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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
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.
ii
Table of Contents
Team 15: Swayspension........................................................................................................................i
© 2013, Team 15 and Calvin College ............................................................................................................... i
Executive Summary ................................................................................................................................ ii
Table of Figures ...................................................................................................................................... v
1
2
Introduction .................................................................................................................................... 1
1.1
Team Members ....................................................................................................................................... 1
1.2
Problem Statement .............................................................................................................................. 1
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
3
4
Powertrain................................................................................................................................................... 12
Force Analysis............................................................................................................................... 13
3.1
Primary Lower Control Arm ......................................................................................................... 13
3.2
Connection Block............................................................................................................................... 14
3.3
Threaded Tie-Rod ............................................................................................................................. 15
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
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
Business Plan .................................................................................................................................. 28
7
7.1
Intellectual Property ....................................................................................................................... 28
7.2
Marketing Study.................................................................................................................................. 28
7.3
Prototype Spending ............................................................................................................................ 28
8
Conclusion ..................................................................................................................................... 29
9
Acknowledgments....................................................................................................................... 31
10
References ................................................................................................................................... 32
iv
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
v
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
vi
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.
1
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
2.2.1
Design Challenges
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
2
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
2.3.1
Individual Component Design
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.
3
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.
4
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
5
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.
6
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.
7
CG vs. Tilting sensitivity Study
12
Sustained tilting (deg)
10
-75mm CG
-100mm CG
8
-125mm CG
-150mm CG
6
-175mm CG
4
-200mm CG
-225mm CG
2
-250mm CG
0
0
0.2
0.4
0.6
0.8
Lateral acceleration (g)
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.
Actual center of gravity of
the vehicle
Figure 12. Location of Center of Gravity
8
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.
9
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.
10
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
11
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
12
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
13
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
14
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.
15
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 valueadded 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
16
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
17
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
4.4
Figure 29. Rear Hub
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.
18
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.
19
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 tierod 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
20
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).
21
Figure 33. Brake Mount
4.5.3
Figure 34. Brake Lines
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
22
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
23
The complete vehicle was dynamically simulated to verify the design as shown in Figure 37. Lightweight, 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.
24
6
6.1
Testing, and Debugging
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.
26
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
Wheel
Leaning
Layout
Method
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
Make
Model
Mercedes-Benz
Status
Price
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
28
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
19-Feb
2 bushings
27-Feb
90 bushings, 12 rod-ends, 6 ball joints
1-Mar
Shipping Total
2.26
4.80
7.06
274.58
6.77
281.35
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
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1073.96
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-racebikes/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
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