suny poly mechanical engineering technology capstone...
TRANSCRIPT
SUNY POLY
Mechanical Engineering Technology
Capstone Experience, MTC 420
Designing a BAJA Frame
Devinne Jalowiec and Curtis Jackson
7/14/2015
Dr. Tadros
Table of Contents:
Introduction ....................................................................................................3
Equipment ......................................................................................................3
Theory ............................................................................................................7
Procedure .......................................................................................................8
Analysis and Results ......................................................................................8
Discussion ......................................................................................................10
Teamwork ......................................................................................................10
Conclusion .....................................................................................................12
References ......................................................................................................12
Appendix A – Material Calculations .............................................................13
Appendix B – Frame Requirements ...............................................................19
Appendix C – Frame Design..........................................................................25
Appendix D – Rapid Prototyping ..................................................................28
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Introduction:
The intended goal is to design the frame for a Baja vehicle complying with standards put in place
by Baja Society of Automotive Engineering. The main points of the project will be design of the
frame, choice of material, a finite element analysis of the stresses present on the frame, and a
scaled 3D model.
The design of the frame must include proper clearances for driver fitment and appropriate
location for drivetrain. From the driver’s helmet to the frame of the baja vehicle there must be at
least six inches of clearance, and from the driver’s shoulders, torso, hips, thighs, knees, arms,
elbows, and hands they must have at least three inches of clearance. All while minimizing the
weight of the vehicle, but retaining maximum strength.
A comparison between standard 1020 DOM and 4130 chromoly with appropriate wall thickness
comparative to the specifications put into place by Baja will be completed to choose the most
appropriate material for usage.
The finite element analysis will be completed using symmetry since the vehicle will be
symmetric about the center plane. There will be four separate analyses based on a head-on
collision, rear-impact, side-impact, and a roll-over. The loads applied to the finite element
analysis will be derived from the average speed of the Baja vehicle just before the collision
occurs.
The model will be designed using weldments in Solidworks. In order to use weldments, the
sketch of the outline of the frame of the baja vehicle will first be created. Structural elements
will then be applied to the sketch. A scaled down model will be created using a rapid
prototyping machine.
Equipment:
For this project, we used Microsoft Excel. Microsoft can be reached twenty-four hours a day,
seven days a week at 1-877-696-7786.
Excel was very important in this project because it provided us with a way to organize all the
necessary data. Also, Excel is able to connect data in separate cells using equations.
The main page of Excel can be seen on the following page in Figure 2.1. From this page, one
can find the tools necessary to change the font, text size, font, color, and background color.
Excel is mainly used to create tables and graphs.
Once a template is created in Excel, it can be used for many different tasks. A template may be
difficult to create for some tasks, but once created the template can be used over and over again.
The benefits provided by Excel are almost endless, as one can organize any source of data using
multiple sheets, workbooks, or single one single sheet. Excel was used to material calculations,
Designing a Baja Frame
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a log for time spent working on the project, and a table to divide the necessary tasks into smaller
time periods.
Figure 2.1 – Excel main page
Also for this experiment, Solidworks was used for all the necessary modeling done to create the
frame of the baja vehicle. Solidworks can be reached at the following address:
Dassault Systèmes SolidWorks Corporation
175 Wyman Street
Waltham, MA 02451
They can also be reached by phone at 1-800-693-9000 in the United States and Canada.
Solidworks is also very important for this project because it allows us to accurately model the
frame of the baja vehicle.
The main screen of Solidworks can be seen on the following page in Figure 2.2. From the main
screen one is able to select a plane, create a new plane, or draw a 3D sketch. Once a plane is
selected the sketching tools become available. The sketching tools include: line, circle, spline,
rectangle, arc, ellipse, slot, polygon, and fillet/chamfer. Once the sketch is complete, one can
then extrude, revolve, or loft the sketch in order to create a 3D model.
For the project at hand, we used many different planes. To do so one needs to click on “Plane”
under “Reference Geometry” which is located under the “Features” tab. Planes other than the
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front, right, and top planes were needed because the frame of the baja vehicle needed to be
designed at many different angles.
Figure 2.2 Solidworks main screen
The main frame of the baja vehicle was first sketched using a total of 16 planes. Then
“Structural Elements” were used which can be found under the “Weldments” tab. The purpose
of using structural elements, is that it allows the user to add a profile to an entire sketch. For
example, the entire frame of the baja vehicle was sketch then the profile of a pipe was added to
see the correct joints and dimensions of the finished product. Structural elements are a quick
way to add much necessary detail to a model in a matter of seconds rather than minutes.
In order to create a scaled 3 dimensional model of the baja vehicle frame, a Dimension Elite
rapid prototyping machine produced by Stratasys was used. Stratasys can be reached through
their website at www.stratasys.com. An image of the rapid prototyping machine used can be
seen below in Figure 2.3 on the following page.
This machine made it possible to see how the finished product would turn out. With such a short
time frame it would have been impossible to design and construct the actual baja vehicle frame.
The Dimension Elite rapid prototyping machine not only made a scaled model possible, but it
also created the model in as little as thirteen hours and fifteen minutes.
Rapid prototyping is just a relative term. It means that using a rapid prototyping machine will
take less time to create the product at hand than conventional manufacturing methods. By no
means would thirteen hours to 3D print the baja vehicle frame be considered rapid; however,
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when compared to how long it would take us to produce it using conventional manufacturing
methods one can see how it would seem rapid by comparison.
Figure 2.3 – Dimension Elite rapid prototyping machine
An advantage to using this machine over a similar couterpart is that the dimension elite uses
soluble support technology. This soluble support is used to create a base for the model to begin
building off of when printed. Also, if the model being printed needs support material when
being constructed to withhold its integrity, these support materials will also be constructed of the
soluble support technology. Supports can then be dissolved using a water-based solution.
A specialty machine made by Phoenix Analysis & Design Technologies (PADT) was used to
remove all soluble support material present on the model and can be seen in Figure 2.4. PADT
can be reached at their headquarters at the following address:
7755 S. Research Dr.
Suite 110
Tempe, AZ 85284
They can also be reached by phone at 1-800-293-PADT. This device uses a proprietary fluid
which will dissolve the special support material but not the model material. The part is fully
submerged in to the heated fluid (up to 70º C) it then acts similar to an ultrasonic cleaner, and
gently pushes the fluid around the part.
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Figure 2.4 PADT machine used to remove soluble support material
Initally, we planned on completing a finite element analysis on the baja car as though it had
encountered a head on collision, rear impact, roll over and side impact using Autodesk
Simulation Mechanical 2013. Autodesk can be reached at the following address:
Autodesk, Inc.
111 McInnis Parkway
San Rafael, CA 94903
USA
Or by phone at 415-507-5000. Autodesk would be used to apply forces to our model and find
the stress present in the baja vehicle frame. However, when the frame was uploaded into
Solidworks as a 3D element the meshing of the model into separate elements took over twelve
hours and then crashed the computer. We attempted to import the frame as a solid model, a wire
frame, and then we attempted to re-draw the entire frame in Autodesk. This was again
unsuccessful when we ran the analysis on the model once forces were added. It was decided that
rather than waste useful time, we would calculate hand calculations for all of the impact
situations at hand.
Theory:
For the successful creation of a baja frame the frame must meet a very specific criteria of rules
set into place by SAE. In order to meet this the proper material must be selected according to the
strength of the steel. SAE uses 1018 DOM (drawn over mandrel) steel with an outer diameter of
one inch and a wall thickness of .120 inches as the minimum standard. Required will be the
comparison of the steels bending strength, and the cross comparison of the steels weight per foot
to find both the lightest, and strongest material to be used for a frames design.
All of the calculations done in this comparison can be found in Appendix A.
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Procedure:
1 – Complete material calculations so that the material of the frame is as strong as or stronger
than 1018 steel with an outer diameter of one inch and a wall thickness of 0.120 of an inch. For
a detailed material calculation see Appendix A.
2 – Design the frame of the baja vehicle being sure to abide by all frame requirements put in
place by baja SAE. For the specific requirements see Appendix B. A step-by-step process of the
frame design can be seen in Appendix C.
3 – Use the rapid prototyping machine in order to create a 3 dimensional scaled model of the baja
vehicle frame. See Appendix D for photos and a description of the process of 3D printing.
4 – Calculate the forces present on the baja vehicle frame in the event of:
- Head-on collision
- Rear-impact
- Side-impact
- Roll-over
These calculations can be seen in Appendix E.
5 – Complete hand calculations to determine the stress present on the baja vehicle frame in each
of these situations, and compare the stress to the maximum yield strength of the material.
Analysis and Results:
Initially, it was planned that after frame design we were going to complete a finite element
analysis for the baja vehicle frame simulating a head on collision, rear impact, side impact, and a
roll over. These simulations are very important when designing a baja frame for competition
because roll overs and other collisions are much more common than one would think. With the
results from these simulations the driver of the baja vehicle can rest assured that the frame will
protect him/her in the event of an accident. Autodesk Simulation Mechanical was going to be
used to complete the finite element analysis; however, we ran into multiple issues with the
completion of the analysis.
The analysis was unsuccessful. When the model was imported into the program from
Solidworks we generated a 3D mesh, and the mesh would not complete it simply repeated the
meshing process multiple times before simply erasing the entire model from the viewing screen.
The 3D mesh breaks the model up into individual elements and creates nodes where forces and
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boundary conditions may be placed. Therefore, the mesh is necessary in order to add any
boundary conditions or load.
Thinking the problem may have been caused by a problem in the frame design with Solidworks,
we went step-by-step through our entire design looking for sources of error. We made a few
minimal changes and attempted to mesh our model again using Autodesk Simulation
Mechanical. However, we again encountered the same error and decided to try another resource
to deal with the problem at hand.
We then attempted to use the simulation portion of Solidworks to complete a finite element
analysis. During a Solidworks class, one of our professors made it known that the simulating
technology of Solidworks is not accurate and is nowhere near up to par with that of other
programs. However, with the lack of success from Autodesk Simulation Mechanical we wanted
to try another program. We were able to add a load to the model and view the analysis of the
baja vehicle frame model with that load applied. The only downfall was that the load that we
had applied to the model would do nearly zero damage to the frame, and there was a great
amount of displacement present. Although, this analysis was again unsuccessful we were
pleased to see that we were able to complete a finite element analysis after the many hours spent
designing the frame. In Figure 5.1 below one can see the model in Solidworks after a nominal
load was applied.
Figure 5.1 Finite Element Analysis in Solidworks
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Discussion:
We intended on calculating the forces acting on the baja vehicle frame, as well as, completing
multiple finite element analyses of these forces. With this class only being eight weeks in the
summer, rather than a full sixteen week course during the spring or fall semester we knew that
we would be pressed for time. The design of the baja frame is what we both shared a genuine
interest in, and that is why we had chosen this project. In the end we see that we had bitten of
more than we could handle in such a short amount of time. Even with meeting two to three times
a week and working on our own during the week we were not able to complete everything we set
out to do. The design of the frame took much more time than anticipated with the strict
regulations put in place by baja SAE. It was important for us to design a frame that follows each
and every standard so we know in our future careers we will be able to design parts and
assemblies within the specifications put in place by not only the customer, but safety
requirements for the task at hand.
The biggest problem we encountered was attempting to transfer our model from Solidworks into
Autodesk Simulation Mechanical. Only one of us had taken a finite element analysis course, but
even with all notes and labs at our disposal we were not able to find an example that mirrored
what we were facing. It would have been more beneficial to have taken multiple finite element
analysis courses where more complex models where examined.
Teamwork:
Teamwork was very important for this project. The majority of the actual design of the baja
vehicle frame was done as a group so we would each have equal understanding of the process
and requirements put in place by baja SAE. Each member of the team worked approximately the
same amount of time on the project, as well as meeting between two to three times per week. At
these meetings, we discussed how the project was coming along, what needed to be next, and if
there were any problems that were encountered. The time spent on the designing the baja
vehicle frame by each person can be seen below in Table 7.1.
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Date Start Time
End Time
Time Elapsed Name Description
6/2/2015 16:45 17:30 0:45 Curtis Create project proposal
6/2/2015 16:45 17:30 0:45 Devinne Create project proposal
6/8/2015 16:45 18:45 2:00 Devinne Introduction and Material Calculations
6/8/2015 16:45 18:45 2:00 Curtis Introduction and Material Calculations
6/8/2015 20:00 21:00 1:00 Devinne Equipment and Frame design
6/8/2015 20:00 21:00 1:00 Curtis Equipment and Frame design
6/9/2015 16:30 18:00 1:30 Devinne Frame Design
6/9/2015 16:30 18:00 1:30 Curtis Frame Design
6/15/2015 16:45 18:00 1:15 Devinne Frame Design
6/15/2015 16:45 18:30 1:45 Curtis Frame Design
6/16/2015 15:30 18:30 3:00 Curtis Frame Design
6/16/2015 16:00 18:30 2:30 Devinne Equipment and Material Calculations
6/22/2015 20:00 22:45 2:45 Devinne Presentation for 6/22/2015
6/29/2015 16:20 18:30 2:10 Devinne Frame Design
6/29/2015 16:20 18:30 2:10 Curtis Frame Design
6/30/2015 16:20 18:30 2:10 Devinne Frame Design
6/30/2015 16:20 18:30 2:10 Curtis Frame Design
7/7/2015 18:00 20:00 2:00 Devinne Equiptment and Procedure
7/7/2015 20:45 21:30 0:45 Devinne Material Calculations, Outlining, and
References
7/8/2015 20:15 22:15 2:00 Devinne Edit Paper
7/8/2015 9:00 14:00 5:00 Curtis Paper and Presentation 7/14/15
7/9/2015 9:30 11:30 2:00 Curtis Paper and Presentation 7/14/15
7/11/2015 20:00 22:00 2:00 Devinne FEA
7/12/2015 16:15 19:30 3:15 Devinne FEA, hand calculations
7/12/2015 16:15 19:00 2:45 Curtis FEA
7/12/2015 20:30 21:30 1:00 Devinne FEA
7/13/2015 18:00 23:45 5:45 Devinne FEA, paper
7/13/2015 18:30 23:30 5:00 Curtis FEA, Paper, Presentation 7/14/15
7/14/2015 9:00 13:30 4:30 Curtis Presentation 7/14/15, Paper
7/14/2015 15:00 16:00 1:00 Curtis Presentation 7/14/15
7/14/2015 15:00 16:00 1:00 Devinne Presentation 7/14/15
Total Time 68Hrs
25 Min
Table 7.1 All hours spent on Capstone Experience by each team member
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Conclusion:
One of the goals for this project was to perform a finite element analysis; however, we were
unable to complete, due to reasons stated prior regarding the time span for this project, and our
miss calculation of how much time each segment would require. The design of the frame has
been a success we have been able to prove the worth of using 4130 steel over the current steel of
choice 1020 DOM. Through using the more capable material and a well thought through design
we have been able to design an overall much lighter frame then all previous years with a weight
savings of 18% from last year.
The greatest challenge for this project has been tackling the shortened time frame of eight weeks
compared to a standard of 16. If this project where to continue there will be time to go back and
look at the analysis again, and correct the issues between the modeled part and the appropriate
analysis program.
References:
Contact Us at SOLIDWORKS. (n.d.). Retrieved June 9, 2015, from
http://www.solidworks.com/sw/contact.htm
"Dimension Elite." About 3D Printer. N.p., n.d. Web. 07 July 2015.
<http://www.stratasys.com/~/link.aspx?_id=D66B9A2BC1CE4B2CA126E5FCDEA54D
BD&_z=z>.
"DOM Tubing (Drawn Over Mandrel)." DOM Tubing. N.p., n.d. Web. 07 July 2015.
<http://www.twmetals.com/1026-dom-tubing.html>.
"Locate Offices." <i>Autodesk</i>. N.p., n.d. Web. 13 July 2015.
<http://usa.autodesk.com/adsk/servlet/index?siteID=123112&id=304753>.
"SAE Collegiate Design Series." Rules & Documents. N.p., n.d. Web. 08 July 2015.
<http://students.sae.org/cds/bajasae/rules/>.
Sales and support. (n.d.). Retrieved June 9, 2015, from
http://www.microsoftstore.com/store/msusa/en_US/DisplayHelpContactUsPage/
"Seamless 4130 Alloy Steel Tubing." 4130 Tubing Supplier. N.p., n.d. Web. 07 July 2015.
<http://www.twmetals.com/4130-tubing.html>.
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Appendix A- Material Calculations:
Material calculations were need in order to choose the most appropriate material for the frame of
the baja vehicle. Baja SAE specifications state that the frame of the baja vehicle must be as
strong if not stronger than 1018 steel with an outer diameter of one inch and a wall thickness of
0.120 of an inch. The comparison consisted of two different materials 1020 DOM and 4130
Steel. For each of the materials, a material calculation was computed for the following sizes:
- Outer diameter of one inch and a wall thickness of 0.065 of an inch
- Outer diameter of one inch and a wall thickness of 0.120 of an inch
- Outer diameter of one and a quarter inches and a wall thickness of 0.065 of an inch
The material calculations of 1018 steel were computed to compare to the other material
situations, and can be seen below in Table 10.1.
Table 10.1 Material standard required by Baja SAE
It was important to remember when completing the material calculations to keep all units
consistent, in this circumstance it was decided to use metric units. The switch from inches to
millimeters is the only conversion factor needed, and it can be seen below.
1 inch = 25.4 millimeters
Sample calculations shown below are based off of the material standard required by Baja SAE.
The following equation was used to calculate the inner diameter of the pipe.
1018 Steel ( 1", 0.120 wall)
Outer Diameter= 25.4 mm
Wall Thickness= 3.048 mm
Inner Diameter= 19.304 mm
Modulus of Elasticity= 205,000 MPa
Yield Strength= 370 MPa
Distance to Extreme Fiber= 12.7 mm
Weight per foot = 1.13 lbs
Area Moment of Inertia = (π (Do4-Di
4))/64
13,615 mm4
Bending Strength= (Sy*I)/c
396,665 N-mm
Bending Stiffness= E*I
2,791,126 MPa-mm4
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Equation 1: 𝐼𝑛𝑛𝑒𝑟 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟 = 𝑂𝑢𝑡𝑒𝑟 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟 − (2 ∗ 𝑊𝑎𝑙𝑙 𝑇ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠)
𝐼𝑛𝑛𝑒𝑟 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟 = 25.4𝑚𝑚 − (2 ∗ 3.048𝑚𝑚)
𝐼𝑛𝑛𝑒𝑟 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟 = 19.304𝑚𝑚
Equation two below was used to calculate the area moment of inertia.
Equation 2: 𝐴𝑟𝑒𝑎 𝑀𝑜𝑚𝑒𝑛𝑡 𝑜𝑓 𝐼𝑛𝑒𝑟𝑡𝑖𝑎 = 𝜋(𝐷𝑜
4−𝐷𝑖4)
64
𝐴𝑟𝑒𝑎 𝑀𝑜𝑚𝑒𝑛𝑡 𝑜𝑓 𝐼𝑛𝑒𝑟𝑡𝑖𝑎 = 𝜋(25.4𝑚𝑚4−19.304𝑚𝑚4)
64
𝐴𝑟𝑒𝑎 𝑀𝑜𝑚𝑒𝑛𝑡 𝑜𝑓 𝐼𝑛𝑒𝑟𝑡𝑖𝑎 = 13,614 𝑚𝑚4
The following equations were used to calculate the bending strength of the material. The
variable “c” in Equation 4 below must first be calculated and its calculation can be seen below in
Equation 3.
Equation 3: 𝑐 = 𝑂𝑢𝑡𝑒𝑟 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟
2
𝑐 = 25.4𝑚𝑚
2
𝑐 = 12.7 𝑚𝑚
Equation 4: 𝐵𝑒𝑛𝑑𝑖𝑛𝑔 𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ = 𝑆𝑦∗𝐼
𝑐
𝐵𝑒𝑛𝑑𝑖𝑛𝑔 𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ = 370𝑀𝑃𝑎∗13,614𝑚𝑚4
12.7𝑚𝑚
𝐵𝑒𝑛𝑑𝑖𝑛𝑔 𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ = 396,665 𝑁 − 𝑚𝑚
Lastly, the bending stiffness of the materials can be calculated as shown below in Equation 5.
Equation 5: 𝐵𝑒𝑛𝑑𝑖𝑛𝑔 𝑆𝑡𝑖𝑓𝑓𝑛𝑒𝑠𝑠 = 𝐸 ∗ 𝐼
𝐵𝑒𝑛𝑑𝑖𝑛𝑔 𝑆𝑡𝑖𝑓𝑓𝑛𝑒𝑠𝑠 = 205𝐺𝑃𝑎 ∗ 13,614𝑚𝑚4
𝐵𝑒𝑛𝑑𝑖𝑛𝑔 𝑆𝑡𝑖𝑓𝑓𝑛𝑒𝑠𝑠 = 2,791,126 𝑀𝑃𝑎 − 𝑚𝑚4
The material calculations for 1020 DOM (drawn over mandrel) with an:
- Outer diameter of one inch and a wall thickness of 0.065 of an inch
- Outer diameter of one inch and a wall thickness of 0.120 of an inch
- Outer diameter of one and a quarter inches and a wall thickness of 0.065 of an inch
These material calculations can be seen in Tables 10.2, 10.3, and 10.4 respectively.
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1020 DOM ( 1", 0.065 wall)
Diameter= 25.4 mm
Wall Thickness= 1.651 mm
Inner Diameter= 22.098 mm
Modulus of Elasticity= 205,000 MPa
Yield Strength= 517 MPa
c= 12.7 Mm
Weight per foot = 0.65 Lbs
Area Moment of Inertia = (π (Do4-Di
4))/64
8,726 mm4
Bending Strength= (Sy*I)/c
355,241 N-mm
Bending Stiffness= E*I
1,788,919 MPa-mm4
Table 10.2 Material Calculations for 1020 DOM outer diameter of one inch and a wall
thickness of 0.065 of an inch
1020 DOM ( 1", 0.120 wall)
Diameter= 25.4 Mm
Wall Thickness= 3.048 Mm
Inner Diameter= 19.304 Mm
Modulus of Elasticity= 205,000 MPa
Yield Strength= 517 MPa
c= 12.7 Mm
Weight per foot = 1.13 Lbs
Area Moment of Inertia = (π (Do4-Di
4))/64
13,615 mm4
Bending Strength= (Sy*I)/c
554,258 N-mm
Bending Stiffness= E*I
2,791,126 MPa-mm4
Table 10.3 Material Calculations for 1020 DOM outer diameter of one inch and a wall
thickness of 0.120 of an inch
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Table 10.4 Material Calculations for 1020 DOM outer diameter of one and a quarter inches and a
wall thickness of 0.065 of an inch
The material calculations for 4130 steel with an:
- Outer diameter of one inch and a wall thickness of 0.065 of an inch
- Outer diameter of one inch and a wall thickness of 0.120 of an inch
- Outer diameter of one and a quarter inches and a wall thickness of 0.065 of an inch
These material calculations can be seen in Tables 10.5, 10.6, and 10.7 respectively.
1020 DOM ( 1.25", 0.065 wall)
Diameter= 31.75 Mm
Wall Thickness= 1.651 Mm
Inner Diameter= 28.448 Mm
Modulus of Elasticity= 205,000 MPa
Yield Strength= 517 MPa
c= 15.875 Mm
Weight per foot = 0.82 lbs
Area Moment of Inertia = (π (Do4-Di
4))/64
17,732 mm4
Bending Strength= (Sy*I)/c
577,490 N-mm
Bending Stiffness= E*I
3,635,145 MPa-mm4
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4130 Steel ( 1", 0.065 wall)
Diameter= 25.4 mm
Wall Thickness= 1.651 mm
Inner Diameter= 22.098 mm
Modulus of Elasticity= 205,000 MPa
Yield Strength= 600 MPa
c= 12.7 mm
Weight per foot = 0.65 lbs
Area Moment of Inertia = (π (Do4-Di
4))/64
8,726 mm4
Bending Strength= (Sy*I)/c
412,272 N-mm
Bending Stiffness= E*I
1,788,919 MPa-mm4
Table 10.5 Material Calculations for 4130 steel outer diameter of one inch and a wall
thickness of 0.065 of an inch
4130 Steel ( 1", 0.120 wall)
Diameter= 25.4 mm
Wall Thickness= 3.048 mm
Inner Diameter= 19.304 mm
Modulus of Elasticity= 205,000 MPa
Yield Strength= 600 MPa
c= 12.7 mm
Weight per foot = 1.12 lbs
Area Moment of Inertia = (π (Do4-Di
4))/64
13,615 mm4
Bending Strength= (Sy*I)/c
643,240 N-mm
Bending Stiffness= E*I
2,791,126 MPa-mm4
Table 10.6 Material Calculations for 4130 steel outer diameter of one inch and a wall
thickness of 0.120 of an inch
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4130 Steel ( 1.25", 0.065 wall)
Diameter= 31.75 mm
Wall Thickness= 1.651 mm
Inner Diameter= 28.448 mm
Modulus of Elasticity= 205,000 MPa
Yield Strength= 600 MPa
c= 15.875 mm
Weight per foot = 0.82 lbs
Area Moment of Inertia = (π (Do4-Di
4))/64
17,732 mm4
Bending Strength= (Sy*I)/c
670,201 N-mm
Bending Stiffness= E*I
3,635,145 MPa-mm4
Table 10.7 Material Calculations for 4130 steel outer diameter of one and a quarter
inches and a wall thickness of 0.065 of an inch
Based on the material calculations of 1018 steel, 1020 DOM, and 4130 Steel shown on
the previous pages, the material chosen for the construction of the frame of the baja
vehicle was 4130 steel with an outer diameter of one inch and a wall thickness of 0.065
of an inch. This decision is based almost entirely on the bending strength of the material
and the weight per foot of material.
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Appendix B – Frame Requirements:
Rules are given from SAE (found at http://students.sae.org/cds/bajasae/rules/ ) and are very
detailed and specific, in order to keep the competition both fair for all teams as well as safe for
the driver and others on the track, as accidents and roll overs do happen and these vehicles must
be capable of handling the abuse which they are dealt.
Lateral Space:
o A minimum spacing is required for the drivers fit in the roll cage
6 inches or 152mm from the drivers helmet
3 inches of 76mm for the drivers shoulders, torso, hips, thighs, knees,
arms, elbow, and hands.
These are for all competition drivers and must be measured when wearing
all of the approved equipment.
Roll cage Elements
o The roll cage is broken into Primary, and secondary members.
o Primary members include members are shown in Figure 11.1
Rear Roll Hoop (RRH)
Roll Hoop Overhead Members (RHO)
Front Bracing Members (FBM)
Lateral Cross Member (LC)
Front Lateral Cross Member (FLC)
Lower Frame Side Members (LFS)
o Secondary members include
Lateral Diagonal Bracing (LBD)
Side Impact Member (SIM)
Fore/Aft Bracing (FAB)
Under Seat Member (USM)
All Other Required Cross Members
Any tube that is used to mount the safety belts
o Secondary members must be steel and have a minimum wall thickness of .035in
or .89mm, and a minimum outside Diameter of 1.0in or 25.4mm.
o Roll cage members that are not straight must not be longer than 28in or 711mm
between supports. Small bend radii (<6in or 152mm) at a supported end of a
member are expected and are not considered to make a member not straight.
o The angle between two ends of a not-straight tube must not exceed 30º.
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Figure 11.1 Roll Cage Elements
Lateral Cross member
o Cannot be less than 8in or 203.5mm long
o Cannot have a bend; however it can be part of a larger bent tube between bends.
Rear Roll Hoop (RRH) Shown in Figure 11.2
o The RRH is a structural Panel behind the drivers back, and defines the back side
of the roll cage.
o The driver and seat must be entirely forward of this panel.
o The RRH may be inclined up to 20º from vertical.
o The minimum width of the RRH, measured at a point 27in or 686mm from the
seats bottom is 29in or 739mm.
o The vertical members of the RRH may be straight of bent and defined as
beginning and ending where they intersect the top and bottom horizontal planes.
o The vertical members must be continuous tubes
o The vertical members must be joined by LC members at the top and bottom.
o The LC members must be continuous tubes.
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Figure 11.2 Rear Roll Hoop (RRH)
Rear Roll Hoop Lateral Diagonal Bracing (LDB) Shown in Figure 11.3
o The RRH must be diagonally braced.
o Diagonal brace(s) must extend from one RRH vertical member to the other.
o The top and bottom intersections of the LDB members and the RRH vertical
members must be no more that 5in or 127mm form the RRH top and bottom
horizontal planes.
o The angle between the LDB members and the RRH vertical members must be
greater than or equal to 20º
Figure 11.3 Rear Roll Hop Lateral Diagonal Bracing (LDB)
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Roll hoop Overhead Members (RHO)
o The forward ends of the RHO members define points CR and CL (Figure 11.4)
o Points CR and CL must be 12in or 305mm forward of a point in the vehicles
elevation view, defined by the intersection of the RHO members and a vertical
line rising from the after end of the seat bottom.
o This point on the seat is defined by the seat bottom intersection with a 4in or
101mm radius circle which touches the seat bottom and the seat back.
o The top edge of the template is exactly horizontal with respect to gravity.
Lower Frame Side Members (LFS)
o The two lower frame side members define the lower right and left edges of the
roll cage.
o These members are joined to the bottom of the RRH and extend generally
forward, at least as far as a point forward of every driver’s heels when seated in a
driving position
o The forward ends of the LFS members are joined by an LC, the front lateral cross
(FLC)
o The intersection of the LFS members and the FLC defines the points AFR and
AFL
Figure 11.4 Lateral cross members
Side Impact Members (SIM)
o The two side impact members define a horizontal mid-plane within the roll cage.
o These members are joined to the RRH and extend generally forward, at least as
far as a point forward of every driver’s toes, when seated in a driving position
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o The forward ends of the SIM members are joined by an LC.
o The intersection of the SIM members and this LC defines the points SFR and SFL.
o The SIM members must be between 8in or 203mm and 14in or 356mm above the
inside seat bottom.
Under seat members (USM)
o The two LFS members must be joined by the Under Seat members.
o The USM must pass directly below the driver where the template in RC3
intersects the seat bottom.
o The USM must be positioned to prevent the driver passing throught the plane of
the LFS in the event of a seat failure.
Front Bracing Members (FBM)
o Front bracing members must join the Rho, the SIM and the LFS.
o The upper front bracing members (FBMUP) must join points C on the RHO to the
SIM at or behind points SF.
o The lower Front Bracing members (FBMLOW) must join points AF to points SF.
o The FBM must be continuous tubes.
o The angle between the FBMUP and the vertical must be less than or equal to 45
degrees.
o If a Front FAB is used there is no angle requirement between FBM and vertical.
Figure 11.5 Bracing
Fore/Aft Bracing (FAB)
o The RRH must be restrained from rotation and bending in the elevation plane by a
system of triangulated bracing.
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o Bracing must either
Rear bracing- directly restrain both points B from longitudinal in the event
of failure of the joints at points C.
Front bracing- restrain both points C from longitudinal and vertical
displacement, thus supporting points B through the RHO members.
o Members used in the FAB system must not exceed 40in or 1016mm in
unsupported length.
o Triangulation angles must be at least 20º
Front Bracing
o The Front systems of FAB must connect the FBMUP members to the SIM
members (on the same sides).
o The intersection with the FBM up members must be within 5in or 127mm
measured as a straight-line distance from centerline to centerline of points C.
o The intersection with the SIM members must be vertically supported by further
members connecting the SIM members to the LFS members.
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Appendix C – Frame Design:
The frame was designed as three segments utilizing the material which best fit each one.
Primary members can be seen below in Figure 12.1
o These members are all using 4130 steel with an outer diameter of 1inch and a wall
thickness of 0.065 of an inch.
Figure 12.1 Primary members of the baja vehicle frame
Secondary members
o These members are highlighted in green in Figure 12.2, and are all made using
4130 steel with an outer diameter of 1inch and a wall thickness of 0.065 of an
inch.
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Figure 12.2 Primary members in red and secondary members in green
Tertiary members
o These members are made using either 4130 with an outer diameter of 1 inch and a
wall thickness of 0.065 of an inch (highlighted Dark grey) or 4130 with an outer
diameter of 1 inch and a wall thickness of 0.035 of an inch (highlighted light
grey). Both can be seen below in Figure 12.3.
o The reason behind choosing two separate material sizes for these members are
due to what they are used for.
o The Dark grey members are there to support the drivetrain mounts, as well as the
driver in the event of a rear impact collision.
o The light grey members are simply added features to either add a minimal safety
aspect, or help to pass another set of ruling for safety.
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Figure 12.3 Finished Baja vehicle frame including primary, secondary, and tertiary members.
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Appendix D – Rapid Prototyping:
Rapid prototyping works by extruding a heated malleable plastic on to a tray and layering in a
support material to help achieve the desired part. The printer we used to prototype models of our
frame for us was a Dimension Elite. This printer utilized abs plastic as the model material, and a
special soluble support material to make cleaning the part a simple and easy process.
Figure 13.1 shows the inside of the printer used, you can see the extruder and heater element in
the upper right-hand corner and the printing base is the black tray on the bottom.
Figure 13.1 Inside of the Dimension Elite rapid prototyping machine
The printer lays down a couple of layers of just support material. This allows the part to snap off
the tray easily and a level printing surface of the part. The creation of the support material can
be seen in Figure 13.2.
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Figure 13.2 Creation of support material
As the rapid prototyping machine continues to print, the base tray lowers itself to allow the part
to gain height. In Figure 13.3, one can see how the base tray lowers by noting the difference in
dimension from the base tray to the extruder compared to Figure 13.2.
Figure 13.3 Base tray lowers as the material creating the part builds up in height
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The first completed part can be seen in Figure 13.4.
Figure 13.4 First completed 3D model of the baja vehicle frame
Upon close inspection some issues with the printed layers in the model appeared. This was due
to improper support of those segments. We decided to try another print with a different support
system in hopes to eliminate the bad layers. This method was indeed successful, however it did
use more support material then the previous attempt as can be seen in Figure 13.5.
Figure 13.5 Second completed 3D model of the baja vehicle frame
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In order to remove the support material a specialty machine made by PADT was used and can be
seen in Figure 13.6. This device uses a proprietary fluid which will dissolve the special support
material but not the model material. The part is fully submerged in to the heated fluid (up to 70º
C) it then acts similar to an ultrasonic cleaner, and gently pushes the fluid around the part.
Figure 13.6 PADT machine used to remove soluble support material
The model being placed in the bath of heated fluid and the model submerged in the heated fluid
are shown in Figures 13.7 and 13.8 respectively.
Figure 13.7 Model being placed in the bath of heated fluid
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Figure 13.8 Model submerged in the heated fluid to remove the soluble material
After the part has been submerged for an extended period of time, depending upon the amount of
support material, size of the part, and quantity in the wash, the soluble material is completely
dissolved and only the model remains. Both models with all soluble support material removed
can be seen in Figure 13.9.
Figure 13.9 Finished models of the baja vehicle frame with all support material removed