1

Team PATS Phase 4

Sponsor: PATS Aircraft

Contact: Matthew Porter

Team Members:

Mike Brody Phil Holcombe

Adam Konneker Nick LaRocca

Claire Ngengwe

Advisor: Dr. Hartman

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Table of Contents

Executive Summary……………………………………………………………………………….3

Background Information…………………………………………………………………………..3

Current Process……………………………………………………………………………………3

Wants and Constraints…………………………………………………………………………….4

Design Concepts

Initial Concepts……………………………………………………………………………4

Final Concept……………………………………………………………………………...5

Prototype…………………………………………………………………………………………..7

Testing and Validation

Critical Performance Goals………………………………………………………………..8

Performance Goals Evaluation……………………………………………………………8

Result and Discussion……………………………………………………………………..9

Implementation…………………………………………………………………………………..10

Cost Analysis…………………………………………………………………………………….11

Conclusion……………………………………………………………………………………….12

Appendices

Appendix A………………………………………………………………………………13

Appendix B: Testing and Analysis.…………………………………………………...…15

Appendix C: Bill of Materials……………………………………………...………….…23

Appendix D: Full Scale Design……………………………………………………….…27

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Executive Summary PATS Aircrafts, a subsidiary of DeCrane Aerospace, is an aerospace company that

develops and manufactures specialized aircraft systems. Primarily, they make several different

auxiliary fuel tanks for multiple types of aircraft. Roughly 80% of the tanks manufactured by

PATS are for the BBJ (Boeing 737 Business Jet) and the Boeing 757. PATS Aircrafts presented

our senior design team with the challenge of improving their manufacturing process for their

auxiliary fuel tanks.

Currently, the tank manufacturing process is primarily manual labor from start to finish.

The tanks are lifted manually from one table to another as they go from station to station

throughout assembly and into painting. Once the outer shell of the tank is assembled it has to be

moved and rotated a number of times in order to install inner components. The moving process

can take at least three people to perform and during this process the tanks are more susceptible to

damage from scratches or dents and this process can also lead to worker injury.

In an effort to move towards lean manufacturing, PATS Aircraft wants a device that can

support and rotate these tanks throughout the assembly process. PATS also wishes to reduce the

time in which it takes to manufacture the tank and to reduce any potential risk of injury to

workers. The main purpose of this project is to design a device that can support and rotate a tank

during the manufacturing process. This apparatus will cut down the time a tank is in the

assembly process. It will also cut down on labor time lost from workers having to stop to help

move or rotate a tank and reduce risk of injury to workers.

Background Information PATS Aircrafts, a subsidiary of DeCrane Aerospace, is an aerospace company that

develops and manufactures specialized aircraft systems. Primarily, they make several different

auxiliary fuel tanks for multiple types of aircraft. Roughly 80% of the tanks manufactured by

PATS are for the BBJ (Boeing 737 Business Jet) and the Boeing 757. PATS Aircrafts’ goal for

this project is to substantiate improvements to their current design for their auxiliary fuel tanks.

These improvements can include structural integrity, system weight, fuel transfer performance,

tank maintainability, manufacturing processes, and repair procedures or material selection. After

communicating with the sponsor, the scope of the project was defined to specifically tackle the

manufacturing process.

Current Process Currently, the tank manufacturing process is primarily all manual labor from start to

finish. The tanks are lifted manually from table to table during most steps of the assembly and

painting process. Once the outer shell is assembled it has to be rotated and moved several times

for installing inner components and painting. Moving takes at least three people to perform. The

tanks can also be damaged during this process and it can also lead to worker injury. In an effort

to move towards lean manufacturing, PATS Aircraft wants a device that can support and rotate

these tanks throughout the assembly process. They also wish to reduce the time in which it takes

to manufacture the tank and to reduce the risk of injury to workers.

The main purpose of this project is to design a device that can support and rotate a tank

during the manufacturing process. This device will cut down the time a tank is in the assembly

process. It will also cut down on labor time lost from workers having to stop to help move or

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rotate a tank and reduce risk of injury to workers. This device should reduce the chance a tank

will be damaged during the assembly process.

Wants and Constraints For this project, our only customer is PATS Aircraft. Our design concept will be

governed by PATS Aircraft wants and constraints along with associated metric values. They are

as follows:

Constraints

1. Hold one BBJ (Boeing 737 Business Jet) auxiliary fuel tank (size and weight) plus two

workers and equipment

2. Rotate tank through 360-degrees on one axis

3. Raise and lower tank 48 inches.

4. As safe as (or safer than) current process to tank and workers

Wants

1. Cheap enough for small-scale production

2. Adjustable height

3. Lockable rotating assembly

4. No larger than tables currently in use

5. Able to move throughout factory freely

6. Simple

7. Customizable for different tank models

8. Operable by two (or less) workers

9. Fit inside paint booth/functional for paint booth

Design Concepts Initial Concepts

After extensive benchmarking of relevant technology

to our application, we began to formulate concepts.

Using the wants and constraints our team came up

with several concepts for a solution to the problem

definition. Our main concept for holding the BBJ

tank was a metal frame shaped similar to an

automobile rotisserie. This frame should be able to

lift and rotate the tank using two concentric tubes that rotate and a pin to lock it at different

angles. The frame could be made out of several materials, of which aluminum and steel are the

top two materials considered. Both materials have their advantages and trade-offs in terms of

cost and weight.

For the lifting mechanisms, our group found numerous

systems that would work well for our purpose. Two of them

were a screw lift that was powered by an electric motor and a

hydraulic lifting system. The hydraulic system would have to be

large and heavy to give us the stroke length we want and would

not be very cost effective, and the screw jack would be too

heavy to provide the desired stroke length. We came up with

Figure 1

Figure 2

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several concept designs that utilize a pulley system (Figure 2). The pulley system can be

powered by an electric motor or a manual hand crank.

There were also several different systems that we came up with that

could hold the tank in place on the frame. One idea was to have a rail with

toggle clamps (Figure 5) that can be attached to the support rail that already

exists on the side of BBJ auxiliary fuel tanks. The rails are a good place to

attach to because they are made to withstand a 9-G force which is far more

than it would ever experience while being fabricated. Our contacts at PATS

wanted us to move away from toggle clamps because they feared that they

would not be secure enough to hold the tank while the rail was at a 90

degree angle. Another reason is that the toggle clamps may dislodge by

someone passing by. Another idea was to have suction cups powered by a

vacuum. This concept would utilize the smooth surface of the tank to attach to. This idea is

superior for handling delicate objects such as the honeycomb aluminum and is also highly

adaptable to different size parts. Some drawbacks are that it has to be continuously powered

while the tank is in the air, the system is expensive and there is high maintenance associated with

it. An additional idea was to create a steel locking mechanism to hold on to the rails. The

clamping mechanism would be bolted to the rails on the side of the fuel tank. To prevent metal

on metal contact the clamp would be lined with polyethylene. Now all these concepts we

generated need to be evaluated based on how well they fulfill the customers wants and

expectations.

Final Concept

First, we determined if the concepts satisfied

the customer’s constraints. If the particular concept

does not meet these requirements, it can be

automatically thrown out. Once this is done, we have

solid concepts that will satisfy the goal of the project.

Now the concepts need to be evaluated to see how

well they meet the wants of the customer, and

whichever concept satisfies these wants the best will

be used for the final design. To do this

quantitatively, we developed a spreadsheet to rate the

concepts we came up with earlier in concept

generation (Concept Selection: Appendix A). With

collaboration from the sponsor, the wants were ranked

and weighted based on their importance to the project. With this information, metrics along

with target values were formulated. These were also given values of importance based on the

wants they satisfy. All the concepts were rated on how well they fulfill these metrics. They

were given either a 1 for doing well they do against the target values of the metric, 0.2 for being

average or -1 for doing poorly. 0 is awarded if the metric does not apply or is unknown.

Figure 3

Figure 4

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Metrics Target Values

Weighted

Importance Aluminum Steel Suction Cup Toggle Clamps Screw Jacks

Manual Pulley

System

Electric

Pulley

Hydraulic

Lift

Reliability >99% 100 1 1 1 1 1 1 1 1

Cost <8000 USD 90 0.2 1 0.2 1 -1 1 1 0.2

Dimensions ≤ 8 x 4 x 6 ft (l x w x h) 85 1 1 1 1 1 1 1 1

System Weight < 500 Lbs 75 1 -1 1 1 0.2 1 0.2 0.2

Adaptability # of Tanks ≥ 1 50 0.2 0.2 1 0.2 1 1 1 1

Maintenance Minimal 40 1 1 0.2 1 0.2 1 0.2 0.2

Lifting Speed ≤ 1 min. 40 0 0 0 0 -1 0.2 1 1

Ease of Use Simple Controls 35 1 1 0.2 1 1 0.2 1 1

Automation Low manual operations 30 1 1 1 -1 1 -1 1 1

Degrees of Freedom ≥ 1 DOF 10 1 1 1 1 1 1 1 1

Required Personnel ≤ 2 Workers 10 1 1 1 1 1 1 1 1

Total Score 413 335 393 425 213 445 473 401

Good 1

Average 0.2

Poor -1

Unknown 0

Frame Material Tank Clamping Systems Lifting Mechanism

Metric Performance Rating

Table 1

The concepts that performed well in this evaluation will be

utilized in our final concept design. For the frame material, steel

performed the best. This is due to its strength compared to

aluminum and because it cost less than aluminum. A custom

made steel clamp mechanism will be used to secure the tank's rail

to the frame that rotates the tank. These were chosen because they

are made specifically for this task. Lifting mechanisms consumed

most of the deliberation we had into determining a final concept.

After we narrowed it down to four concepts and evaluated them,

an electric/manual pulley system performed the best. It's relatively low cost and ease of use

made it an optimal choice for vertically lifting the tank during the manufacturing process. All

these subcomponents will be combined to form the final concept of our BBJ fuel tank rotisserie.

Our concept incorporates what we feel to be our "best" ideas for the various aspects of our design

criteria. First, our frame will be made of square steel tubing. Square tubing is relatively cheap,

and easy to join together using bolts and simple-geometry brackets. These bolts and brackets

will also make the frame easy to disassemble for maintenance, cleaning, moving, and storage. If

a single piece breaks, a bolted joint is much easier to disassemble than a welded joint. To aid in

this maneuverability, our frame will also be on locking casters. Our choice in lifting

mechanisms is an electric cable and pulley system. This design provides the greatest ease-of-use

with few parts, and a good reliability. To raise and lower the tank, a

worker needs only to press a single button to start the electric winch.

Once the tank is in the desired position, releasing the button stops the

tank, and locks it at that height due to the self-locking winch. An

electric winch eliminates workers having to physically lift the tank.

In addition, should a component of the system fail, replacing it is a

quick, low-cost task – save the electric winch in comparison this to a

screw jack system. If any one component fails, the cost to replace that

part should be fairly minimal. If a pulley fails, it cost very littler to buy

a new one, and the system is fully operational again.

To rotate the tank, we have a grip comprising of clamps and a

rotating-sleeve pivot. The clamps are offset from the axis of rotation

to allow the tank to rotate around its center of gravity. This makes

rotating the tank easier for the operators because there will not be a

large moment trying to spin the tank to its “neutral” position. The

Figure 5

Figure 6

Figure 7

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clamps will attach to the tank by means of existing support rails. These rails are designed to

support the tank - full of fuel - against a 9-G lateral force, and, therefore, are more than adequate

to support the weight of an empty tank and two workers. The pivot will be a simple dual-

cylinder joint, where one cylinder rotates freely inside of another, larger cylinder. To stop the

tank from rotating on its own, the inner cylinder will have a series of holes drilled around the

circumference. The outer sleeve will have one hole with a spring pin in it. When the tank is in

the desired orientation, the pin will slide into the corresponding hole in the inner cylinder,

therefore, locking the tank in that position. Each inner sleeve will

have a large hand wheel attached to the outside to give the

operators a strong grip to spin the tank to the necessary angle.

Inside frame will be a removable tabletop. This will allow

an operator to reach the upper parts of the tank while it is raised,

and another operator is working in the tank from the floor. This

raised platform will take the place of the wooden tables currently

in use during the production process, and help head towards “lean

manufacturing”.

Prototype

The prototype needs to demonstrate the lifting,

clamping and rotating mechanism of our design. We need a

lifting system that can achieve the required stroke length of

4 feet and still meet our metrics values. We will be using a

pulley system with a manual winch to accomplish this goal.

The system will also be designed so the manual winch can

be switched out for an electric winch. The performance of

the pulley’s need to confirm how safe and stable it would be

to lift the tank without damage. The ergonomics of our

design will also be tested.

The prototype needs to verify the rotating system

can rotate the tank using a manual hand-wheel with relative

ease. The ease will depend on the tanks weight and the

friction on the concentric tubes used for rotation. The prototype needs to show that the tanks

center of gravity is located on or about the axis of rotation. The rotational locking system will be

tested to make sure it restricts rotational motion while in locked position. The removable

working platforms will not be constructed as part of the prototype because no testing is required

to verify their design.

The clamping system is the same as our final design because it is a crucial component.

This is the only thing touching the tank and keeping it from falling to the ground. I will be

welded steel with polyethylene contacts. We will be using half inch bolts to secure the clamps

on the tank rail as well. The frame of our prototype is quite different than the frame of our actual

design. Since, we needed to make a full-scale prototype we had to somehow reduce the cost.

We simplified the design of the frame and changed the material to cut down on material costs.

Figure 11: Prototype Frame

Figure 8

Figure 9

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The material we are now using is still steel, but we are using 2 inch square bar instead of 3 inch.

This allowed us to make the frame out of less material.

Testing and Validation Critical Performance Goals for Proof-of-Concept Prototype

Several critical performance goals were developed to determine the validity of the prototype.

Our prototype must meet these requirements in order to validate our concept. One major goal

that encompasses everything on our prototype is safety. There are many other goals that need to

be validated as well. These goals are outlined below:

• Steel Frame Subsystem

o Validate Design

o Minimize Deflection (Less that 1/2"

on uprights)

• Lifting Subsystem

o Lift and lower BBJ tank 4 feet

o Adequate winch ergonomics

• Rotation Subsystem

o Rotates tank manually 360°

o Verify location of tank center of

gravity

o Clamps securely hold tank with people

inside at different tank angles

o Locking system works properly

One performance goal for the prototype is to support a BBJ tank safely and without

significant deflection. Significant deflection will be quantified as more than 1/2" at the top of the

uprights laterally. This is important because deflecting inwards would create a compression

force on the tank which could result in tank damage.

Another performance goal for our prototype

is to validate the lifting mechanism of our design.

The combination of our lift and rotation system is an

original design and needs to be verified by testing.

Its performance needs to confirm that it is indeed

safe and stable enough to lift the tank without

damaging it as well as its ergonomics since it is a

manual system.

Finally, probably the most critical

performance goal is for the rotation system itself.

We need to verify that the tank can be rotated from a

manual hand-wheel with relative ease. This depends

on the tanks weight and friction on the concentric

tubes that are used to rotate the mechanism. It needs to show that the tank easily rotates about its

center of gravity. It also has to show that our design is robust enough to support the tank and

workers that will be moving around in the tank. The locking system should also perform as it is

Figure 10

Figure 11

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supposed and prevent motion while in the locked position. We will not be constructing the

removable working platforms. These are not necessary to demonstrate the other performance

goals, and there is no new technology associated with them.

Performance Goal Evaluation

Evaluating our design is the most important part of Phase 4. The most important testing

will be done on the system as a whole. The BBJ tank will be loaded on frame and clamped into

place. Additional weight will be added to represent the weight of two workers. We established

this to be 400 pounds. The main objective is to replicate actual loads that the frame will

experience, and determine if any parts will fail during operation. Once the tank is locked in

place, the tank will be lifted into the air using the manual winches on the prototype. After the

tank reaches the top, it will be rotated one revolution and then lowered back to the original

position. This test will be repeated 50 times. We will

measure the number of failures that occur during these

cycles. A failure can be any number of things from the

rotation system or lifting system locking up or the clamp

system releasing unexpectedly. We are looking for over a

99% reliability rate, but over 95% would be acceptable for

the initial part of the testing phase. If the prototype passes

this test then it would validate the lifting and rotating

mechanism.

The lateral deflection in the uprights of the frame

will be measured also. This is important because a large

deflection could possibly damage the tank by putting

compressive forces on it. An acceptable deflection will be

less than half an inch. This will be quantified by measuring

the distance between uprights when the prototype is loaded

and unloaded and the taking the difference between the

two. This will be down ten times and the average will be

taken.

Another goal is proper ergonomics. This will be accomplished by analyzing the sequence

of lifting and lowering and seeing if can be done easily by two operators. The hand wheel on the

rotation subsystem and the crank on the winch will be evaluated the most rigorously. The hand

wheel ergonomics will be determined by seeing if two average people can turn the hand wheel.

If they can operate it with ease then our prototype will satisfy this test. When determining

whether or not this is acceptable, we have to account for the range physical abilities of people

that will possibly have to operate the system.

Our calculation for the center of gravity will need to be verified by loading the system

with a tank and observing the tank while it is being rotated. If the operator loses control and the

tank turns unassisted, that means our calculations were wrong, and the design needs to be

adjusted. This also will help determine the safety of the system. The possible pinch points will

also need to be analyzed for this subsystem. Analysis of structural integrity of clamp-base has

been done using STAAD.pro and can be seen in Appendix B (Figure 2).

Figure 12

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Results and Discussion

The first test that was run was the lifting, rotating and lowering of the tank using the

prototype. The results of this test are as follows:

Cycles Failures Reliability

50 1 98% Table 2

The reasons for failure during this test were determined to be caused once by uneven

lifting of the tank. This was the result of one winch lifting the tank faster than the other winch

which caused the sliders on the uprights to lock up.

The next test performed was the deflection in

the uprights (Table 3). The average deflection was

determined to be .153 inches which was well within

our predetermined performance goal. The max

deflection we found was under a quarter inch as well.

Our prototype did well on this test.

The final part is determining the torque

required to turn the hand wheel that turns the tank and

the crank for the winch. The force on the hand crank

was determined analytically using the dimensions of

the winch, the weight of the tank, and the gear

reduction of the winch. This was found to be 1.32 lbf. Friction in the gears and pulleys was

neglected. We found the force to be much higher during testing. It could be turned with relative

ease, but the force was higher and the number of turns was 40 for one revolution. This caused

fatigue to be an issue.

The torque required to rotate the tank was unacceptable. The pivot was not around the

center of gravity and the overturning moment was larger than operators can overcome. This was

due to not accounting for the weight of the clamps as well as the tank in the calculations for

center of gravity. This can be fixed by cutting the welds and welding the pivot point closer to the

clamps. Also, this can be improved by adding a lubricant to the rotation mechanism. It could

also be improved if two people are operating the hand wheels, one on each side.

Now, in terms of safety our prototype was observed thoroughly. There could be pinch

points on the pulleys at the bottom of the frame on both sides if someone gets to close during

raising and lowering. This could be eliminated by placing covers over the pulleys. In

conclusion, all ergonomics were determined to be acceptable and not cause repetitive stress

injuries. Other than that, the system will operate safely as

long as people stay clear while lifting and lowering.

Instructing workers to stay clear will be part of our

implementation plan.

Implementation In order to move our design into a working item

that can be used on the tank shop floor at PATS aircraft

there are a few steps that need to be undertaken. At this

point the final design is completed. To fully implement our

Figure 13

Figure 14

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design into PATS, first the fuel tank rotisserie will need to be built. The parts required will be

ordered. Once those parts arrive, they will be machined and then assembled. Since the number of

units is fairly small, no mass production methods should be implemented. The process will be

very similar to the one that we used to construct the prototype. Then the design will be

implemented into the manufacturing process. This process requires training the workers how to

use the mechanism properly as well as safety measures that should be taken. We can remove the

old tables that are currently in the factory, since our rotisserie will eliminate the need for this.

The rotisserie can be used from the instant the outer shell is assembled up until the tank is

finished being painted. During painting, the rotation and pulley system should be covered to

prevent paint from getting on it.

Cost Analysis The prices for the components are given from McMaster-Carr. The total costs for our

subsystems for the prototype and final design are listed below in Table 1 and Table 2

respectively. For a breakdown of all individual components and estimated costs see Appendix C.

Factors that went into pricing our components were load ratings, material, part dimensions and

shipping. For example, electric winches come in various sizes and types, all with different

capabilities depending on load and load orientation. We needed an electric winch that could lift

a certain load in the vertical direction. Other winches were designed specifically for horizontal

or inclined motion. When pricing pulleys we had to account for load, rope diameter and

minimum radius that the rope could be bent into. For the components of the frame, such as steel

tubing, casters, nuts and bolts, the main factor in cost was load rating because these are the parts

that will be taking the load of the whole system. Also, there are many shapes and sizes for steel

tubing, but we needed to make sure that the dimensions that we used would suffice as cost can

easily increase with size. The work tables will be neglected in the prototype so they are not

included in the cost estimate.

Subsystem Total Cost Est.

Steel Frame 1250.00

Lifting System 111.00

Rotating System 969.00

Engineering 0.00

Testing 0.00

Total 2330.00

Subsystem Total Cost Est.

Steel Frame 1576.00

Lifting System 111.00

Rotating System 969.00

Contingency 532.00

Engineering 0.00

Testing 0.00

Total 3188.00

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Conclusion

Our prototype proved to be very successful. It fully demonstrated that our concept will work as

it should. The lifting mechanism worked well although we would make minor changes to the

final design. The manual winches took too long to raise the tank. Sometimes up to 3-4 minutes.

Electric winches would speed this up drastically as well as minimize the effort required by the

operators. The rotating mechanism proved our concept, but the location of the center of gravity

was off. This was accounted for in our final design that will be implemented at PATS Aircraft.

Also, 3 inch steel tubing will be used for the frame instead of 2 inch. The frame did not deflect

too much, but it will need to be more rigid when operators our on the tank. This is just a safety

precaution. The clamping system was a great success. It held the tank in place will it rotated

upside down all while not damaging the tank. This will be identical to what is implemented at

the sponsor. The nylon casters lock well, but they can slip along the floor even when loaded by

the tank. For this reason, floor locks will be required when being used by the sponsor. Other

than these minor changes, our prototype fully demonstrated our concept. The tank could be

lifted three feet. It can be rotated one revolution. The tank is securely locked in the clamps.

This design is safer than the current process because it takes the tanks weight off the operators to

move it. Our device will be a great benefit to our sponsor.

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Appendices

Appendix A:

Constraints 1. Hold one BBJ (Boeing 737 Business Jet) auxiliary fuel tank (size and weight) plus two

workers and equipment

2. Rotate tank through 360‐degrees on one axis

3. Adjustable lower‐supports to take weight off of rotating assembly during tank fabrication

4. As safe as (or safer than) current process to tank and workers

Wants 1. Operable by two (or less) workers

2. Cheap enough for small‐scale production

3. Adjustable height

4. Lockable rotating assembly

5. No larger than tables currently in use

6. Able to move throughout factory freely (Lockable wheels)

7. Able to hold tank indefinitely with no outside input (user, electricity, air pressure, etc.)

8. Simple

9. No electrical power required

10. Customizable for different tank models

11. Counterbalance off‐center tank

12. Fit inside paint booth/functional for paint booth

Metrics

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Concept Selection

Metrics Target Values

Weighted

Importance Aluminum Steel Suction Cup Toggle Clamps Screw Jacks

Manual Pulley

System

Electric

Pulley

Hydraulic

Lift

Reliability >99% 100 1 1 1 1 1 1 1 1

Cost <8000 USD 90 0.2 1 0.2 1 -1 1 1 0.2

Dimensions ≤ 8 x 4 x 6 ft (l x w x h) 85 1 1 1 1 1 1 1 1

System Weight < 500 Lbs 75 1 -1 1 1 0.2 1 0.2 0.2

Adaptability # of Tanks ≥ 1 50 0.2 0.2 1 0.2 1 1 1 1

Maintenance Minimal 40 1 1 0.2 1 0.2 1 0.2 0.2

Lifting Speed ≤ 1 min. 40 0 0 0 0 -1 0.2 1 1

Ease of Use Simple Controls 35 1 1 0.2 1 1 0.2 1 1

Automation Low manual operations 30 1 1 1 -1 1 -1 1 1

Degrees of Freedom ≥ 1 DOF 10 1 1 1 1 1 1 1 1

Required Personnel ≤ 2 Workers 10 1 1 1 1 1 1 1 1

Total Score 413 335 393 425 213 445 473 401

Good 1

Average 0.2

Poor -1

Unknown 0

Frame Material Tank Clamping Systems Lifting Mechanism

Metric Performance Rating

Our first thought is about how to

hold and rotate a fuel tank.

An idea of how to raise and lower a

support table for working on the

tanks.

The rotating mechanism and a way to adjust the support table

Figure 11 Figure 10

Figure 12

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Appendix B: Testing and Analysis

Distance Between

Uprights

All

values in.

Unloaded Loaded Deflection

128.72 128.59 0.13

128.81 128.63 0.19

128.75 128.59 0.16

128.72 128.50 0.22

128.78 128.53 0.25

128.72 128.47 0.25

128.75 128.59 0.16

128.78 128.72 0.06

128.81 128.84 -0.03

Average 0.15

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Above (Right): Clamp-base load was applied as a 7lb-in distributed load across the top (weight

of tank) and a 250lb concentrated force (weight of person) on one end. (Left): deflection of

clamp-base

Above: displacements of nodes on clamp-base. All displacements are small and can be

considered negligible.

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Column Design

The column was first checked for buckling if the load was applied concentrically.

Calculated here are the radius of gyration, k, the slenderness ratio, S,, and the tangent point on

the Johnson/Euler diagram, (Sr)D. (Sr)D determines whether the column can be categorized as a

Johnson or Euler column. These values are all used to calculate the critical load per unit area

Pcr/A. Our slenderness ratio is to the left of the tangent point and the critical load per unit area is

less than the compressive yield strength which is taken as the tensile yield strength. The

compressive and tensile yield strengths are usually close and this approximation is considered

safe. Applying our points to the Johnson Euler diagram we see that we have a Johnson column

with a load in the safe region.

We have shown that our column can handle the load if loaded concentrically, but we have

an eccentrically loaded column. This eccentricity, er, is calculated in the Figure. The load is

eccentric in two directions and the column is being bent about a strange axis. The axis is rotated

an amount θ from the x-axis. Although the column is being bent about this axis it will not fail

about this axis. It will still buckle about the x-axis, but it will probably torque and rotate some

during buckling. A worse case scenario might be to apply the same load with the same resultant

eccentricity but bending about the x-axis. A similar analysis is performed as in the

concentrically loaded analysis, but the secant formula is used to fit the data to the Johnson/Euler

diagram. Also, an eccentricity ratio, Er, was calculated. The eccentricity ratio changes the shape

of the secant line. Our value of Er, was very hard to extrapolate on the diagram. Another

buckling check had to be performed. It is known that a column will buckle when the max

compressive stress at the middle exceeds the yield strength of the material. The max

compressive yield stress was then calculated and compared to the yield strength of the material.

It showed that our column would hold the load. The deflection at mid-span was also calculated

to be 1/37”. This should be almost unnoticeable and can be measured on the prototype.

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21

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Tipping analysis

One worry about our structure was the stability when the tank was suspended at max

height. We performed some stability calculations to check if the structure would tip with the

tank at max height and a person applying a load at the side when the casters are locked. The

force applied by a person was assumed to be the same as the force of a person leaning against a

wall. The force of a person leaning against a wall as a function of angle was plotted on Maple.

Next, this force was applied to the structure at the height of an average person, about 6’. We

found that the structure will not tip over. Two people may be able to accidentally lift one side

off the ground a small amount, but this will be noticeable before they completely tip the

structure. Also, the only reason for two people to apply considerable force to the tank would be

to move the structure. If the structure is to be moved the casters will be unlocked and the

structure will roll well before it tips. Also, the weight of the structure and tank has increased

significantly from design changes after prototyping. This increased weight directly increases the

force needed to tip the structure.

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Appendix C: Bill of Materials

Final Design Cost Estimate

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25

Prototype Cost Estimate

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Appendix D: Full Scale Design

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