinite number
of possibilities that will satisfy the constraints. To narrow down the
possible number combinations the vehicle width, T, was set equal to
two meters. This number was chosen to ensure easy transport of the
Enabler in a typical trailer. To further narrow down the possible
number of combinations, the articulation angle was chosen to range
from twenty to thirty degrees.
From this point, it was necessary to analyze the design from a
mathematicai standpoint. Five basic formulas were found solving for
the turning radius, wheel gap, and two obstacle heights.
• TURNING RADIUS
R= W/2(TAN(A/2))
• WHEEL GAP
G = W-D-(T/2 SIN(A)) - W/2(1 - COS(A))
• CLEARANCE
C = D/2 - W/(SIN(A/2))
OBSTACLE HEIGHT 1
O1 = W/2(SIN(A/2)) + .1568
vv
OBSTACLE HEIGHT 2
O1 -- W/2(SIN(AJ2) + SIN(1.5A)) + .1568
The formulas shown are dependent on only two variables, the
articulation angle, A, and the wheel diameter, D. The optimal design
size of those two variables are the values that meet all the
constraints. In other words, all the possible combinations of W and D
needed to be applied to the formulas. The output for each dependent
variable then has to be weighed against aU of the other dependent
variable values using other Independent variable sets. This was
done with a simple program written in Basic.
With the program shown below, three nested loops allowed for
the articulation angle to be varied from twenW to thirty degrees,
while the wheel diameter varied from 1.07 meters to 2.07 meters,
and while the vehicle width varied from 1.4 meters to 2.4 meters.
The program produced a list of all combinations that met all the
constraints. The program in effect reduced hundreds of
combinations to twenty combinations.
20
30
4O
5O
6O
70
8O
9O
IO0
110
120
130
T=Axle Length
W=Wheel Base
D=Tire Diameter
A=Articulation Angle
R=Turning Radius
O 1=Obstacle Height1
O2=Obstacle Height2
C=Clearance
G=Gap
********************** Loop Parameters **********************
T=2
For W= 1.2 to 2.4
7
140
150
160
170
180
190
200
210
220
230
240
250
260
270
For D= 1.07 to 2.07
For A= 20 to 30
********************** Number Crunching ********************
R = W/2(TAN(A/2))
G = W-D-(T/2 SIN(A)) - W/2(1 - COS(A))
C = D/2 - W/(SIN(A/2))
O1 = W/2(SIN(A/2) + SIN(1.SA)) + .1568
O1 = W/2(SIN(A/2)) + .1568
********************** Constraints *****************************
If O2>1 and C>.08 and G>.13 then Print W,D,A,R,G,C,O1,O2 else
240
Next A
Next D
Next W
End
The listed program produced the following data:
Axle Wheel Tire Art. Turning Obstacle Obstacle Clear.
Length Base Diameter Angle Radius Height 1 Height 2
2 1.8 1.07 29 3.48 0.593 1 0.3096
2 2 1.07 26 4.33 0.595 1.01 0.31
2 2 1.07 27 4.16 0.6107 1.03 0.3015
2 2 1.07 28 4.01 0.6261 1.06 0.293
2 2 1.07 29 3.87 0.6415 1.09 0.2846
2 2 1.07 30 3.73 0.6566 1.12 0.2762
2 2.2 1.27 25 4.51 0.6085 1.01 0.4185
2 2.2 1.27 26 4.33 0.6243 1.04 0.41
2 2.2 1.27 27 4,16 0.6339 1.06 0.4015
2 2.2 1.07 28 4.01 0.6554 1.09 0.393
2 2.2 1.07 24 5.17 0.6041 1.03 0.3063
2 2.2 1.07 25 4.96 0.6215 1.06 0.2969
2 2.2 1.07 26 4.76 0.6388 1.09 0.2875
2 2.2 1.07 27 4,58 0.656 1.12 0.2782
Wheel
Gap
0.1323
0.39
0.367
0.343
0.3198
0.296
0.2137
0.1904
0.167
0.1434
0.62381
0.6043
0.5803
0.5561
From these numbers we were able to identify an optimal sizing. The
first row of numbers produced by the program were the smallest in
wheel base, tire diameter and axle length. These numbers will
therefore produce the smallest kinematics forces on the Enabler
allowing for minimum dimensions of chassis components. This will
8
also minimize the vehicles overall size for transport and weight.
Another method used to optimize the sizing was accomplished
by using three-dimensional graphing. On the X and Y axis, the axle-
to-axle length (W) and the articulation angle (c_ were plotted. The
five dependent variables were plotted on the Z axis. This created
five three-dimensional curves with our optimal ¢0 and a located at
the lowest peak on the Z axis at the intersection of all the curves.
This method produced data that was concurrent with the data listed
above.
With an axle length of two meters and an articulation angle
(maximum) of 29% the resulting final dimensions (see following
page) gave the Enabler a minimum turning radius of approximately
3.5 meters with all other constraints met.
vFINAL DIMENSIONS
From the analysis of the parameters as described above, the
final dimensions of the main chassis parameters are shown below:
18 IN) O.]3.0.4572 M
2.0 M
(78.74 IN)
1.07 M O.D. (42.126
L 15d
1.8 M
(70.87 IN)
_!i!i!:!i!i!
::::::::::::
10
VTECHNICAL ACTIVITIES
The 4192 class made two trips to surrounding technical service
shops this quarter to get "hands-on" experience about a few aspects
of the engineering profession. Jack Seay's design consulting firm
works on projects handed to them from larger corporations to
implement or improve the design of a product or part. Peel's
Technical Service is a machine shop which produces parts for larger
corporations. Both trips were similar in that they both incorporated
ideas and knowledge learned from the Mechanical Engineering field.
While the Seay Group was more design oriented, the visit to Peel's
showed more of the hardware involved in the creation of a product.
We would like to thank Jack Seay and William Peel Jr. for their
knowledge and experience they shared with us. Each trip was very
informational and an interest to all 4192 members. The information
provided gave us a view of what it takes to successfully design a
product and how to convey the design to the machinist so that his
understanding of it is clear and complete. These activities are
beneficial to students because they help provide the insight needed
to make them better engineers.
11
WACKNOWLEDGMENTS
v
We would like to thank Mr. Brazell for his sponsorship of this
project and our T. A. Craig Campbell for his assistance. We would
also like to thank the National Aeronautics and Space Administration
for providing the funds for this project.
12


The Enabler: A reevaluation of design concepts and construction of a scaled model

The Enabler: A reevaluation of design concepts and construction of a scaled model

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