Suspension is the term given to the system of shock absorbers and linkages that connects a

vehicle to its wheels. The job of a suspension system is to contribute to the car’s handling and

braking for a better safety driving, and to keep the driver as isolated possible from bumps,

vibrations, etc. It is important for the suspension to keep the wheel in contact with the road

surface as much as possible, since all the forces acting on the vehicle do so through the tires.

The suspension also has the important task to protect the vehicle itself and any cargo from

PROBLEM IDENTIFICATION

Analyzing the current suspension there are several points that could be improved in order to

damage.

optimize the functionality of the suspension.

Design of suspension system

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DESIGN TOOLS

such as the three dimensional solid modeling of each component. The use of solid modeling

techniques allows us the computerization of many difficult engineering calculations that are

carried out as a part of the design process. Simulation, planning, and verification of processes

such as machining and assembly of the components of the suspension are some of the tasks

analysis of the stresses acting on each component to reveal the state of stress and failure on

the device.

The use of NX6 is very important, but the use of other tools is also necessary. These will be the

knowledge acquired in engineering mechanisms and design from our current and prior classes

such as mechanical design, mechanics of material, dynamics, etc.

2. DESIGN CRITERIA

Weight and loads:

Various tools were used in the development of our design. The NX software is used for tasks

that will be performed in NX. Also this software will be used to perform an engineering

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Weight is one of the main constrain that engineers must consider in mechanical design of any

component. First of all, when you design the suspension components of a minibaja, all possible

load scenarios must be taken into acount. This is highly important since the sum of the forces of

each different scenario will be distributed not evenly. After that, depending in the geometry of

the components, one or several spots will experience a max stress. Loads can be presented

considering two types. One is the static load where the weight has that important roll, and the

second one is the dynamic load that will be the one exerted by several race circuit conditions.

The weight of the components will be added up to find the resultant static load, and the

calculations will be focus at the critical points in the material. We will start the calculations

with the static load followed by the dynamic load in order to find these critical spots.

Average weight:

components range Average

(actual)

calculated

Frame (50-80) 65 97

Driver (75-115) 95 100

Engine and

Transmition

(40-65) 52.5 75

Suspension and

Accessories

(40-65) 52.5 90

TOTAL 265kg 362kg

(Table 2-1)

Materials

Materials selection is another important point to cover. There is a huge range of different

properties that can be achieved with the use of engineering materials, from composites to

many different alloys. We focused in three major goals when we try to find the best material

that meet our needs, such goals are: the material deformation with several impacts, the cost of

the material, and manufacturability. In the second place but not less important, we consider

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the weight of components and the operating temperature since this project is design to operate

at a temperature of 23.9 degrees Celsius. The material which best match these requisites was

the alloy steel 4130 which is also known as chromoly. Steel 4130 properties are explained in

detail in the following paragraphs.

Properties

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Properties chart:

Materials

Modulus of

elasticity

(GPa)

Yield strength

(MPa)

Tensile

Strength

(MPa)

Percent

Elongation

Density

(g/cmE3)

Alloy ti-6AL-

4V

114 830 900 14 4.43

Tungsten

(commercial)

400 760 960 2 19.3

Steel alloy

A36

207 220-250 400-500 23 7.85

AISI 4130

CHROMOLY

210 360.6 560.6 28.2 8

Stainless alloy

304

193 205 515 40 8

(TABLE 2-2)

AISI 4130 chromoly has Average properties that match a wide range of operating

scenarios, unlike it fails in extreme loaded conditions, those extraordinary cases were

calculated assuming top speed impacts, neglecting any driver maneuvers and without

applying braking.

Since the elongation range is considerably wide, we have found out that chromoly can be

an excellent option. A big range in the plastic region will give us a warning when the

components must be replaced, and it will also help us to avoid a sudden fracture. Also, the

yield strength is high enough to withstand several scenarios with considerable load range

without being deformed.

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LOADS

Horizontal impact

with a magnitude

of 80325 N

Static load

Horizontal force

impact

Vertical load due to the weight of the

vehicle with a magnitude of 1252 N

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3. DESIGN INTRODUCTION

OVERLOOK

The suspension designed for the

control arms that are attached to the

upright and the hub that is mounted on

the spindle, as shown in Figure 3.1. The

frame of the existing cart will have to be

modified in order to hold the top arm,

the bottom arm, and the shock absorber.

The following paragraphs will go more

in detail in the description of each

individual part.

Figure 3.1: Front view of the complete assembled

suspension.

Load due to falling

Highest suspension load generated due to

a fall of .5 Meters which has a magnitude

of 11,014.4 N

cart consists of two single

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PARTS

The top arm will be connected by a ball joint to the upright, and will be pinned to the frame,

and was designed to have an adjustable length. The top arm will consist of one solid shaft

that will have a nut fixed in the center and it will be threaded on both sides. The solid shaft

will fit into the two shafts that will have a hole at the ends. Both shafts will have an inner

thread and the ends will be secured by two additional nuts, one on each side. The top arm

was designed adjustable in length to take advantage of the track and the environment in

which the cart will be placed. For example, if the track only requires the cart to take right

turns the length of the arm can be adjusted to change the angle of the tire which will

minimize over steer. The range of the length of the upper arm can be adjusted between the

lengths of 420 millimeters and 480 millimeters. The ball joint that will have to be placed at

one ends of the arm will have to be placed into the arm by force. The following image

shows the finished arm.

Figure 3.2

The bottom control arm is considered a reinforced single arm. The bottom arm, like

the top arm, will be pinned to the frame and will be attached to the upright with a ball joint.

The bottom arm will also hold the shock absorber in place at approximately two thirds of

the whole length away from the frame. The bottom arm will have two connections that

were designed so that the shock will not have touch the top face of the arm. The dimensions

of the shock that we used will be given further on. If a shock with different dimensions is

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used, then the extrusions should be modified accordingly. In order to reduce the weight of

the bottom arm, material will be removed between the connection at the pin and the shock

absorber connection. In order to reduce the stress concentration we added two solid shafts

that form an “X”. The lower arm also contains a reduction in cross-sectional area. This was

done so that the bottom arm does not limit the tire’s turning angle. The ball joint that will

connect the arm to the upright will be put in by force, and the appropriate dimensions for

the lower control arm will be given further on.

Figure 3.3

The upright will hold the upper control arm, the lower control arm, the spindle, the

tie rod and the brake caliper. The control arm connections will be aligned vertically with

the spindle. The hole in which both the upper arm ball joint and the bottom arm ball joint

was given a diameter of 11 millimeters which will give a clearance of 1 millimeter. The hole

in which the spindle will be placed will be approximately in the center of the spindle. The

hole will perforate the upright. The upright has a small extrude of a thickness of 5

millimeters. This will not allow the hub to come into contact with the upright and cause

friction. In order to avoid a direct impact to the tie rod, the upright was designed to hold

the tie rod between the control arms and at the position farthest away from the front of the

cart. Additional extrudes were placed on the upright toward the front of the cart in order to

mount the brake caliper.

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Figure 3.4

The spindle will be placed by force into the upright. The spindle has three different

diameters. The largest diameter will be inserted into the upright. Then the following

diameters hold the hub in place. There is a gradual decrease of diameter in the two smaller

diameters in order to avoid the concentration of stress in the shoulder. The spindle will

also have a thread at the smallest diameter with a length of approximately 25 millimeters.

This will allow the tire rim to also be placed here and reinforced with a nut.

Figure 3.4

The hub will be mounted on the spindle and will also hold the disk. The main shape

of the hub consists of a large “X” which will hold the tire rim in place. The hub also has an

area in which the disk will be mounted. The hub was also designed with holes which allow

the disk to be tightly secured. The inside of the hub will also include the gradual decrease of

diameter between the two smaller diameters in order to match the design of the spindle.

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Figure 3.5

The disk that will be used in this suspension will be mounted on the hub in order to

reduce the length of the spindle. The disk will be close to the upright so that the brake

caliper can be mounted on the upright and perform its action.

Figure 3.6

MATERIAL

The material in which the parts where analyzed was using AISI 4130. Its ultimate tensile

strength was 560.5 MPa and its yield strength is 360 MPa. After some research we came

across AISI 4330 which has the same yield strength as the material before. However it has a

higher ultimate strength than the one stated above. We suggest using AISI 4330 in the

bottom arm which will be subjected to a higher stress under normal conditions.

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PROS

In comparison with the original design this new design has many pros and cons. One of the

advantages that our new design has is that the whole design has calculations behind it.

Another advantage is that our design has an adjustable upper arm that will allow the driver

to take advantage of the track and the environment in which the cart will be placed. Also

our design has a completely different lower control arm. The lower control arm is a single

arm that has a larger cross-sectional area that will reduce the normal stress of the part.

Also when taking into account the spindle, we added a chamfer in order to reduce the

stress that a shoulder will cause between the hub and spindle. Another advantage to this

design is that we placed the tie rod in the back of the assembly. The reason for this is to

protect the tie rod from a frontal impact. However there are some details that will make

our design less ideal.

CONS

One of the disadvantages to our design is that the lower arm compared to the current

design will weight a significantly more. Also another disadvantage to this design is that if

the upper arm were to be modified to a smaller diameter, it may fail even in static load.

Also another disadvantage to our design is that all of the parts must be machined.

4. 3D MODEL DRAWING

The 3D modeling was created using the software NX6 which has been a very helpful and handy

tool in the design. Within the next pages we can appreciate a series of pictures where every

component of the suspension is described. Also there are a couple is images where every single

component has been assembled in order to appreciate the final look of this suspension

prototype.

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Frontal left side view

Down side view

15

Upside view

True shading

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6. DRAWBACKS (LIMITATIONS OF DESIGN)

Just like any other design, this prototype suspension has some drawbacks, in other words there

are some limitations in its design. The following points do explain and develop such limitations:

MANUFACTURABILITY/MACHINE

It is very important for engineers to design for manufacturability. In other words the

components, parts or the entire assembly being designed need to be relatively easy to

manufacture. If a component can be easily manufactured, it means the productions costs can

be taken to a minimum and production speed can be improved. For this project it was taken

into consideration to design the components of the suspension to be ease to manufacture. In

other words most of the parts can be fabricated with basic tools.

The most challenging part to manufacture is the lower arm of the suspension. The frame of this

arm needs to be machined in order to obtain the best results. This lower arms was designed to

save weight, therefore mass was removed in designated points of the arm without scarifying

the integrity of the structure while some reinforcement were added where the mass was

removed. Such reinforcement is tubular in shape and need to be welded in place in an X shape

which adds some degree and difficulty to manufacture. The end link which attaches to the

upright is another point of the lower arm which is a little complex to fabricate. This is because it

is necessary to place a ball joint in this place which will hold the lower arm and upright

together. This ball joint base needs to be manufactured with very strict standards of

measurement in order to provide the best performance.

The upright is one of the most important parts of this system since it connects all parts of the

suspension together. Thus it was important for our team to come up with an efficient, strong,

light weight model. The model proposed is a very exceptional piece which its benefits are low

mass, light weight, improved use of space and durability. The drawbacks of this part are the

awkward shape of this part which increases the difficulty in manufacturability. The upright

needs to possess several connection links that need to be strong enough to hold the critical

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loads which the cart is going to be put into. Such links need to be welded in place, which means

change in geometry is going to be present leading to creating stress concentration factors.

Materials used as described before are going to be AISI 4340 and AISI 4130(most commonly

used as chromoly). Both steels are widely used in the industry which facilitated the ease of

access to them. Machinability of both alloys is considered to be done by conventional methods,

and best with the alloys in normalized and tempered conditions. Respecting to welding both

alloys is noted for their weld ability by all commercial methods. Materials are not really

considered as drawbacks.

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8. CONCLUSION

After an in depth analysis of each individual part of our suspension unit design we have come to

requirements. Some of the optimizations we have in mind include further analyzing the upper

control arm and possibly increasing its diameter; and also considering finding a more

appropriate ball joint for this part. In the optimization section of this report it was mentioned

that because of the increase in height of the bottom arm, we will need to find a more adequate

ball joint for this component that will adapt more to the modified dimensions and increase its

performance. After further review of our analysis we took notice that our spindle and upright

did not fail in any of the presented scenarios. This implies that the two parts that we designed

do not need additional modifications to improve their performance. Putting aside the analysis

of our design, we can say that each of our group members have become more familiar with the

useful tools that were applied during the design process. This includes the NX6 software,

knowledge acquired during lectures, as well as applying basic concepts of design. Furthermore

we had to use knowledge acquired from prior classes not just our current ones.

the conclusion that if we optimize our design it will be a good choice for this