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VMS TILT TABLE
Me 493 Final ReportYear 2015
Group Memb ers
Joel Joiner
Ian Kirkland
Brantley Miller
Jack O’Neal
Nevin Scott
Academic Advisor
Dr. Chien Wern
Executive Summary
Viking Motor Sports (VMS) is a student organization within Portland State
University, which builds formula S.A.E vehicles for competition. The tilt table project was
proposed by VMS students to allow testing of vehicles prior to competition to insure that
the car meets all requirements to compete. The tilt table is used to measure the center of
gravity and ensure the vehicle will not rollover during the race.
VMS currently must wait until competition day to test their vehicles center of
gravity accurately. There are other tests which are both unsafe and inaccurate at
determining the center of gravity. The design the Capstone team choses should be safe,
accurate and convenient for a small team. The table designed allows for the lift of either of
the VMS cars as well as a driver.
The lifting force within the table is a 1” acme screw which is designed to work as a
power screw. The screw is turned through the use of a motor. When the screw turns, the
top part of the table starts to move along a fixed path which tilts the car up to a maximum
of 65 degrees.
This design had several issues which will be explained further in the report. Some
modifications will be made by VMS in order to complete the design. The experience and
knowledge gained from the design process will serve well for future projects.
Table of Contents Page
1. Introduction 1
2. Mission Statement 1
3. Main Design Requirements 2
4. Top Level Design Alternatives 2
5. Final Design 3
Base Design 5
Top Design 6
Screw Design 7
6. Product Design Specifications Evaluation 10
7. Conclusion 10
8. Special Thanks 10
9. Appendix
Appendix A: Product Design Specification 12
Appendix B.1: External Research 14
Appendix C: Top Level Alternatives 16
Appendix D: Finite Element Analysis 19
Appendix E: Technical Drawings 20
Appendix F: Hand Calculations of Forces 22
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Introduction:
Center of gravity (C.o.G.) is the point at which a system behaves as if all its mass
were located at that point. Center of gravity can also be defined as the summation of
moments around a given point. The location of the center of gravity of a vehicle can be
found in a number of different ways and depends on the sum of components and their
location on the vehicle. This P.D.S. document will outline how or tilt table will address the
concerns presented by an unknown C.o.G.
The center of gravity height relative to the ground determines the load transfer of a
vehicle. When a car enters a turn there is a centripetal force that pulls it around the track,
the momentum of the vehicle actuates a load transfer tangent to the direction of its travel,
at this point the vehicle experiences body lean. Body lean can be reduced by lowering the
center of gravity or increasing the roll stiffness of the vehicle.
A vehicle can experience a roll over when the C.o.G. is too high and the load transfer
lifts the inside tires, this is why a tilt table is a good tool for Viking Motor Sports (VMS.) to
have at its disposal, since it can simulate high lateral acceleration. Formula S.A.E., the
governing organization for the competition requires that each vehicle be able to
demonstrate that it can be subjected to a 60 degree angle without experiencing a rollover,
which is another reason why this tilt table will provide a race ready condition for VMS for
years to come.
Mission Statement:
The Capstone team will design and manufacture a tilt table to allow for testing
and analysis of vehicles for Viking Motorsports. The product that will be delivered
will be able to support a car on a table and be positioned at multiple angles. The
product will need to be able to be loaded in a trailer and can be moved and assembled
by 2 people. Upon completion of the product, testing will be performed to confirm
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that the cars can pass the required angle of 60 degrees to be determined safe to race
at competition.
Main Design Requirements:
The PDS documents the criteria that detail the customer needs and constraints.
These constraints will be used for the design process of the VMS tilt table. Listed below are
the main criteria from the PDS. For the full detailed PDS, see Appendix.
Must be able to fit into a 6’ x 8’ trailer
Must be able to be moved and assembled by 2 people
Must have a safety tether as a fail-safe for tipping vehicle
Entire table structure must not tip under any operating condition
Must have an emergency stop fail-safe for control system
Must be able to withstand small movements from vehicle
Max weight of table should not exceed 500lbs; each individual piece should not
exceed 100lbs
Lift 1000 lbs. at least 60 degrees
Top-level Final Design Alternatives:
In the design phase, the team brainstormed concepts based on the constraints
detailed in the PDS. Initial brainstorming yielded a few designs; the team narrowed the
ideas down to few concepts, which can be seen in Appendix C. After utilizing a design
matrix shown in Table x in the Appendix C, it was decided the basis of our design shall
continue with the “Jack Table”. However, the next design phase was to determine the
process in which to power the table.
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A similar process was used in order to determine what type of system would power
the table and car to 60 degrees. There were multiple ideas which can be found within the
appendix. The design that won in the end was a power screw mechanism. This allows for
an easy safe way in order to lift the desired weight and is much cheaper than some of the
other methods.
Due to the basic design, it was decided as a team to redesign the table with a power
screw in mind. The team decided the simplest and most efficient system that provided the
essential force was to make a base consisting of two parts. This system provides the user
with an ease of use, safe, and reliable method to measure the center of gravity of the VMS
vehicle.
Final Design
Overview
Figure 1: Initial design concept which allows for the most accurate measurement of center of gravity.
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The complete design will be covered briefly; a more detailed description of each
component will be discussed in the following sections. The complete design is rather
simple, consisting of 3 main sections. The sections include the top, a base which is split into
two parts, and power screw system. A complete assembly is shown in Figure 2. The power
screw pushes the top part of the table along a fixed path. When lifted, the arms initially
resist the force applied by the power screw, but shortly after they travel with the top piece
of the table. A motor was used in order to provide the torque required to turn the screw
which causes the table to lift. Figure 4, shows the attachment between the power screw
and the table. The design is split into three groups, base, top and power mechanism. After
building the actual design, it was determined that the power screw did not function as
intended. A winch was used in its place. Both designs will be covered since the winch was
used only after the power screw failed. Technical drawings of the table can be found within
the appendix.
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Figure 2: Full assembly design concept (SolidWorks). The design shows the table tilted to 60 degrees
Figure 3: Actual assembly of the table.
Base Design
The lower structure of the assembly was initially modeled to be one large part.
Because of the loads present in the base, it was bulky and overweight to meet PDS
requirements. There was also an issue with the power screw being perfectly aligned
through the structure. Because of these concerns, the base was split into two separate parts
with the power screw running between the parts which can be seen in Figure 4. The
reasoning behind this was to provide the maximum support while making the
manufacturing processes simpler. There pieces that are attached between the two parts of
the base are only attached with bolts which can be taken out before the table is moved.
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Figure 4: Final design of the base with power screw.
The base is also designed to allow the rollers for the table to slide along a fixed path,
it was later determined that rollers were not needed in order for the table to function
properly. Initially, the idea was to have the rollers simply slide along the ground surface,
but it is likely that when the table is being used outside the surface will not remain level
throughout the length of travel. This change in design was made in order for the table to
work on any environment. In order to increase the length of the arms legs were added
underneath the base. These legs were designed in order to have the arms at a lower than
the table which helps with the initial force required in order to lift the table. This force was
determined to be the largest force and the change in design was the only possible way to
decrease the force required while keeping the same power mechanism.
Top Design
The top level of the design features a simple surface that holds the car in place. The
design also incorporates a tie down strap which is used as a safety feature when measuring the
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center of gravity. The strap prevents the car from falling off of the table once the angle is
increased to the tipping point. This strap is mounted to the top in order to maintain a constant
length along the rotation. If the strap was mounted to the bottom then the strap would need to
have an increasing length which would be proportional to the increasing angle. Figure 5 also
below shows underneath the top design and how the top is connected to the base. The figure
also shows how the winch is used which replaced the power screw in the final design.
Figure 5: Top of table with connections to base.
The top was also mounted to the power screw through the use of three supports.
The supports were initially more complex and required different material for construction.
Due to time constrains, the same material used in the top and base was used in the
assembly of the attachments. This attachment was removed after it was determined that
the power screw purchased was not capable of handling the load it received while lifting
the table.
Screw Design
The screw mechanism and its components were the most challenging part of the
overall design process. The screw required multiple parts to be machined on a mill which
took longer than expected. These parts are unique and critical to the overall function of the
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screw. The support which attaches the screw to the top of the table along with the bearing
which is required for the screw to produce force is shown in Figure 6 below. Figure 7
shows the motor which is attached to the end of the power screw in order to provide the
torque required to turn the screw. The bearing is welded onto a plate which is then bolted
onto the base. This design was done so that the base can still be separated into two
different parts.
Figure 6: Power screw with attachment to top and bearing attached to the base.
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Figure 7: Motor that turns the screw.
The screw was also required to push a force much larger than the 2,000 lbs. which
was initially estimated in order to lift the table. This increase in force is due to overcoming
the initial forces that come from the overall design. Because of this, the screw and its
components were designed with a force of around 8,000 lbs. in mind. The calculations for
the power screw can be found in the Appendix. What was not expected was that the screw
itself would buckle when turned by the motor which was attached to the table/screw.
Because of this failure, a winch was purchased in order to replace the initial screw design.
Some of the components that were associated with the screw were removed in order to
make room for the new design which can be seen in Figure 5 above. This winch provides
much more force than the power screw and it simple to swap one out for the other. The
winch provides the force required in order lifting the table, but it was also found that the
table starts to defect initially because of the large force applied. A photo of the table with
the winch can be seen in Figure
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Product Design Specification Evaluation
The prototype was evaluated using the PDS requirements. The main requirements
are listed in Table 1. All requirements were met with the exception of one, lifting 2000 lbs.
to at least 60 degrees, which was the most important design requirement. There are
multiple reasons why this did not work which will be further discussed in the conclusion.
Design EvaluationRequirements Importance Metric Target Verification AccomplishedFit into 6’ x 8’ trailer
**** Inspection Yes
Moved/Assembled by 2 people
**** Yes/no Yes Analysis/Testing Yes
Safety Tether ***** Yes/no Yes Inspection YesOperate inside/Outside
*** Yes/no Yes Testing Yes
Max weight> 500lbs
**** Lbs 500 Measurement Yes
Each piece > 100lbs
*** Lbs 500 Measurement Yes
Lift 2000lbs at least 60 degrees
***** Lbs/Degrees 2000, 600
Measurement NO
Table 1: Design Evaluation of VMS Tilt Table
Overall the main requirements that were outlined in the PDS were met. We felt that
this made the design process much easier. The PDS requirements are met only through the
continual modification of the design. The initial design did not meet many of the main
requirements once testing occurred. After redesign early on, the issues were fixed because
the PDS requirements were critical for the actual table to function properly. The table can
easily be reinforced in order to meet the requirement of 2000 lbs., but due to time
constraints, we were not able to provide the support needed for this force.
Conclusion
Overall, the capstone project was a success because all of the members of this team
have learned from the design process. Through continual modification of the design, we
were able to build a full tilt table that nearly met all of our design specifications. This table
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also cost substantially less than any other table that is on the market. The two main issues
with the design in the end were the power mechanism and the overall structure of the
table. The power mechanism was not able to resist the forces that were present in the
screw which caused the power mechanism to be replaced after it was fully assembled. The
winch that replaced the power screw is capable of providing the forces needed to lift the
car, but the actual table starts to buckle under the forces that are present. The table could
be easily reinforced in order to increase the overall strength, but it is likely that with
reinforcement, the table will be too heavy for two people to move on their own.
We as a team, and as prospective engineers, are very proud of this project and
prototype. Together, we faced many trials that we overcame through great problem
solving and team work. We hope this prototype will provide VMS with the building blocks
to design a better car for competition in the coming years.
Special Thanks
The VMS tilt table team would like to give special thanks to VMS and PSU’s
Mechanical Engineering faculty, specifically Dr. Wern, for his support in this project.
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Appendices
Table 2: Full Detailed PDS criteria:
Appendix A ●●● - High Priority ●● - Medium Priority ●- Low Priority
Priority
Requirement Customer
Metric Target Target Basis
Verification
Performance●●● Operate with
1000lb load (car and driver)
VMS Pounds Force 1000 Physics Prototyping
●●● Tilt the vehicle 60 degrees
VMS Degrees from horizontal
60 Physics Prototyping
●● Tilt the vehicle 70 degrees
VMS Degrees from horizontal
70 Prototyping
●● Control of inclination rate
VMS Degrees per second
-
●●Ability to level VMS Degrees from
horizontal+ or – 0.5 degrees
●● Powered by 12v battery
VMS - Yes
●●● Mobile VMS Yes Prototyping
Environment●●● Operate indoors
and outdoorsVMS - VMS
Requirement
Design
●● Life In Service VMS Cycles 3 Future Use Design
●●● Cost Of Production Self $ < 1000 Budget Design
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Size and Shape●● Volume VMS / Self ft^2 < 40 Ergonomics
/ Ease of transport
Prototyping
●● Weight VMS / Self lbs < 200 Ergonomics / Ease of transport
Prototyping
Maintenance●● Accessibility To
ComponentsSelf Number of
people required1 Ease of
maintenance
Prototyping
●● Availability Of Replacement Parts
Self Days required for arrival
< 6 Timeline Prototyping
●● Tool Requirements Self Availability of tools required to
maintain
All in lab Ease of maintenanc
e & operation
Prototyping
Ergonomics●● Ease Of Use Self Number of
people required to operate
2 Expert opinion
Prototyping
Safety●●● Structural Integrity VMS VMS
Requirement
Inspection
●●● Ergonomic Safety VMS yes / no All edges padded / secured
VMS Requiremen
t
Prototyping
Materials●● Structure Self yes/no Simple to Expert Prototyping
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build opinion
●● Aesthetics Self yes / no Looks sturdy &professiona
l
Self interest First hand
Appendix B: External Research Summary
Efficient and balanced use of the external search process resulted in the realization
by the design team that the project needed to be divided into two sub categories for
research. The first research category was based on the overall table design concept, while
the second category focused on the internal actuation mechanism of the table. Broadly
gathering information on available tilt table designs using open source research methods
led to discovery of a wide range of tilt-table designs. The most commonly used style of table
for formula SAE vehicles consists of an L-shaped table driven in a swing configuration by
hydraulic actuators Fig. B1.
Figure B1 – Hydraulically Actuated Tilt Table Figure B2 – Collapsing Edge Pivot Table
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While this design passes the majority of the teams PDS requirements, it fails in the
critical area of mobility. The second design in Fig. B2 was designed as a collapsing table
over a baseplate with a fixed pivot point along one side. The primary flaw in this design is
the fixed pivot point, which causes the table to become increasingly unstable as it increases
in angle. Ultimately, this design served as the benchmark design moving forward in the
design process. A third table type was also considered, as shown in Fig. B3. While
innovative in its use of human power to control the tilt of the table, it would be difficult to
move, and would not be operable in an indoor environment after set up.
Figure B3 – Human Powered Tilt-Table Design
External searches for actuation systems resulted in a wide range of designs and
mechanisms which could be used in the final table design. While not a comprehensive list,
some of the devices researched were: cable winches, power screws, hydraulic actuators,
linear actuators, counterweights, and pneumatics.
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Appendix C: Top Level Alternatives
Consistent with the external search process, the internal search was divided into
two sub categories. After brainstorming and presentation of ideas by team members,
decision matrices were developed and used to analyze the conceptual designs against the
PDS requirements. Criterion considered and evaluated for the internal actuation
mechanism were: lift capacity, overall weight, cost, ability to control rate, and power
source. After unbiased debate and analysis, items were scored against each other resulting
in decision matrix shown in Table C1.
RequirementCapacity Weight Cost Rate
ControlPower Source
Total
Actuator
Wench 5 3 2 6 2 18
Power Screw 2 1 3 1 3 10Hydraulic 1 5 5 4 5 20
Counterweight 6 6 1 5 1 19Pneumatic 4 4 4 3 4 19
Linear Actuator
3 2 6 2 6 19
Table C1 – Actuation System Design Matrix
The second stage of the internal search consisted of presentation and analysis of
conceptual table designs. Team members each designed their own concept for the overall
design and presented them during the weekly capstone meeting. A design matrix was
developed, and designs were scored on a scale of 1-5, where 5 is the highest value. To avoid
a tie, categories of analysis were weighted by importance. The result is in Table C1.
Storability (1)
Mobility (5)
Cost (2)
Weight (3)
Assembly Time (4)
Stability (6)
Final Score
Modular
4 15 8 12 16 24 79
Tall 4 20 8 13.5 16 24 85.5
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Winch 3 15 8 9 20 18 73Jack 3.5 20 8 12 20 30 93.5
Swoosh 4 15 7 13.5 8 30 77.5Table C2 – Table Concept Design Matrix
The final weighted score determined that the overall design would be a collapsing
tilt-table actuated by a power screw based scissor-jack which is built horizontally into the
base of the table. In appearance, the table would be similar to the externally researched
table used as the benchmark design. The primary modification, outside of the actuation
system, is that the pivot point will translate through the table as it tilts, increasing the
stability of the table by keeping the center of gravity centrally located.
Design matrix (Table C2) Shows That both the tall table and the modular table are
also viable solutions, the jack table happened to have the best overall design, but the tall
table as well as the modular table offer aspects of stability and actuation, which is why we
plan to incorporate the best aspects of these designs in our final design.
Modular Table:
The modular table is a good option because it incorporates the fewest parts, and
therefore would have a fairly simple fabrication. we named it the "Modular Table because
to stay within the weight parameters of the PDS we would have to manufacture the table
with several removable (modular pieces) the main drawback to this design is the fact that
is has a fixed pivot point shown in (Figure C1). With a fixed pivot the center of gravity of
the system would shift during lifting, which would require us to have a base with a larger
footprint, and that would detract from the storage and mobility aspects of the PDS.
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Figure C1: Tilt table featuring a fixed pivot point
Tall Table:
The tall table was named that because unlike all the other tables it featured an
adjustable base height, which could potentially allow for the table to double as a
maintenance platform as well as a tilt table. The adjustable legs would also feature an
insert which would allow for casters to be inserted see figure C2. with the ability to insert
casters the table is a good design for the increase in mobility, however it does loose some
points in stability, as the higher we raise the center of mass from the ground the more
unstable our design becomes and as shown in the PDS Table 1 stability is the most
important aspect of our design.
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Figure C2: table leg featuring caster option
For the purpose of increased mobility casters are planned to be placed on the final
tilt table design.
Appendix D: Finite Element Analysis
Finite element analysis was used in order to determine the forces that are present in
the critical components of the table. The top part of table was modeled in FEA in order to
determine the deflection that occurs. This model can be seen in figure D1 below. The two
locations with the largest stresses were determined to be the arm and the bolt which
connect the top part of the table to the base. These locations still had a factor of safety of
1.17 for the arm and 2.13 for the bolt. The FEA of both of these members can be seen in
figure D2 below.
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Figure D1: FEA of top of table.
Figure D2: FEA of arm and bolt. (Factor of safety of 1.17 and 2.13 respectively)
Appendix E: Technical Drawings
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Two technical drawings of the table are shown below in Figure E1 and E2. These
two drawings show the table when it is lying flat as well as showing the table when it is at
60 degrees.
Figure E1: Technical drawing of table lying flat.
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Figure E2: Technical drawing of table at 60 degrees.
Appendix F: Hand Calculations of Forces
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