Gives you guide to design and analyse the baja vehicle chassis for circular tube....
DESIGN and ANALYSIS of a Baja vehicle chassis Sunnel Daniel1, Saurabh Bhandare2, Kaushal Joshi3, Ajinkya Bhonge4 Ajay Kashikar5 1234
Final Year Students of ,Lokmanya Tilak College Of Engineering , Asst. Prof , Department of mechanical engineering, Mumbai University [email protected]
ABSTRACT :- This project aims at enriching student's knowledge on the basic systems and components of an all terrain vehicle. Their uses and importance is unique to the vehicle quite different from a normal automobile. It will also enrich student knowledge concerning various softwares like Pro-E, NX, Nastran, Ansys, etc that would help in better design and analysis of the all-terrain vehicle and thus improve the overall statistics of the vehicle making it better in terms of handling, durability, serviceability, accessibility and detecting and troubleshooting . Keywords-CAD of chassis,CAE of Chassis,Design of Baja Vehicle
1.0 Introduction The need for travelling in different types of terrain has laid the development of the all terrain vehicle which would help man travel in many different types of terrain where a normal passenger car would not be able to function at its optimum level. The different types of terrain would include sand, mud, rocks, jungle terrain, grass, concrete, etc. The vehicle would need an in-depth design and analysis of the chassis considering the adverse conditions which would affect the vehicle during its functioning.
2.0 Objective The objective is to achieve an optimized design after testing so that an entire vehicle can be designed for surviving the off-road challenges such as bumps, steep climbs, mud and dust terrain, sand dunes, etc. The chassis should be at an optimum while designing and fabricating an off-roader. There are different types of excitation frequencies that would be offered by the road and the chasis should be able to resist and absorb all the vibrations. This will help in better handling of the car, it will have improved stability, and will also protect the car from any damages during functioning. Various other specifications and hard points would have to be decided that would help in better functioning and surviving of the car. Various softwares like ANSYS, NX NASTRAN, Pro-E would be used for designing and testing the finalized designs of each assembly and components. Validation methods would be used to analyze, recheck the actual performance of each system In real life . The design of the chassis will be done on the basis of SAE BAJA norms, which will help us to go realistic way in the designing of terrain vehicle.
3.0 Material Selection
3.1 The requirement
Roll cage must be space frame of tubular steel as per the SAE BAJA norms. The material used for the Primary Roll Cage Members must be: A. Circular steel tubing with an outside diameter of 25 mm (1 in) and a wall thickness of 3 mm (0.120 in) and a carbon content of at least 0.18%. OR B. A
steel tube with bending stiffness and bending strength exceeding that of circular steel tubing with an outside diameter of 25 mm (1 in) and a wall thickness of 3 mm (0.120 in) and a carbon content of 0.18%. The wall thickness must be at least 1.57 mm (0.062 in), regardless of material or section size. Calculations must be presented at Technical Inspection which proves sufficient bending stiffness and bending strength. All calculations must be in SI units. Invoices or other evidence of the properties of the roll cage materials must be attached to the calculations. Calculations must be performed using three significant figures to the nominal tube sizes as specified by the invoice. The bending stiffness and bending strength must be calculated about a neutral axis that gives the minimum values. Bending stiffness is considered to be proportional to the product EI Where: E: Modulus of elasticity (205 GPa for all steels) I: Second moment of area for the structural cross section Bending strength is given by: SyI/C Where: Sy : Yield strength (365 MPa for AISI 4130 Steel*) C: Distance from neutral axis to extreme fiber *Bending Strength of AISI 4130 Steel (for tube dimension of Sec. 3.6.1 A) = 387.38 Nm
3.3 The Calculation
I= π/64 X (25.4^4 - 21.4^4)* = 10136.744mm^4 Sy = 480 N/mm^2 c = 12.7 Bending strength = SyI/c = (490 X 10136.744)/12.7 = 391.1 N-mm.
4.0 Chassis Design
3.2 The selection In order to achieve a light weight chassis with the above mentioned rules the only way is to reduce the wall thickness of the members. Light weight roll cage is very important as to have a better acceleration the car should be as light as possible. After going through the design data books we arrived with certain materials which have yield strength of above 600 MPa. After surveying the market availability in a tubular cross section pipe with the required properties we arrived at an optimized selection of material shown below.Out of the above mentioned materials AISI 4130 is the best suitable as it gives the minimum wall thickness as it has very high yield strength, as it is very expensive. The other options were SAE 106B and AISI 4130. The finalization was done with AISI 4130 as it is cheaper and also a less wall thickness can be achieved with it.
FIG(2)Basic views of chassis
FIG(3)Side view of chassis
rear, side impact and roll over were carried out in ANSYS for chassis analysis. 6.0 Ergonomics
FIG (4) Finalized design of chassis
For a comfortable ride, ergonomics plays an important role in the chassis design of the car. The ergonomic parameters are set after making a prototype prior to final manufacturing off the chassis . the prototype made with PVC pipe can be seen in fig 9.3 the driver sits in the prototype and checks the comfort as well as the safety rules meet or not e.g. 3 inch from all the body part to the chassis,6 inch between head and RHO.
The chassis finalized design can be seen from the figure above. The finalization was done after making three different designs and testing as well as light weight and ergonomics. 5.0 Roll cage analysis
FIG(7) Prototype with PVC pipe.
FIG(5)Chassis Roll over test: max. stress – 306 N/mm2 FOS = 1.7
FIG(6) Chassis Side impact test: max. stress – 362 N/mm2 FOS = 1.43
As per the yield strength of material selected the F.O.S. was calculated and the loading result can be seen in the figures. Loading conditions for front,
Fig(8) The actual car after farbrication.
The overall weight reduction in chassis due to the optimized material selection is the mass of the rollcage reduced to 40KGS which otherwise would have been 68KG if we directly selected the material AISI 4130. Through this paper we have tried to produce a clear understanding towards the fabrication of a baja buggy chasis. Our aim was to provide a basic understanding towards fabrication of the rollcage, from the designing phase to the fabrication of the chassis. It is of atmost imporatance to fabricate a chasis that is light in weight but also stands strong against most possible accidents keeping the driver safe. We also urge our readers to try and achieve the maximum safety and prioritise safety over other parameters. .
References  Baja sae rule book  Design of machine element by v.b bhandari  Vehicle Dynamics Theory Application[book] / auth. Reza N. Jazar
Fundamentals Of Vehicle Dynamics[book] / auth. by Thomas Gillespie.  Race Car Vehicle Dynamics[book] / auth. Miliken And Miliken  Paper #: Lawrence m Patrick,” Forces on the Human Body in Simulated Crashes,” 650961  Paper #: v.m mundada,” Development of 4Wheel Drive Utility Vehicle for Off-Road and Military Application”, 962558
 Thornton R. "Design Considerations for an Electric Car," SAE Technical Paper 700020, 1970, doi:10.4271/700020.
 Bradley L. and Carpenter, M., "Off Track Frame and Suspension Tuning (FAST)," SAE Technical Paper 942535, 1994, doi:10.4271/942535  Lanzavecchia, M. and Radice, P., "Road Vehicle Robust Design: Chassis and Suspension Tolerances Impact on the Handling and Stability
Behaviour," SAE Technical Paper 2008-01-0710, 2008, doi:10.4271/2008-01-0710