INTRODUCTION
7| Bl y communicates closely with suspension in the design of the rack to produce competitive turning radii and other steering and handling characteristics. Baja competition vehicles haven't changed much in the last five years, schools that perform well are highly tuned and perfect vehicle designs. Furthermore, the sudden introduction of the 4WD requirement put all the teams on equal footing - with no well-tuned previous vehicles it would be very difficult for us to compete with schools as historically successful as Saxon Racing for 2WD in the 2019 -2020 select. season.
All work in the 2019-2020 season is characterized by a connection with the installation of a four-wheel drive. Additionally, throughout the season I contributed to the design of the front suspension components, primarily creating a buildable upright suspension.
CHASSIS DESIGN
Design Constraints
- Structural Material Requirements
- Primary and Secondary Location
- Member Requirements
- Capability Restrictions
Roll cage members shall be made of steel tubing and may be straight or bent. Geometrical requirements on the frame are mainly related to the clearances between the driver and the envelope of the vehicle. These limitations often lead to the use of cuts on the frame to extend the envelope of the frame.
There are additional geometric requirements that specify dimensions that must be met regardless of the driver. The attachment of the rear FAB system must be within 51 mm (2 in) of point B, point S and point A on each side of the vehicle.
Design Goals
Weight Reduction
12 | Additional connection is considered part of the FAB system, and is subject to B.3.2.1 - Member requirements, but can be formed using multiple joined members, and this assembly, from end to end, can cause a bend of more than 30 degrees. The die is for an inside radius of 4½”, therefore the centerline radius of all tubes on the vehicle is set to 5” for Secondary (1” OD) and 5 ⅛” for Primary (1¼” OD) tube members. The process of bending with any of these methods is significantly less accurate and repeatable than a CNC tube bender.
Complicated nodes require grinding to fit properly, which adds time and reduces precision. Some of these members are not required structural members and do not have to meet external material requirements; use of primary material in these areas is unnecessary.
Ease of Manufacture
Additional Goals
Design Decisions
- Nose vs. Non Nose
- Curved FABlow
- Single Braced SIM
- FEA ANALYSIS
A decisive aspect of the design choice is whether front bracing elements will be used. Adding them connects the curve in FBMup to the point on the SIM. The 4WD system requires about 6" of additional length in the cockpit to make room for the front differential and front driveshaft. The geometry requirements precluded a noseless vehicle without front struts (Figure 6), so a nose-style design was chosen (Figure 7). .
With FABlow as a single curved piece, cutting and welding production time is reduced. The length of the SIM card path exceeds 33 inches and the bend is below 30°. The article requires only one additional support element in accordance with rule B.3.2.4. If the length of the SIM card path was less than 33 inches, the member would not need any additional struts.
The shape of the driver's cabin, especially the angle of the LFS, has been changed to accommodate this angle. With the chassis and input angle aligned, the driveshaft runs evenly down the side of the vehicle (Figure 13). The footwell compartment has been made wider and longer to house the front differential and axle shafts.
Load Analysis
Impulse Equation
I was responsible for the FEA analysis of critical components not only for the chassis but also for the front suspension links. It also requires a coefficient to account for the inertial mass of the vehicle to convert the dynamic problem into a static problem.
Parametric Plots
I determined the impact times by consulting video footage of Alfred's previous vehicles and corroborating with footage from other schools.
Chassis FEA
FABup Rollover
In the worst case, however, the peak stress experienced is smaller than the yield stress of the material. The reinforcement designs and shape of the SIM are highly variable; my team couldn't rely on historical data. A side impact refers to the impact between the side of the frame and the ground in a horizontal plane.
The wheel lock force exerted by the caliper on the rotor will be felt through the uprights, through the caliper bolts. Calculations carried out by the front suspension team identified the wheel lock force as 300lbf. The desired FOS for this component is 1.3 and the desired fatigue life for this scenario is to exceed 3,000 cycles. The lower A-arm is unspun; it will not experience forces of the magnitude experienced by the upper one. My team lubricated the tubes and the dies of the pneumatic bender to prevent them from kinking.
37 | P a g e The bar is vertical in the cockpit and then curves inwards and backwards as it travels to the top of the frame. At the top of the frame the element should bend so that it is perfectly horizontal and runs straight to the back of the frame (perpendicular to the front plane). I would accept the increased width at the top of the frame that this would cause.
The nodes of the frame are the points where three or more members meet at one point. The proximity of the fuel tank to the FABup (Figure 14) is a direct design flaw. FAB rear systems must create a structural triangle in side view on each side of the vehicle.
SIMmid Side Impact
Front Uprights
- Braking Scenario
- Vertical Drop
- Forward Impact
- Summary
Front upright beam loading is not cyclic, but conservative fatigue life estimates can be obtained from the S-N curves for this scenario. If the load in this area turns out to be too great, it can be reduced with a small design change. The maximum upright load was 15.5ksi in the upright position, corresponding to a safety factor of 2.52.
Our shock absorbers are mounted on the upper A-arm, which is attached to the post with a bolt. The front posts are complicated and expensive components that the team does not have a backup for. 27 | P a g e Using the conservative load model, the post has a factor of safety of 1.57 and converges on the solution.
In this crash scenario, the wheel will be pulled outward and the post will rotate until it is held by the bolts connected to the A-arms. If this area is deformed, it will be deformation that blunts the edge of the bolt hole and reduces the local stress. It is worth noting that under this load condition, calculations show that the bolt would fail well before the vertical.
The suspension team calculated that the maximum force the tie rod will exert on the upright is 500 lbf. The upright was analyzed under these conditions and the mesh was refined in the critical region shown. The high safety factor in this region led to a topological investigation on this part of the upright and material was ultimately removed.
A-Arm FEA
Vertical Impact
Forward Impact
Convergence is not as clear in this case, but the general trend is lower stress values as the mesh is refined.
MANUFACTURE
Equipment Selection
This choice meant that all the bending operations had to be done by myself and team captain, Austin Gibson. The manual pipe bender was selected for use in the bending operations, notching operations were performed with a manual pipe notcher and adjusted with angle grinders and dremel.
Issues and Resolutions
LESSONS LEARNED
Non-Planar Bends
The manufacture of the frame could have been made an easier and faster process with some changes at the design table. In terms of setup, it was very difficult and time-consuming to figure out how to orient the element in the pipe bender. Once the correct orientation was determined, it was still difficult to achieve this orientation within a tight tolerance.
Nodes
Tolerances
CONCLUSION
40 | P a g e m.) RRH Refers to the entire rear roll bar composed of two side pieces and . two side cross n.) LDB Lateral Diagonal Brace o.) LDB Cross Brace . p.) LC Lateral Crosses connect the left and right halves of the chassis. The RRH is a planar structure behind the driver's back and defines the boundary between the front half (front) and rear half (rear) of the roll cage. The vertical members of the RRH may be straight or curved and are defined as beginning and ending where they intersect the upper and lower horizontal planes (points AR and AL, and BR and BL in Figure B-8).
The vertical members must be connected at the bottom and top by ALC and BLC members. If a spigot is used to brace the RHO and RRH to achieve the lateral clearance in Rule B.3.3.1 - Side clearance, the added members must be a primary material (B.3.2.16 - Roll cage material); Gusset members connecting the SIM to RRH or FBM for the purposes of achieving the lateral clearance in Rule B.3.3.1 - Side space may be primary or secondary material (B.3.2.3 - Secondary members) and must be closed with Body become Panels.
Front bracing members must join the RHO, SIM and LFS at points C, D and F. The angle between the FBMUP and the vertical must be less than or equal to 45 degrees. Each triangle must be aft of RRH, include the RRH vertical side as an element, and have a vertex at point B and a vertex at either point S or point A.
The members that form this structural triangle must be continuous members; but bends of less than 30 degrees. The third (rear) vertex of each rear thrust triangle, Point R (Figure B-19), must additionally be structurally connected to whichever Point, S or A, is not part of the structural triangle. This additional connection is considered part of the FAB system, and is subject to B.3.2.1 - Member Requirements, but can be formed using multiple joined members, and this end-to-end assembly can be a bending of greater than 30 includes deg.
