Team 15: Swayspension

Final Design Report

May 8, 2013

Meng Chen, ME

Scott Kamp, ME

Nate Konyndyk, ME

Jacob VandeHaar, ME

Engr339/340 Senior Design Project

Calvin College

© 2013, Team 15 and Calvin College

ii

Executive Summary

This report outlines and describes the design and fabrication of Team Swayspension’s Prototype. We

explore the many engineering and non-engineering aspects of starting and managing a sizable mechanical

project. Our project is to design and fabricate a concept vehicle which incorporates a new, leaning

suspension. This new suspension reduces lateral acceleration felt while cornering, increases vehicle

performance, and makes driving more dynamic and exciting. Our research shows that many similar

vehicles achieve tilting by using active hydraulic actuation, which limits the spontaneity of the leaning

action and puts additional parasitic losses on the engine. Instead, our design leans passively through the

use of inertia. The design and analysis presented in this report conclude that the project is feasible, and the

fabricated prototype supports our conclusion.

Table of Contents

Team 15: Swayspension ........................................................................................................................ i

© 2013, Team 15 and Calvin College ............................................................................................................... i

Executive Summary ................................................................................................................................ ii

Table of Figures ...................................................................................................................................... v

1 Introduction .................................................................................................................................... 1

1.1 Team Members ....................................................................................................................................... 1

1.2 Problem Statement .............................................................................................................................. 1

2 Design ................................................................................................................................................. 2

2.1 Design Norms ........................................................................................................................................ 2

2.2 Design Challenges ................................................................................................................................ 2

2.2.1 Simplicity ....................................................................................................................................................... 2

2.2.2 Manufacturing Capabilities..................................................................................................................... 3

2.2.3 Adjustability .................................................................................................................................................. 3

2.3 Individual Component Design ......................................................................................................... 3

2.3.1 Frame ............................................................................................................................................................... 3

2.3.2 Primary Suspension................................................................................................................................... 5

2.3.3 Secondary Suspension .............................................................................................................................. 9

Steering ............................................................................................................................................................................ 10

2.3.4 Powertrain ................................................................................................................................................... 12

3 Force Analysis............................................................................................................................... 13

3.1 Primary Lower Control Arm ......................................................................................................... 13

3.2 Connection Block............................................................................................................................... 14

3.3 Threaded Tie-Rod ............................................................................................................................. 15

4 Fabrication of Prototype ........................................................................................................... 16

4.1 Frame..................................................................................................................................................... 16

4.2 Suspensions ......................................................................................................................................... 17

4.3 Wheel Assemblies ............................................................................................................................. 18

4.4 Steering ................................................................................................................................................. 18

4.5 Minor Components ........................................................................................................................... 20

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4.5.1 Roll Cage ....................................................................................................................................................... 20

4.5.2 Brakes ............................................................................................................................................................ 21

4.5.3 Seat ................................................................................................................................................................. 22

5 Simulation ...................................................................................................................................... 23

6 Testing, and Debugging ............................................................................................................... 25

6.1 Planned Testing ................................................................................................................................. 25

6.2 Completed Testing ............................................................................................................................ 25

6.3 Debugging ............................................................................................................................................ 27

7 Business Plan .................................................................................................................................. 28

7.1 Intellectual Property ....................................................................................................................... 28

7.2 Marketing Study .................................................................................................................................. 28

7.3 Prototype Spending ............................................................................................................................ 28

8 Conclusion ..................................................................................................................................... 29

9 Acknowledgments ....................................................................................................................... 31

10 References ................................................................................................................................... 32

v

Table of Figures

Figure 1. Team Members .............................................................................................................................. 1

Figure 2. Complicated Frame Design ........................................................................................................... 2

Figure 3. Simple Frame Design .................................................................................................................... 2

Figure 4. Slider Mechanism Adjustability .................................................................................................... 3

Figure 5. Wire frame ..................................................................................................................................... 4

Figure 6. Solid frame .................................................................................................................................... 4

Figure 7. Primary Suspension of EP179808 ................................................................................................. 5

Figure 8. Primary Suspension Tie-Rod ......................................................................................................... 5

Figure 9. Suspension Linkage Variation ....................................................................................................... 6

Figure 10. Primary Suspension Final Design ................................................................................................ 7

Figure 11. Center of Gravity Sensitivity Study ............................................................................................. 8

Figure 12. Location of Center of Gravity ..................................................................................................... 8

Figure 13. Double Wishbone Suspension ..................................................................................................... 9

Figure 14. MacPherson suspension ............................................................................................................... 9

Figure 15. Swing-arm suspension ................................................................................................................. 9

Figure 16. Steering Sensitivity .................................................................................................................... 10

Figure 17. Rack-and-pinion ........................................................................................................................ 11

Figure 18. Steering Mechanism .................................................................................................................. 11

Figure 19. Drivetrain using splined shafts and U-joints ............................................................................. 12

Figure 20. Simple Moment Calculation ...................................................................................................... 13

Figure 21. Location of Lower Control Arm ................................................................................................ 13

Figure 22. FEA Simulation of Lower Control Arm .................................................................................... 14

Figure 23. Location of Connection Block ................................................................................................... 14

Figure 24. FEA Simulation of Connection Block ....................................................................................... 15

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Figure 25. Frame Fabrication ...................................................................................................................... 16

Figure 26. Suspension Fabrication .............................................................................................................. 17

Figure 27. Cam-lock Lathe Jig .................................................................................................................... 17

Figure 28. Front Hub ................................................................................................................................... 18

Figure 29. Rear Hub .................................................................................................................................... 18

Figure 30. Steering Tie-Rod Connection .................................................................................................... 19

Figure 31. Fabricated Rack and Pinion Steering ......................................................................................... 20

Figure 32. CAD Model with Roll Bar......................................................................................................... 21

Figure 33. Brake Mount .............................................................................................................................. 22

Figure 34. Brake Lines ................................................................................................................................ 22

Figure 35. Finished Prototype ..................................................................................................................... 22

Figure 36. Cornering at 0.4 g ...................................................................................................................... 23

Figure 37. Dynamic Simulation of Assembled Model ................................................................................ 23

Figure 38. Preliminary Testing ................................................................................................................... 26

1

1 Introduction

This document provides a summary of Team 15’s design report.

1.1 Team Members

Team 15 is comprised of four senior students at Calvin College. All plan to graduate in May 2013 with a

B.S.E., Mechanical Engineering concentration. The four team members shown in Figure 1 are (from left

to right): Meng Chen, Jacob VandeHaar. Nate Konyndyk, and Scott Kamp.

Figure 1. Team Members

1.2 Problem Statement

When a car corners, inertia pushes the car and its occupants opposite the direction of the turn. This can

create an uncomfortable feeling, depending on the nature of the turn, the speed, and the vehicle’s

dynamics. Our vehicle design is to combine aspects of various leaning vehicles in an innovative manner,

to create a passively leaning suspension. Our primary goal was to build and test our double suspension

design and prove that it works on a full scale vehicle.

Our prototype could serve as a platform for further development. Knowledge and data gained through this

research project can also form the foundation for later designs and improvements. If the prototype meets

performance specifications and is used as a platform for a production version, the vehicle will be aimed at

a very specific market segment: small performance car.

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2 Design

2.1 Design Norms

Cultural Appropriateness Swayspension is an innovative approach to solving issues associated

with driving. Our culture respects innovation and welcomes the

independence shown by differentiating our product.

Integrity As most race vehicles do, our project fully integrates form and function

into a performance-driven machine with aesthetics not burdened by but

rather defined by its purpose.

Caring We seek to provide a safe, reliable product which will improve user

comfort.

Transparency Our suspension will provide clear and predictable feedback for the

driver. It will be responsive, allowing the driver to feel the cornering

conditions of the vehicle and make appropriate adjustments as needed.

2.2 Design Challenges

2.2.1 Simplicity

The final design is much simpler than the original CAD model. An extreme example of this is the frame,

which was changed from having many members of round tubing (Figure 2) to only a few members of

square tubing at mostly right angles (Figure 3).

Figure 2. Complicated Frame Design

Figure 3. Simple Frame Design

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The secondary and primary suspension arms were also simplified in order to aid fabrication. Again, the

original design called for bent round tubing welded at complicated angles.

2.2.2 Manufacturing Capabilities

The resources available to us for fabrication of the prototype strongly influenced the design. For example,

had the resources been available to us, we might have designed the suspension arms to be laser-cut and

bent automatically. This would have avoided problems of heat warping from welding and saved much

time.

2.2.3 Adjustability

The prototype was designed with certain adjustable features to compensate for uncertainty in the design

and variations in testing conditions (e.g. operator weight). This was achieved through adjustable tie-rods

for the primary suspension spread, the slider mechanism preload tension (Figure 4), and the steering

linkage lengths. The adjustable steering linkages proved invaluable, as will be explained later. The slider

mechanism and secondary suspensions also allowed for a variable number of springs in parallel (again,

Figure 4). Finally, the secondary suspensions have multiple locations for the spring-holding pins to allow

preload adjustment.

Figure 4. Slider Mechanism Adjustability

2.3 Individual Component Design

2.3.1 Frame

The frame is the essential part of the design where safety is crucial. The frame needs to be strong enough

to support a person and withstand the forces applied on it due to use of the vehicle.

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Initially, the frame was drawn by plotting datum points in a CAD program. The points were connected to

form the wire frame shown in Figure 5.

Figure 5. Wire frame

This initial model enabled us to see where everything needed to be attached, and how the layout would

work. The frame could then been idealized for tubing size and shape using Finite Element Analysis

(FEA). From the FEA analysis and manufacturability considerations, the previous round tubing frame

design was switched to square tubing. This greatly simplified our manufacturing concerns as square

tubing is simpler to cut for welding and to attach tabs or bolts. The current design is shown in Figure 6.

Figure 6. Solid frame

Square tubing does have a minor disadvantage in its strength-to-weight ratio, but because overall weight

is not a concern, we determined square tubing was more than sufficient. The current design was greatly

simplified when we began physically building the frame but the overall geometry and locations of

connecting axes for the primary and secondary suspension systems remained the same. The frame design

also includes side rails to provide safety for the driver and to add support to the frame. FEA was

performed on the frame to ensure the design would meet all the strength requirements.

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2.3.2 Primary Suspension

The primary suspension is the main component that distinguishes our vehicle from all other designs. It is

what allows and simultaneously causes the vehicle to sway while cornering. It will give our vehicle a high

roll center, to allow the swaying motion to occur passively. It is also the component with the two most

critical connections—one to the frame and the other to the secondary suspensions.

We are using a simple linkage design that we found in several other places, but modifying it to make the

leaning motion occur passively, or as a result of the inertial sway of the body. An example from our

research is shown in Figure 7.

Figure 7. Primary Suspension of EP179808

An example of the linkage, with our adjustment and connections, is shown below in Figure 8.

Figure 8. Primary Suspension Tie-Rod

In order to lean while cornering, the center of gravity of the vehicle must be low enough relative to the

pivot point of the vehicle. The primary suspension linkages are designed to be substantially higher than

the wheels so that the vehicle’s center of gravity hangs below them. When the vehicle corners, the frame

shifts away from the apex, thereby forcing the suspension to tilt towards the apex.

The first problem that we needed to resolve was that the wheels would widen naturally, and the vehicle

would squat. We could see that there needed to be a support connecting both sides, to hold the vehicle up

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and the wheels in. We determined that a rod would suffice, since a spring would not be safe, and the

secondary suspension would compensate for the rough ride.

The geometry of the primary suspension controls the relative angle between the body of the vehicle and

the wheels. The relative angle can be adjusted by changing the length of the vertical linkages. We

determined that we want the vehicle to sway more than the wheels, to reduce the acceleration felt by the

driver and to maintain contact between the wheels and pavement. An exaggerated diagram of this is

shown below in Figure 9.

Figure 9. Suspension Linkage Variation

In Understanding Parameters Influencing Tire Modelingi, Nicholas Smith explores the relationship

between wheel camber and traction. The paper states “for wide street radial tires, camber force tends to

fall off at camber angles above 5°”. Therefore, 5° maximum camber change became a critical design

parameter for our vehicle. 11° maximum tilting for the frame was chosen by taking in to consideration

ground clearance. When the frame tilts toward either direction, the ground clearance decreases, limiting

how much frame tilting can be achieved given a certain wheel diameter. 11° provides significant

reduction to lateral acceleration (up to 20%) while keeping enough ground clearance.

Based the maximum camber change and maximum tilting angle, the linkage ratio for the primary

suspension has been set to be 1:1.85.

The variation of system center of gravity can be quickly estimated using the function

where D is the distance between the approximated roll center and the system center of gravity. We found

that the center of gravity will vary by only 2% of the vertical height distance between system center of

gravity and proximity roll center. This is about 0.5 inches in the worst case.

Theoretically, the frame is at a stable equilibrium when centered. But when taking into account internal

friction and resistance, the system could be considered to be in indifferent equilibrium. As such, the tilting

response curve will solely depended on the spring response because the center of gravity position change

can be neglected.

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Figure 10 below shows our final design of the primary suspension. We introduced a few simplifications

for manufacturability and ease of welding without compromising its integrity.

Figure 10. Primary Suspension Final Design

Having most of the primary and secondary suspension geometry defined, sensitivity analysis was

conducted to determine the ideal center of gravity position for the whole vehicle. Using the Mechanism

program in Creo Elements/Pro, force acting on a single point defined on the suspension is used to

represent centrifugal force concentrated on the center of gravity. Both the force parameter and center of

gravity parameter could be changed independently. The simulation showed the theoretical maximum

tilting that could be achieved. The goal was to keep the theoretical maximum tilting large and use the

primary suspension spring mechanism to fine tune the exact response curve.

Eight different center of gravity positions (measured downwards from an arbitrary reference height) and 4

different lateral acceleration conditions were simulated. The results are shown in Figure 11.

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Figure 11. Center of Gravity Sensitivity Study

As the center of gravity passes below a certain height threshold, the change in theoretical maximum

tilting diminishes. Therefore we choose a center of gravity height near the threshold to simplify the rest of

the design. The required center of gravity location is shown in

Figure 12.

Figure 12. Location of Center of Gravity

0

2

4

6

8

10

12

0 0.2 0.4 0.6 0.8

Sust

ain

ed

tilt

ing

(de

g)

Lateral acceleration (g)

CG vs. Tilting sensitivity Study

-75mm CG

-100mm CG

-125mm CG

-150mm CG

-175mm CG

-200mm CG

-225mm CG

-250mm CG

Actual center of gravity of

the vehicle

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2.3.3 Secondary Suspension

The Secondary Suspension is required in order to absorb road bumps as the Primary Suspension is unable

to do so. The double wishbone design is shown in Figure 13.

Figure 13. Double Wishbone Suspension

2.3.3.1 Design Decisions

Originally, the Secondary Suspension was designed as a MacPherson-type (Figure 14). This design was

rejected due to large camber change under load. A swing-arm-type suspension was also considered

(Figure 15).

Figure 14. MacPherson suspension

Figure 15. Swing-arm suspension

However, after switching to car wheels from bicycle wheels, the swing-arm design was rejected due to

durability and manufacturability concerns.

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2.3.4 Steering

Our steering mechanism must be reliable, responsive and user-friendly. Reliable steering control is an

important safety aspect for a vehicle. Vehicles must be controllable at all times; therefore, the steering

system needs to be designed with careful consideration to ensure the integrity of the linkages and joints

during the operation.

The responsiveness aspect of the steering relates to the steering angle sensitivity curve, the rate of wheel

angle changes to the rate of steering wheel angle changes. Ideally, the steering is less sensitive during the

first half rotation of the steering wheel and becomes increasingly sensitive as the rotation of the steering

wheel increases like illustrated in Figure 16.

Figure 16. Steering Sensitivity

Also, the steering control must be user friendly. The steering wheel response from the vehicle tilting must

be minimized, preferably eliminated completely. So, the wheel steering angle does not change with the

frame tilting.

Challenges for the steering mechanism design are mostly brought by the vehicle tilting motion. The

steering of the vehicle must be controlled while tilting. In order to accomplish this task, a standard rack

and pinion design will be able to perform sufficiently. In the rack and pinion design, the steering wheel is

directly connected to a rack and pinion gear which moves the push/pull rods which turn the wheels. The

rack and pinion design is shown in Figure 17.

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Figure 17. Rack-and-pinion

The face width of the pinion gear in the current design is significantly larger than the original design. The

width was increased from 0.5” to 1.25” in order to provide a stronger design. The pitch diameter of the

pinion was also increased from 1” to 1.75”. This shortens the maximum distance the rack must travel

when the steering wheel turns to only 4” in either direction. Due to the increase in diameter, the steering

wheel only needs to complete one 360-degree cycle to achieve the maximum turning. This results in

higher turning sensitivity as less of the steering wheel needs to be rotated in order to turn the vehicle.

The push-rod design is shown in Figure 18. The push/pull rods change depending on the direction the car

is turning. If the vehicle is turning left, the left rod becomes the pull rod and the right rod becomes the

push rod. This is switched when the vehicle turns right.

Figure 18. Steering Mechanism

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2.3.5 Powertrain

Our prototype will not include a powertrain. At our industrial consultant’s suggestion, we deemed the

powertrain to be outside the strict goals of the project. However, we are including the powertrain in the

design to maintain the integrity of the vehicle. Our prototype includes enough space so that a powertrain

could potentially be added if the project is continued. A CAD model of the powertrain is shown in Figure

19.

Figure 19. Drivetrain using splined shafts and U-joints

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3 Force Analysis

The model was simulated using FEA in Creo Elements/Pro. Analyses were conducted primarily on the

primary suspension component. The primary suspension lower control arm and the tie rod region are

susceptible to very high stresses compared to other vehicle components.

3.1 Primary Lower Control Arm

First, simple moment balancing calculations were used to estimate appropriate load in FEA simulation.

This is shown in Figure 20.

Figure 20. Simple Moment Calculation

The location of the lower control arm on the CAD model is shown in Figure 21 and the FEA-simulated

part is shown in Figure 22.

Figure 21. Location of Lower Control Arm

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Figure 22. FEA Simulation of Lower Control Arm

The FEA simulation shows the component can take 4.2 times the static load before it deforms

permanently.

3.2 Connection Block

Another important component in the design is the connection block. A connection block is located on

each of the lower control arms and supports these arms through a tie-rod. This in turn keeps the vehicle

supported off the ground. The location of this connection block is shown in Figure 23 and the FEA

simulated part is shown in Figure 24.

Figure 23. Location of Connection Block

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Figure 24. FEA Simulation of Connection Block

This component yields a safety factor of 17.

3.3 Threaded Tie-Rod

A simple equation is used to estimate the allowable load for the tie-rod. This equation is shown below.

For ½-20 rod, the maximum allowable load is calculated to be 14,541 lbs while the actual static load is

423 lbs. This means the threaded tie rod will have a safety factor of 7.7.

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4 Fabrication of Prototype

During the fabrication of the prototype, we needed or were forced to make adjustments, both to keep our

project within the scope of the class, and also to make it successful. In many cases, our capabilities and

time constrained our work. While fabricating a project on such a large time scale as ours, we needed to

keep aware of which parts are critical, and which are not. Some parts of the project, such as the floor, the

seat, and the locations of the steering wheel and braking system do not need to be precise. In these

instances, the fabricator needs to work very quickly, lest he or she spends lots of time doing non value-

added activities.

During the initial assembly stage, after the construction of the frame and suspensions, we encountered

many manufacturing defects. The result of welding pieces produced large variations in similar parts, such

that assembly became impossible. As our consultant warned us, our variation analysis proved invaluable.

We are forced to create flexibility in the system, while maintaining tight tolerances where necessary.

4.1 Frame

The frame was fabricated first so that other components could be attached as they were completed. The

lowest level of the chassis was welded first, and then the vertical members were welded on by sighting

along the chassis. A picture of the preliminary frame fabrication is shown in Figure 25.

Figure 25. Frame Fabrication

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After this the other members (roll-bar, uprights, and attachments for the floor, seat, and steering wheel)

could be welded on more rapidly.

4.2 Suspensions

Suspension fabrication began with welding sleeves (round tubing) to the arms (square tubing). Because

warping quickly proved to be a major issue, we built a custom jig to hold the sleeves perpendicular to the

arms and at the correct position. Warping was still present but was deemed acceptable. In some cases, the

arms had to be heated and bent to correct for warping (visible discoloration can be seen in Figure 26)

Figure 26. Suspension Fabrication

The other major issue in fabricating the suspension was with the bushings. We were unable to source

bushings to fit our sleeves, so we had to machine the outer diameter of each bushing lower. This process

was greatly aided by a cam-lock lathe jig (Figure 27).

Figure 27. Cam-lock Lathe Jig

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4.3 Wheel Assemblies

The fabrication of the wheels and hubs presented us with the learning experience of constrained design

and fabrication cycles. The front hubs/knuckles were collected at the beginning of the year from a

previous project (see Figure 28).

Because we had designed around the round knuckles, we needed to match their bolt pattern (4x100). This

proved more difficult than we had thought. Our wheels needed to be at least 24 inches in diameter, yet

have a relatively small bolt pattern. After finding our four similar wheels, we needed rear hubs with the

same bolt pattern. An online toolii was used to find cars with the matching the bolt pattern, from which

hubs were found at AutoZone. We selected the front wheel bearing and hub assemblies from a 2005

Saturn Ion because they had splined centers and could be bolted on by their flanges rather than press fit

(see Figure 29)..

Figure 28. Front Hub

Figure 29. Rear Hub

4.4 Steering

The steering mechanism was designed to be as responsive as possible in order to ensure the safety of the

driver and provide the most control. In order to achieve a fabricated version of the designed system,

tolerances and adjustability were required. We used a double tie-rod design because of our

unconventional suspension system. Because the frame sways when turning, we could not use a straight

tie-rod to connect the rack and pinion and wheel hubs. This created a challenge in order to still be able to

successfully turn the vehicle while the chassis sways. In order to accommodate this swaying motion, we

designed the system to use a double tie-rod using an intermediate connection between the rack and pinion

and front wheel hub. A picture of this is shown in Figure 30. Comparatively, a CAD model of the steering

connection is shown in Figure 18 above.

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Figure 30. Steering Tie-Rod Connection

Initially, the members of the steering system had too much slop and had to be corrected. The cause of the

slop came from loose tolerances on connector pins. These were fixed by creating an extra connecting

piece between the first and second tie-rods. This piece maintains the desired geometries between the two

tie-rods. These connecting pieces are also shown in Figure 30.

Another essential component in the steering system is the pivoting block that connects the two tie-rods.

This component was necessary to be able to accommodate the natural swaying of the car while turning.

This piece is also shown in Figure 30 above. These pieces were angled towards the outside in order to

provide Ackerman steering where the inside wheel turns sharper than the outside tire when turning. This

is necessary because the outside wheel travels along a larger radius than the inside wheel to prevent

slipping of one of the tires.

Another area where the system had slop came from the rack and pinion. The distance between the teeth of

the rack and pinion needed to be tighter than our initial design. This was corrected by adding a support

beneath the rack to heighten the rack in order to shrink the unnecessary distance between the two

members. A picture of the fabricated rack and pinion is shown in Figure 31.

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Figure 31. Fabricated Rack and Pinion Steering

Due to the importance and difficulty in achieving the correct geometries in the actual fabricated steering

system, several adjustments were made after initial testing before the desired geometries were finally

established. We purposely designed the system to be adjustable through the two tie-rod lengths between

the rack and pinion and the front wheel hubs. These tie-rods could be adjustable by changing the amount

the rods were threaded into the eye joints. By threading the rod further into the joints, the length of the tie-

rod shortened and by unthreading the rod from the joints lengthened the tie-rods which increased the

distance between the connector piece and the wheel hub. This was a quick and easy way to make the

steering linkages adjustable.

4.5 Minor Components

This section outlines the fabrication of the remainder of the parts of our prototype. These include the roll

cage, brakes, and seat.

4.5.1 Roll Cage

As one of the primary design goals is safety, a roll bar was obviously necessary to better protect the driver

in the event the vehicle flips while turning. The roll bar was designed to be tall enough so that it stands

above the head of the driver while giving some clearance. The frame must be rigid enough to withstand

the force of a rollover accident. In order to ensure the rigidity of the roll bar, the frame and two supports

were welded onto the existing frame. The roll cage of our vehicle was designed with the same strength

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material as the rest of the frame. It was located in the approximate mean position of a driver’s head, and

about two inches above that of a very tall driver.

The roll bar itself was fabricated by bending one inch square tubing to the desired angles using a tube

bending apparatus. The roll bar spans the distance of the width of the frame with enough shoulder and

head clearance. A picture showing the CAD model of the frame including the roll bar is shown in Figure

32.

Figure 32. CAD Model with Roll Bar

4.5.2 Brakes

Brake calipers and rotors were collected from the same project as the knuckles. The master cylinder was

found in the engineering storage from a previous project. A matching pedal with a modular mount was

fabricated (see Figure 33). Because we could not find long rubber lines either premade or custom, steel

lines had to be bent to allow for motion of the suspensions. This was achieved by curling extra line by the

pivot points of the components (see Figure 34).

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Figure 33. Brake Mount

Figure 34. Brake Lines

4.5.3 Seat

The seat of our vehicle was chosen because of its low profile and ease of mounting. It needs to keep the

driver as low to the ground as possible to keep the overall center of gravity low. A picture of the roll cage

and seat on our actual prototype are shown below in Figure 35.

Figure 35. Finished Prototype

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5 Simulation

Mechanism simulation was also conducted in Creo to determine the system response to various driving

patterns. Gravity conditions in CAD programs are easily manipulated to simulate the vehicle driving

straight, accelerated and decelerated, and cornering at various speeds. For simplification and fluidity of

the process, initial simulation was only performed on a single suspension. The center of gravity of the

total assembly was estimated and represented by a force load pointing towards the direction of

gravitation. The CAD model showing cornering at 0.4g is shown in Figure 36.

Figure 36. Cornering at 0.4 g

Sensitivity analysis was performed to determine the optimal center of gravity position and the threshold

position to achieve tilting. After obtaining the desired center of gravity range for the top-level assembly,

connections between the frame and primary suspension could be determined in more detail.

Figure 37. Dynamic Simulation of Assembled Model

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The complete vehicle was dynamically simulated to verify the design as shown in Figure 37. Light-

weight, complex components such as the wheels and steering assemblies were excluded from this

simulation to improve simulation capability. Several major concerns emerged from the simulation results:

Vehicle demonstrates minimal tilting without adding driver weight to the simulation. This means

our vehicle response might be too reliant on driver weight, physique and some other factor which

we cannot control.

To solve the issue of tilting sensitivity to driver condition, we could shift the center of gravity of

the frame down relative to the suspension. However, this causes clearance issue to the ground and

bigger wheels will be needed to compensate the clearance loss. Engine or battery weight was not

considered in this simulation. If placed properly, it would shift the center of gravity down

significantly.

Current conditions suggest that there might be a lateral-acceleration tilting activation threshold.

At 0.4-g lateral acceleration without a driver, the tilting was small. However, at 0.7-g lateral

acceleration the system achieved significant tilting.

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6 Testing, and Debugging

6.1 Planned Testing

One of the main goals of the project is to reduce the lateral acceleration the driver experiences while the

vehicle is cornering. Modern accelerometers, especially when paired with the power of smartphones, are

very capable and adaptable tools. We have already found an app that records acceleration data in all three

dimensions. We originally planned to mount the smartphone to a fixed part within the frame as we are

testing it, in order to take data while the car is moving. Because of time constraints this approach was

replaced with physical observations while the vehicle was moving.

In order to simulate driving, and because a drivetrain is beyond the scope of our project, we have

determined an alternate method of testing, which was to pull the vehicle behind a car up to speed, to

release it, and then drive the vehicle on a prescribed course.

The dynamic response of the frame at rest will be relatively simple. We will place the vehicle on a level

surface, and with two people, manually tilting the frame. When the individuals holding the frame let go, it

should return very close to the upright position, and in a relatively short time.

The individual components and subsystems will be tested in their final positions, at the time of assembly

to ensure their functionality and durability.

6.2 Completed Testing

As the initial assembly stage proceeded, and the prototype started to take shape, we began testing the

completed sections. Figure 38 below shows testing of the suspensions and springs at the time that one

suspension was completed.

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Figure 38. Preliminary Testing

As more of the prototype was completed, the parts were tested in their final location until the entire

prototype was ready for the full speed test

To test the springs and overall quality of our secondary suspension, we performed a static test on a flat

surface. Our estimates of the damping coefficient on the rear suspensions are about 0.25 and on the front

about 0.4. A casual observer will notice that the back suspension is nearly perfect and that the front is

overdamped—too stiff. The extra stiffness of the front is attributable to the added steering system

components and ball-joints.

After some initial dynamic testing, we concluded the vehicle performs at the desired specifications that it

was designed for. One of these specifications was the amount of sway the vehicle provides around a

corner. The vehicle was designed to allow 11 degrees of tilt angle and the measured amount of tilt was 11

degrees. This was a very promising result in our preliminary testing. The tilt angle was measured by a

static push test where the vehicle was standing still and the frame was pushed to the maximum limit.

Before the vehicle can be deemed safe enough for the public, more testing is required to ensure its overall

safety. We are planning on conducting additional tests on the safety of the steering, brakes, and roll bar to

ensure the safety considerations. We are also planning on conducting tests to determine the reduction of

lateral acceleration the driver feels while turning. One of our goals is to reduce the lateral acceleration by

a minimum of 20%. Modern smartphones, and specifically the embedded accelerometer, can make this

testing quite easy.

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The high speed test showed us that our vehicle is very durable, and stable enough to be handled at speeds

of up to 25 miles per hour. At these speeds both of our suspensions performed as expected and were

sufficiently independent of each other. The testing we have done confirms that the vehicle performs as we

intended it to.

6.3 Debugging

During the testing our vehicle, we determined that the slider mechanism was stronger than we anticipated.

Having both the front and the rear slider mechanisms attached prevented our vehicle from swaying as

freely as we intended. Even after some adjustments, we determined that having only one slider attached,

and the other disconnected provided the desired driving and swaying experience.

The steering mechanism needed alignment once it was installed. It took many small rolling tests before

the front tires were sufficiently aligned for the high speed test. Fortunately we built adjustability into the

length and position of the tie-rods so adjustment only took a few minutes each time.

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7 Business Plan

7.1 Intellectual Property

At the recommendation of several of our advisors, we are in the process of filing a provisional patent

application. Once that has been accepted, we and our attorney will be seeking business partners to take

our project to the next level. If you are interested, please contact the Calvin College Engineering

Department and ask to be put in contact with Scott Kamp.

7.2 Marketing Study

If we were to form a business around our design, we would first acquire a patent for Swayspension in

order to protect our intellectual property. By doing so, we protect our design from competitors and can

remain competitive in the market.

Similar sport vehicles with tilting suspensions were researched (Table 11). However, none of the vehicles

found have passive leaning, a defining feature of Swayspension.

Table 1. Similar Vehicles

Make Model Wheel

Layout

Leaning

Method Status Price

Mercedes-Benz F300 Life Jet Tadpole Active Concept Only

Carver Europe Carver One Trike Active Bankrupt € 30,000

GM Lean Machine Trike Active Concept Only N/A

The primary target audience for our product is the 21 to 45 year-old age group. This particular group is

more likely to pursue a product such as Swayspension compared with the age group of 45 to 54, while

still having significant earning power. Our target market is likely to spend more income pursuing

excitement and new experience. This desire could be satisfied by our Swayspension. Market related to

sports car and track days is relative small and privileged. However, it is equally lucrative and rewarding if

a company becomes successful.

7.3 Prototype Spending

One of the design goals is to create a quality product that can be easily manufactured. The manufacturing

side of this design goal was severely constrained by tolerance issues. Due to the complexity and shear

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number of components which need to fall on each individual axis, tolerances proved vital. Each

individual component was constrained to fall within only a few thousandths of an inch in order to

successfully assemble when we began manufacturing our design. Due to our personal limitations in

manufacturing, we determined that money was the only way to get around the tolerance constraint. This

resulted in a compromise between quality and expenses.

The actual prototype spending is shown in Table 2.

Table 2. Prototype Spending

Date Parts Merchandise Shipping Total

19-Feb 2 bushings 2.26 4.80 7.06

27-Feb 90 bushings, 12 rod-ends, 6 ball joints 274.58 6.77 281.35

1-Mar 12ft 3/4 rod 44.50 0.00 44.50

28-Mar 1x3 bar 36.88 6.71 43.59

1-Apr Pinion 47.76 0.00 47.76

5-Apr Rack 42.07 6.15 48.22

10-Apr 100 retaining rings, 56 bushings 83.04 5.47 88.51

17-Apr 1x3 bar 21.39 5.85 27.24

17-Apr 8 linear bearing 159.92 22.81 182.73

18-Apr 4 wheels, seat, seat belt 73.00 0.00 73.00

20-Apr 2 rear hubs 190.00 0.00 190.00

25-Apr 5/8 rod 15.00 0.00 15.00

29-Apr Paint 25.00 0.00 25.00

Total 1073.96

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8 Conclusion

The goal of our project was to design and build a functioning double suspension system that sports cars

could use. As our first semester feasibility study indicated, this project was indeed feasible. As we were

warned by our advisors, the fabrication and assembly would take longer than expected. We did not

anticipate all of the iterations, of both design and assembly.

We successfully fabricated the entire vehicle during the second semester, and its performance met our

expectations. As our feasibility study anticipated and our testing proved, both of the suspensions work

independently. We designed and installed steering and braking system that did not interfere with the

motion of the vehicle. Our static and dynamic testing showed that the vehicle leans 11 degrees, exactly

matching the design.

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9 Acknowledgments

Team 15 greatly appreciates the aid and support shown to us by:

Ned Nielsen - Team Advisor

Ren Tubergen - Industrial Consultant

Phil Jasperse - Shop Manager

Harbor Steel - Donations

Senior Design Team 17

Several fellow students for occasional help along the way

Family and friends

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10 References

http://www.Alan927.com

http://www.jumpjet.info/Classic-Games/Windows/RCT/Facilities/Coasters/Suspended/Suspended.html

http://wendolonia.com/bm/hammock_car.jpg

http://thekneeslider.com/archives/2009/01/29/wesll-4-wheel-leaning-suspension-system/

http://motorcyclesspecification.blogspot.com/2012/04/2012-can-am-spyder-rt-s-review.html

http://www.cyclingnews.com/features/photos/sea-otter-2012-danny-hart-jared-graves-and-tara-llanes-race-

bikes/220104

http://www.engr.colostate.edu/pts/Job/Understanding%20Parameters%20Influencing%20Tire%20Modeling.pdf

i http://www.engr.colostate.edu/pts/Job/Understanding%20Parameters%20Influencing%20Tire%20Modeling.pdf

ii http://www.roadkillcustoms.com/hot-rods-rat-rods/Wheel-Bolt-Pattern-Cross-Reference-

Database.asp?LugCount=4&StudSpreadInch=&StudSpreadMM=100