In order to accomplish this task, different design aspects of a Mini BaJa@ vehicle were analyzed, and certain elements of the car were chosen for specific focus. There are many facets to an off-road vehicle, such as he chassis, suspension, steering, drive-train, and braking, all of which require thorough design concentration.
The points of the car that the University of Wisconsin Platteville decided to specifically focus on were the chassis, drive-train, and suspension.The most time and effort went into designing and implementing these components of the vehicle because it was felt that they most dramatically effect the off-road driving experience. During the entire design process, consumer interest through innovative, inexpensive, and effective methods was always the primary goal. 1 inch diameter tube with a thicker wall was used instead f 1. 5 inch diameter tube with a thinner wall for manipulability purposes. Although the thinner wall, 1.
5 inch diameter tube would be slightly lighter than the thicker wall, 1 inch diameter tube, it would have been more material and more difficult to weld.Safety Roll cage safety features were first implemented in Rules, which served as a baseline. The first primary safety standard focused on during design was maintaining a minimum of 6 inches vertical distance from the driver's head to the bottom of the RYO and a 3 inch clearance between the rest of the body and the vehicle roll cage. These dimensions created a roll cage envelope that was safe for the driver. After the roll cage FRAME DESIGN OBJECTIVE The objective of the chassis is to encapsulate all components of the car, including a driver, efficiently and safely.
Principal aspects of the chassis focused on during the design and implementation included driver safety, suspension and drive-train integration, structural envelope was created, the next aspect addressed during baseline design was roll cage structural integrity. Roll cage structural integrity guidelines can be found in the 2009 Baja SEA@ Competition Rules section 3, "Roll Cage, Systems, and Driver's Equipment. " All 2009 Baja SEA Competition Rules guidelines were implemented throughout the entire frame. Cross the front cross member at 135 degrees with respect to the top of the roll cage seemed to achieve the highest stress with the smallest load, and would be similar to a forward flip landing on the front of the roll cage. After some trial and error, a maximum distributed load of 80 lbs/in (1215.
20 lbs total) was determined to cause a stress of approximately 47,800 SSI in one of the 1020 steel members. This means that it would take approximately 121 5 lbs of load on the weakest member of the roll cage to cause a failure in the roll cage, as seen in Figure 8.Once the baseline requirements were met, other safety design points were implemented. The chassis was additionally designed to give the occupant extra space and protection with curved vertical supports and extra lateral bridge supports, which can be seen in Figure 1. These supports tie the right and left sides of the car together, increasing structural integrity and reducing the improve the roll cage safety and verify its structural integrity, finite element analysis was completed on the roll cage.
The results from these simulations are accurate for the type and amount of loading that was applied to the known material and geometry.However, these loading scenarios generally do not exactly represent an actual rollover crash. To accurately depict a rollover incident, dynamic loading would have to be used to simulate the types of impact loading that would occur during an actual rollover. It would be very difficult to accurately model this event without known data gathered from an actual rollover. This data could be gathered using strain gauges attached to the frame of the vehicle.
The results gathered from the FEE illustrate that the frame theoretically will not fail in a rollover until there is approximately 121 5 lbs of force on the weakest member f the roll cage.The FEE results show a design that meets the expectations set for this chassis. With the data collected from the FEE simulations, the roll cage was found to have a theoretical factor of safety of approximately 1. 87. Roll Cage FEE Safety Analysis Simulated loads within a computer program were placed on a wire frame model of the roll cage at critical points to simulate the amount of force that the vehicle would undergo from its own weight and a driver in the event of a rollover.To conduct a finite element analysis of the chassis, an existing chassis design was uploaded from the computer aerogram Silkworms@ to a finite element analysis program known as Algor@.
The loading performed by the Alger@ FEE software modeled an end over end rollover. Different loads at various angles were applied at points on the top of the roll cage to simulate that scenario, as seen in Figures 2 through 7. The weight of the vehicle itself was assumed to be 450 pounds. Then 200 more pounds were added to the vehicle weight to simulate the weight of a driver.
The combined values were used to model the loads exerted on the roll cage.The results show that with the total load of 650 pounds, distributed across the top of the roll cage, the frame will mound to be about one half the value of the roll cage's material yield strength. The maximum stresses and displacements are shown in Table 1. Safety Harness A five point racing harness attached to the most rigid members of the roll cage was utilized to ensure the maximum amount of driver safety restraint.
Attaching the seat belts to the most rigid and structural chassis components guarantees reliability of the seat belt under the extreme forces possible in a collision.Using a quarrelsome lever style seat belt clasp gives the driver the ability to get out of the vehicle in a safe amount of time in the event of an accident. SEA-8 requires that a driver be able to evacuate a Mini Baja car in less than five seconds. The safety restraints provided in the car will be sufficient for keeping a driver safe in the event of a collision, while still allowing the driver to escape in the required amount of time. Location of Load Relative to Roof of the Chassis 135 Deg 90 Deg 45 Deg 25580. 9 8644.
76 11923 Max Displacement (in) 0. 142465 Table 1: FEE safely results 0. 051976 0. 11683 Max Stress (SSI) Suspension and Drive-Train Integration Integrating the suspension and drive-train components off-road vehicle.
To complete the goal of integrating hose components efficiently and effectively, all the components were solid modeled in the computer aided modeling program SolidWorks@. After solid modeling was complete, all the components' restrictions and requirements were considered. A few key drive-train requirements to be included in the chassis design consisted of the distance the primary and secondary clutches needed to be apart and keeping the center of gravity of the vehicle as low as possible.A few important suspension requirements considered during In order to simulate a "worst case scenario", the yield stresses of the two different materials on the Mini Baja ar roll cage were found. Determining the yield strength of the roll cage is an important aspect, because once the materials begin to yield, the roll cage will lose much of its structural integrity.
The 1020 steel had a yield strength of 47,863 SSI, and the 4130 Chromo had a yield strength of 170,000 SSI.A loading configuration that would produce the highest stresses with the smallest load was then determined. Applying a distributed load 2 frame has a 555 Ft-lb/degree theoretical torsion's rigidity rating. It has been concluded that this meets expectation, and shows that the vehicle's frame is tractably suitable for the terrain it has to withstand.
The design of the chassis consisted of the angle at which the shocks needed to be mounted, the distance the Arms needed to be mounted apart, and the anti-dive angle in which the front and rear A-arms needed to be mounted.Once all requirements were compiled, the suspension and drive-train were integrated into the chassis design. Weight Keeping the frame as light as possible was a top priority. When power is limited, vehicle weight is a large factor in vehicle performance. The frame is one of the largest and heaviest components of the car, and which is why facial attention was placed on the vehicle's frame weight. The strategy utilized to minimize weight consisted of determining defined goals for the chassis accomplish those goals.
Once baseline safety design requirements were met, FEE aided the material decision making process. FEE specifically helped determine whether a member was under high or low stresses, in the scenarios discussed previously, making the chassis design process efficient and effective. Low stress chassis members were made out of 0. 049 inch wall thinness 4130 Chromo, and higher stress chassis members were made from 0. 065 inch wall thickness 130 Chromo. Chromo was chosen because of its weight reduction capability and beneficial material properties, as was stated previously.
Through accurately determining stresses on the chassis in different scenarios, weight reduction was able to be maximized through material selection and placement. The final weight of the chassis was measured to be 85 pounds. Another aspect of the chassis that was considered during the integration of the suspension was chassis deflection due to forces exerted through the suspension. To accurately minimize deflection in the chassis, FEE analysis was conducted and light weight Chromo uvular members were added where the deflection was greatest.The simulated loads conducted through FEE helped determine where and how additional members should be added to the chassis.
The method for simulating loads on the suspension points using FEE was similar to that of the rollover analysis, as previously described in the chassis safety section. Impact loading was simulated on the shock mounting points, at the angle in which the shocks were going to be mounted, until a member in the chassis reached its yield stress. Additional members were added to create the best combination of weight addition and structural rigidity.Each rear shock mount was able to withstand 800 lb of loading before yielding, as seen in Figures 9 and 10.
Each front shock mount was able to withstand 485 lb of loading before yielding, as seen in Figures 11 and 12. Based on the information presented above, the strength of these mounting points will be enough to withstand the forces exerted on them in extreme off-road conditions. Withstanding forces that simulate extreme conditions ensures rigidity and reliability in normal forbad conditions. Also, as a under normal loading, the fatigue limit of the material will not be exceeded.It is well known that 90% of all trial failures are due to fatigue, which is why it is so important that the stresses exerted on the chassis suspension mounts do not exceed their fatigue limit. Operator Ergonomics The ergonomics of a cockpit can noticeably affect the quality of an off-road vehicle driving experience.
This is why operator ergonomics was a factor that was considered in the design of the frame cockpit. The cockpit, consisting of the area in the roll cage where the driver sits to operate the vehicle, was designed for maximum comfort and ease of vehicle entrance and exit.The first aspect of the chassis that was designed around ergonomics was the firewall angle. The angle of the firewall, which inherently limits the amount an operator can lean back while driving, was set to 19 degrees, which is Just less than the maximum angle required by the 2009 Mini Baja SEA@ Competition Rules. Letting the driver lean further back gives a more relaxed position to drive the car. As the rollover FEE analysis shows, there were no detrimental effects to structural integrity found in leaning the firewall back for ergonomic purposes.
The next ergonomic improvement made to the chassis was side wall height.While still remaining thin the 2009 Mini Baja SEA-8 Competition Rules, the side wall height was set low enough to create easy entrance and exit, while still letting the driver remain safely encapsulated in the vehicle. The last specific ergonomic consideration made during chassis design was the decision to position the steering support in a way that makes it easy for people of all sizes to comfortably sit in the vehicle, while still being able to effectively support the steering column and house the Structural Rigidity Overall frame structural rigidity is important to enhance the capabilities of an off-road vehicle.To measure the verbal frame rigidity, torsion's rigidity analysis was conducted through FEE.
The objective of the torsion's rigidity analysis was to manipulate the chassis design within the FEE software to increase the amount of torque per degree of chassis deflection. By theoretically ability to be more transitionally rigid, making it able to withstand more intensive terrain without failure. To achieve this analysis, a simulated torque of 70 Ft-lb was placed on the back of the car, while the front of the car remained fixed, as seen in Figure 13.With the degree of rotation data collected from the FEE software, the torque as divided by the degree of rotation, creating a torsion's rigidity value for the frame.
The angle rotated under the 70 Ft-lb of torque was found to be 0. 126 degrees, as seen in Figure 14. The CHIP Mini Baja car 3 dashboard. The steering support remains out of the way of drivers' knees and additionally makes it easier to enter and exit the vehicle.
BODY AND COMPOSITES OBJECTIVES The purpose of the body is to prevent debris from entering the vehicle, with the intent of protecting the driver and the vehicle's components.The seat was designed to support the driver comfortably and safely while they are operating the vehicle. Manipulability All design work for the CHIP Mini BaJa@ frame was done using SolidWorks@. Using this program to produce a three dimensional model allowed easy revision of overbuild designs, and gave design team members a visual picture of what the frame would look like.
After the design of the frame was finalized, a list of required support members was created and exported to BendTech@, allowing easy bending and fitting of various tubular frame components.The CHIP Mini Baja car's body was kept very light through the use of HIDE plastic and fiberglass. Body Panels The body panels were made out of . 080 inch thick HIDE High-Density Polyethylene) plastic. HIDE plastic is a very light material that has desirable properties for a body panel.
HIDE Plastic has a tensile strength of 4,Pepsi, shear strength of 3,380 SSI, and it takes 4,570 SSI to cause a 10% deflection in the material. These properties also make the body panels more highly puncture resistant. The HIDE panels provide the components from rocks and other debris.When the panels were integrated into the car, the panels were recessed into the chassis to provide visibility to the chassis members, making the car aesthetically pleasing. Duds clips are utilized to affix the body panels to the icicle. Duds clips allow for the effortless removal of all body panels, providing access to all parts of the car.
Tube Bending To increase manipulability, many bends were used as opposed to miters. By implementing bends into the design of the frame, the number of cuts and welds were decreased.Decreasing the number of cuts and welds lowers the production cost and increases overall chassis strength. For example, by using more bends, a CNN tubing bender could be used during manufacturing, in place of hand welded miter Joints, reducing man-hours and production costs. All bends were designed to be add using a tube bender fitted with a 9-inch diameter die, which would eliminate costly tooling changes from the manufacturing process. Mounts All suspension mounts for the chassis were cut from 0.
1875 inch cold rolled plate steel, using a CNN laser cutter.The 0. 1875 inch cold rolled plate steel was chosen to give all mounts sufficient strength and durability while still allowing the chassis to remain light. Common materials throughout the manufacturing process eliminate costly and unique inventories, therefore lower the production cost. Hood and Dashboard The hood and dashboard of the car is made of E classmates and polyester resin.
E glass-mat is used because it is relatively inexpensive and provides the necessary properties to create an optimal hood and dashboard for the vehicle.E glass-mat has very good strength in all directions, compared too nun or bi directional fabric. E glass mat has short and very strong fibers. Using the equation in Figure 15, the hood and dashboard was calculated to have 66,000 SSI of tensile strength. This strength ensures the durability of the panels in all forbad conditions.
The hood and dashboard, like the body panels, are held on by Duds clips, which allow for easy access to all of the components in the front of the car.
