Design2.py

import math

''' For designinig chassis we have to consider bending stiffness(For side members) and torsional stiffness (For cross members)
1st design for calculating dimensions of side members'''
Weight = 1500 # kg considering average gross weight of vehicle for designing a chassis excluding passenger weight
Payload = 500 # considering payload of 500 kg for safety
Passengers = float(input("Enter the number of passengers = ") or "5")
Battery_weight = float(input("Enter the battery weight in kg = ") or "270")
Force=(Weight+Payload+75*Passengers+Battery_weight)*9.81 # N Force acting on side members
Force_on_each_side_member = Force/2 

if Passengers == 1 or Passengers == 2:
    wheelBase=1800
elif Passengers == 3 or Passengers == 4:
    wheelBase=2450
else:
    wheelBase=2900

# Bending_Stiffness is in N/mm (For chassis to be safe or avoid bending it should have bending stiffness more than 3 kN/mm)
Bending_Stiffness = 3500

# Mpa Considering material High carbon steel, typical application for making chassis
Modulus_of_Elasticity = 200000


# Where 'a' is equal to moment of inertia considering Hollow rectangular section
a = Bending_Stiffness*pow(wheelBase, 3)/(48*Modulus_of_Elasticity) # moment of inertia = (bending stiffness*l^3)/48*E
print("Minimum value of moment of inertia to sustain bending load = ", a)


def trialAndError():
    global W, w, H, h
    min_lhs = a   # Minimum value for moment of inertia satisfying the value of 'a' so that side members can susutain bending load
    max_lhs = 20000000
    min_w = 50
    max_w = 140
    min_t = 5
    max_t = 20

    # Start with middle values
    w = min_w 
    t = min_t 
    lhs = ((w * pow(1.5*w, 3))/12) - (((w-2*t)*pow((1.5*w-2*t), 3))/12)

    while lhs <= min_lhs or lhs >= max_lhs:
        if lhs <= min_lhs:
            # If lhs is too small, increase w and t
            w += 1
            t += 0.1
        else:
            # If lhs is too large, decrease w and t
            w -= 1
            t -= 0.1
        lhs = ((w * pow(1.5*w, 3))/12) - (((w-2*t)*pow((1.5*w-2*t), 3))/12)

    print(f"w = {w:.2f}, t = {t:.2f}")
    H = round(1.5*w)
    h = round(H-2*t)
    W = round(w)
    w = round(W-2*t)

trialAndError()
print(" Dimensions of rectangular cross section to draw side members ")
print("Width of outer rectangle = ", W, "mm")
print("Width of inner rectangle = ", w, "mm")
print("Height of outer rectangle = ", H, "mm")
print("Height of inner rectangle = ", h, "mm")

# For dimensions of cross members

# We have to consider torsional stiffness with value greater than 4 kN m/deg for vehical to sustain torsional load
Torsional_Stiffness = 4500000  # N mm/deg
print("For cross member dimensions")
Front_Track = 1520
Length = Front_Track/2

# Torsional force acting on frame (force acting multiplied by perpendicular distance)
Torsional_Force = Force_on_each_side_member*Length
theta = Torsional_Force/Torsional_Stiffness

tan_theta = math.tan(theta*3.14/180)
x = tan_theta*Length  # Where x is half of the height of cross member
Height_of_the_cross_member = 2*x

Width_of_the_cross_member = Height_of_the_cross_member/1.5
print("Dimensions of cross members")
print("Width of outer rectangle of cross member = ",Width_of_the_cross_member, "mm")
print("Width of inner rectangle of cross member = ",Width_of_the_cross_member-10, "mm")
print("Height of outer cross member = ", Height_of_the_cross_member, "mm")
print("Height of inner cross member = ", Height_of_the_cross_member-10, "mm")
print("length of cross member = ", Front_Track-2*W, "mm")