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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