### Yaw Rate Gain Analysis Setup in Python Source: https://context7.com/ericcabrol/vehicledynamics/llms.txt Initializes parameters for yaw rate gain analysis. This snippet sets up vehicle parameters like wheelbase and understeer gradient. ```python import numpy as np import matplotlib.pyplot as plt # Vehicle parameters L = 2.8 # Wheelbase (m) K = 0.0035 # Understeer gradient (rad/(m/s^2)) ``` -------------------------------- ### Initialize Environment Source: https://github.com/ericcabrol/vehicledynamics/blob/master/Pacejka_part1.ipynb Imports necessary libraries for plotting and mathematical calculations. ```python %matplotlib inline import matplotlib.pyplot as plt from math import sin, atan import numpy as np ``` -------------------------------- ### Bicycle Model Implementation in Python Source: https://context7.com/ericcabrol/vehicledynamics/llms.txt Calculates steady-state cornering parameters using the bicycle model. Requires vehicle parameters like wheelbase, mass, and cornering stiffness. ```python import math import numpy as np import matplotlib.pyplot as plt # Vehicle parameters a = 1.2 # Distance from CoG to front axle (m) b = 1.6 # Distance from CoG to rear axle (m) m = 1500 # Vehicle mass (kg) osr = 15 # Overall steering ratio L = a + b # Wheelbase (m) # Cornering stiffness values (N/rad) Cf = 120000 # Front axle cornering stiffness Cr = 180000 # Rear axle cornering stiffness # Maneuver data R = 80 # Turn radius (m) V = 20 # Vehicle speed (m/s) # Constants rad2deg = 180 / math.pi g = 9.81 # m/s^2 # Calculate mass distribution from static balance mf = m * b / L # Mass on front axle mr = m * a / L # Mass on rear axle # Calculate lateral acceleration ay = V**2 / R # Calculate Ackermann angle (kinematic steering angle) delta_ack = math.atan(L / R) # Calculate slip angles Fyf = mf * ay # Lateral force on front axle (N) Fyr = mr * ay # Lateral force on rear axle (N) alpha_f = Fyf / Cf # Front slip angle (rad) alpha_r = Fyr / Cr # Rear slip angle (rad) # Calculate understeer gradient K = mf / Cf - mr / Cr # rad/(m/s^2) # Calculate characteristic speed (for understeering vehicle) V_ch = math.sqrt(L / K) if K > 0 else None # Calculate static margin e = (a * Cf - b * Cr) / (Cf + Cr) static_margin = e / L print(f"Lateral acceleration: {ay:.2f} m/s^2 ({ay/g:.2f} g)") print(f"Ackermann angle: {delta_ack * rad2deg:.2f}°") print(f"Front slip angle: {alpha_f * rad2deg:.3f}°") print(f"Rear slip angle: {alpha_r * rad2deg:.3f}°") print(f"Understeer gradient: {K * rad2deg:.2f} °/(m/s^2) = {K * rad2deg * g:.2f} °/g") print(f"Characteristic speed: {V_ch:.1f} m/s ({V_ch * 3.6:.1f} km/h)") print(f"Static margin: {static_margin * 100:.2f}%") # Output: # Lateral acceleration: 5.00 m/s^2 (0.51 g) # Ackermann angle: 2.00° # Front slip angle: 2.045° # Rear slip angle: 1.024° # Understeer gradient: 0.20 °/(m/s^2) = 2.01 °/g # Characteristic speed: 28.0 m/s (100.8 km/h) # Static margin: -17.14% ``` -------------------------------- ### Analyze Pacejka parameter sensitivity Source: https://context7.com/ericcabrol/vehicledynamics/llms.txt Visualizes how variations in parameters B, C, D, and E affect the tire force curve. ```python from math import sin, atan import numpy as np import matplotlib.pyplot as plt def pacejka(slip, B, C, D, E): return D * sin(C * atan(B * slip - E * (B * slip - atan(B * slip)))) # Base parameters B_base, C_base, D_base, E_base = 0.171, 1.69, 4236, 0.619 slip = np.linspace(0, 100, 200) fig, axes = plt.subplots(2, 2, figsize=(14, 10)) # Effect of D (peak factor) - controls maximum force ax = axes[0, 0] for D_val in [3500, 4000, 4500, 5000]: Fx = [pacejka(s, B_base, C_base, D_val, E_base) for s in slip] ax.plot(slip, Fx, label=f'D = {D_val}') ax.set_xlabel('Slip (%)') ax.set_ylabel('Force (N)') ax.set_title('Effect of Peak Factor D\n(Higher D = Higher maximum force)') ax.legend() ax.grid(True) # Effect of C (shape factor) - controls peak sharpness ax = axes[0, 1] for C_val in [1.3, 1.5, 1.7, 2.0]: Fx = [pacejka(s, B_base, C_val, D_base, E_base) for s in slip] ax.plot(slip, Fx, label=f'C = {C_val}') ax.set_xlabel('Slip (%)') ax.set_ylabel('Force (N)') ax.set_title('Effect of Shape Factor C\n(Higher C = Sharper peak, faster force decay)') ax.legend() ax.grid(True) # Effect of E (curvature factor) - controls post-peak behavior ax = axes[1, 0] for E_val in [-1.0, 0.0, 0.5, 0.9]: Fx = [pacejka(s, B_base, C_base, D_base, E_val) for s in slip] ax.plot(slip, Fx, label=f'E = {E_val}') ax.set_xlabel('Slip (%)') ax.set_ylabel('Force (N)') ax.set_title('Effect of Curvature Factor E\n(Higher E = Flatter curve, E must be < 1)') ax.legend() ax.grid(True) ``` -------------------------------- ### Visualize Pacejka Stiffness Factor B Source: https://context7.com/ericcabrol/vehicledynamics/llms.txt Plots the effect of the stiffness factor B on tire force generation using the Pacejka model. ```python ax = axes[1, 1] for B_val in [0.12, 0.17, 0.22, 0.30]: Fx = [pacejka(s, B_base, C_base, D_base, E_base) for s in slip] ax.plot(slip[:30], [pacejka(s, B_val, C_base, D_base, E_base) for s in slip[:30]], label=f'B = {B_val}') ax.set_xlabel('Slip (%)') ax.set_ylabel('Force (N)') ax.set_title('Effect of Stiffness Factor B\n(Higher B = Steeper initial slope)') ax.legend() ax.grid(True) plt.tight_layout() plt.show() ``` -------------------------------- ### Configure Plotting Data Source: https://github.com/ericcabrol/vehicledynamics/blob/master/Pacejka_part1.ipynb Sets up the slip ratio range and matplotlib figure dimensions. ```python num_points=100 X = np.linspace(0,100,100) plt.rcParams["figure.figsize"] = (8,6) # set fig size for matplotlib ``` -------------------------------- ### Implement Pacejka Magic Formula Source: https://context7.com/ericcabrol/vehicledynamics/llms.txt Calculates longitudinal tire force using the 1987 Pacejka model and visualizes the force-slip curve. ```python from math import sin, atan import numpy as np import matplotlib.pyplot as plt def pacejka_tire_force(slip, B, C, D, E): """ Calculate tire force using Pacejka Magic Formula. Parameters: - slip: Slip ratio (%) for longitudinal, or slip angle (deg) for lateral - B: Stiffness factor (controls initial slope) - C: Shape factor (controls peak sharpness) - D: Peak factor (maximum force value) - E: Curvature factor (controls post-peak behavior, must be < 1) Returns: - Force in Newtons """ return D * sin(C * atan(B * slip - E * (B * slip - atan(B * slip)))) # Tire parameters for Fz = 4 kN (from Pacejka 1987 paper) B = 0.171 # Stiffness factor C = 1.69 # Shape factor D = 4236 # Peak factor (N) - equals Fz * mu_max E = 0.619 # Curvature factor # Calculate longitudinal force vs slip ratio slip_ratio = np.linspace(0, 100, 200) # Slip ratio in % Fx = np.array([pacejka_tire_force(s, B, C, D, E) for s in slip_ratio]) # Find peak force and corresponding slip peak_idx = np.argmax(Fx) peak_slip = slip_ratio[peak_idx] peak_force = Fx[peak_idx] print(f"Peak longitudinal force: {peak_force:.0f} N at {peak_slip:.1f}% slip") print(f"Friction coefficient at peak: {peak_force / 4000:.3f}") plt.figure(figsize=(10, 6)) plt.plot(slip_ratio, Fx, 'b-', linewidth=2) plt.axhline(y=D, color='orange', linestyle='--', label=f'Peak factor D = {D} N') plt.scatter([peak_slip], [peak_force], color='red', s=100, zorder=5, label=f'Peak at {peak_slip:.1f}%') plt.xlabel('Slip Ratio (%)') plt.ylabel('Longitudinal Force Fx (N)') plt.title('Pacejka Magic Formula - Longitudinal Tire Force') plt.legend() plt.grid(True) plt.show() ``` -------------------------------- ### Calculate Basic Vehicle Kinematics Source: https://github.com/ericcabrol/vehicledynamics/blob/master/bicycle_model.ipynb Calculates and prints the lateral acceleration and steering angles based on vehicle dimensions and maneuver data. Requires Python 3.6+ for f-string formatting. ```python %matplotlib inline import matplotlib.pyplot as plt import math import numpy as np # Vehicle data a = 1.2 # m b = 1.6 # m m = 1500 # kg osr = 15 L = a + b # m # Manoeuver data R = 80 # m V = 5 # m/s rad2deg = 180/math.pi g = 9.81 # m/s^2 ay = V**2 / R δ_ack = math.atan(L/R) # Caution : f-string used here (only with Python 3.6+ - Switch to the older format function if required) print() print(f"{'Lateral acceleration':40} = {ay:.2f} m/s^2") print(f"{'Ackermann angle at the wheel':40} = {δ_ack:.3f} rad.") print(f"{'Angle at the steering wheel':40} = {δ_ack*osr*rad2deg:.1f} deg.") ``` -------------------------------- ### Visualize Stiffness Factor B Variation Source: https://github.com/ericcabrol/vehicledynamics/blob/master/Pacejka_part1.ipynb Plots the longitudinal force Fx for varying values of B to observe changes in curve stiffness at low slip ratios. ```python E=0.619 # reset plt.figure() i=0 for B in np.arange(0.12,0.33,0.03): i+=0.1 plt.plot(X,np.vectorize(F)(X),color=(0.,0.,0.,i)); plt.gca().annotate('increasing B', xy=(5,3000), xytext=(7,2000),arrowprops=dict(facecolor='black')); plt.xlim(0,15) plt.title('Variation of Fx with stiffness factor B'); B=0.171 # reset ``` -------------------------------- ### Visualize Peak Factor D Variation Source: https://github.com/ericcabrol/vehicledynamics/blob/master/Pacejka_part1.ipynb Demonstrates how varying the peak factor D affects the maximum force without changing the curve shape. ```python plt.figure() i=0 for D in np.arange(3500,5300,300): i+=0.1 plt.plot(X,np.vectorize(F)(X),color=(0.,0.,1.,i)); plt.gca().annotate('increasing D', xy=(60,5000), xytext=(60,4000),arrowprops=dict(facecolor='black')); plt.title('Variation of Fx with peak factor D'); D = 4236 # reset ``` -------------------------------- ### Define Pacejka Formula Source: https://github.com/ericcabrol/vehicledynamics/blob/master/Pacejka_part1.ipynb Sets the tire parameters and defines the function F(x) based on the original Pacejka paper. ```python # Definition of Pacejka parameters # X : longitudinal slip # B : stiffness factor # C : shape factor # D : peak factor # E : curvature factor B = 0.171 C = 1.69 D = 4236 E = 0.619 def F(x): return(D * sin(C * atan(B*x - E*(B*x - atan(B*x))))) ``` -------------------------------- ### Demonstrate Invalid Curvature Factor Source: https://github.com/ericcabrol/vehicledynamics/blob/master/Pacejka_part1.ipynb Shows the physical impossibility of E > 1, resulting in negative tire forces at high slip. ```python E=1.15 # impossible value plt.figure() plt.plot(X,np.vectorize(F)(X)); plt.plot(X,np.linspace(0,0,num_points),linestyle='--',color='red'); plt.gca().annotate('Nobody wants this to happen on a car :)', xy=(65,-1000), xytext=(30,-2000),arrowprops=dict(facecolor='black')); plt.title('Why E > 1 is impossible'); ``` -------------------------------- ### Lateral Acceleration Gain Calculation in Python Source: https://context7.com/ericcabrol/vehicledynamics/llms.txt Calculates and plots the vehicle's lateral acceleration gain per steering angle. Useful for tuning ESC systems. Requires vehicle parameters and speed. ```python import numpy as np import matplotlib.pyplot as plt # Vehicle parameters (from bicycle model) L = 2.8 # Wheelbase (m) K = 0.0035 # Understeer gradient (rad/(m/s^2)) osr = 15 # Overall steering ratio g = 9.81 # m/s^2 rad2deg = 180 / 3.14159 # Calculate lateral acceleration gain at specific speed V = 20 # m/s lateral_accel_gain = (V**2 / L) / (1 + K * V**2 / L) print(f"At V = {V} m/s ({V * 3.6:.0f} km/h):") print(f"Lateral acceleration gain: {lateral_accel_gain / rad2deg:.3f} (m/s^2)/°") print(f"Lateral acceleration for 100° at steering wheel: {lateral_accel_gain / rad2deg / g * 100 / osr:.3f} g") # Plot gain variation with speed V_range = np.linspace(5, 50, 100) ay_gain = (V_range**2 / L) / (1 + K * V_range**2 / L) ay_per_100deg = ay_gain / rad2deg / g * 100 / osr plt.figure(figsize=(10, 5)) plt.plot(V_range * 3.6, ay_per_100deg) plt.xlabel('Speed (km/h)') plt.ylabel('Lateral acceleration (g) for 100° steering') plt.title('Lateral Acceleration Gain vs Speed') plt.grid(True) plt.show() ``` -------------------------------- ### Visualize Curvature Factor E Variation Source: https://github.com/ericcabrol/vehicledynamics/blob/master/Pacejka_part1.ipynb Illustrates the effect of the curvature factor E on the flatness of the force curve. ```python plt.figure() i=0 for E in np.arange(-2.0,1.5,0.5): i+=0.1 plt.plot(X,np.vectorize(F)(X),color=(1.,0.,1.,i)); plt.gca().annotate('increasing E', xy=(80,4000), xytext=(80,3000),arrowprops=dict(facecolor='black')); plt.title('Variation of Fx with curvature factor E'); E=0.619 # reset ``` -------------------------------- ### Calculate static margin Source: https://github.com/ericcabrol/vehicledynamics/blob/master/bicycle_model.ipynb Computes the static margin based on the distance from the center of gravity to the neutral steer point. ```python distance_CoG_to_neutral_steer_point = (a*Cf-b*Cr)/(Cf+Cr) print() print(f"{'Static margin':40} = {distance_CoG_to_neutral_steer_point/L*100 :.2f} %") ``` -------------------------------- ### Calculate Understeer Gradient Source: https://github.com/ericcabrol/vehicledynamics/blob/master/bicycle_model.ipynb Calculates the understeer gradient in degrees per (m/s^2) and degrees per g, both at the wheel and at the steering wheel. This metric indicates the vehicle's tendency to understeer or oversteer. ```python K = mf/Cf - mr/Cr print() print(f"{'Understeer gradient at the wheel':40} = {K * rad2deg :.2f} °/(m/s^2)") print(f"{'':40} = {K * rad2deg * g :.2f} °/g") print() print(f"{'Understeer gradient at the steering wheel':45} = {K * rad2deg * osr :.2f} °/(m/s^2)") print(f"{'':45} = {K * rad2deg * g * osr :.2f} °/g") ``` -------------------------------- ### Analyze Vehicle Handling Characteristics Source: https://context7.com/ericcabrol/vehicledynamics/llms.txt Calculates understeer gradient, critical speed, and static margin to classify vehicle behavior as understeer, oversteer, or neutral. ```python import math import numpy as np import matplotlib.pyplot as plt def analyze_vehicle_handling(name, m, a, b, Cf, Cr): """ Analyze handling characteristics of a vehicle configuration. Parameters: - name: Vehicle configuration name - m: Total mass (kg) - a: Distance from CoG to front axle (m) - b: Distance from CoG to rear axle (m) - Cf: Front axle cornering stiffness (N/rad) - Cr: Rear axle cornering stiffness (N/rad) Returns: - Dictionary with handling parameters """ L = a + b mf = m * b / L mr = m * a / L K = mf / Cf - mr / Cr # Understeer gradient if K > 0: behavior = "Understeer" critical_speed = math.sqrt(L / K) elif K < 0: behavior = "Oversteer" critical_speed = math.sqrt(L / abs(K)) else: behavior = "Neutral" critical_speed = float('inf') static_margin = (a * Cf - b * Cr) / ((Cf + Cr) * L) return { 'name': name, 'behavior': behavior, 'K': K, 'K_deg_per_g': K * 180 / math.pi * 9.81, 'critical_speed_kmh': critical_speed * 3.6, 'static_margin_pct': static_margin * 100 } # Define different vehicle configurations vehicles = [ # Understeer: front-heavy, soft front tires analyze_vehicle_handling("Front-heavy understeer", 1500, 1.2, 1.6, 120000, 180000), # Neutral steer analyze_vehicle_handling("Neutral steer", 1500, 1.4, 1.4, 150000, 150000), # Oversteer: rear-heavy, soft rear tires analyze_vehicle_handling("Rear-heavy oversteer", 1500, 1.6, 1.2, 180000, 120000), ] print("Vehicle Handling Comparison") print("=" * 70) for v in vehicles: print(f"\n{v['name']}:") print(f" Behavior: {v['behavior']}") print(f" Understeer gradient: {v['K_deg_per_g']:.2f} °/g") print(f" {'Characteristic' if v['behavior'] == 'Understeer' else 'Critical'} speed: {v['critical_speed_kmh']:.1f} km/h") print(f" Static margin: {v['static_margin_pct']:.2f}%") ``` -------------------------------- ### Visualize Shape Factor C Variation Source: https://github.com/ericcabrol/vehicledynamics/blob/master/Pacejka_part1.ipynb Shows how the shape factor C influences the peakiness of the tire force curve. ```python plt.figure() i=0 for C in np.arange(1.5,2.1,0.1): i+=0.1 plt.plot(X,np.vectorize(F)(X),color=(1.,0.,0.,i)); plt.gca().annotate('increasing C', xy=(30,500), xytext=(40,1500),arrowprops=dict(facecolor='black')); plt.title('Variation of Fx with shape factor C'); C=1.69 # reset ``` -------------------------------- ### Plot lateral acceleration gain Source: https://github.com/ericcabrol/vehicledynamics/blob/master/bicycle_model.ipynb Visualizes the variation of lateral acceleration gain with respect to vehicle speed. ```python V1 = np.linspace(10, 40, 100) plt.plot(V1, (V1**2/L) / (1 + K*V1**2/L) / rad2deg / g * 100 / osr, label='ay for 100° SW'); plt.legend(); plt.xlabel('V (m/s)'); plt.ylabel('ay (g)'); ``` -------------------------------- ### Calculate yaw rate gain Source: https://context7.com/ericcabrol/vehicledynamics/llms.txt Computes and plots the yaw rate gain as a function of vehicle speed, identifying the characteristic speed. ```python V_range = np.linspace(5, 50, 100) yaw_rate_gain = (V_range / L) / (1 + K * V_range**2 / L) # Find characteristic speed (where gain is maximum) V_ch = np.sqrt(L / K) max_gain = (V_ch / L) / (1 + K * V_ch**2 / L) print(f"Characteristic speed: {V_ch:.1f} m/s ({V_ch * 3.6:.1f} km/h)") print(f"Maximum yaw rate gain: {max_gain:.2f} s^-1") plt.figure(figsize=(10, 5)) plt.plot(V_range * 3.6, yaw_rate_gain, label='Yaw rate gain') plt.axvline(x=V_ch * 3.6, color='r', linestyle='--', label=f'Characteristic speed = {V_ch * 3.6:.0f} km/h') plt.xlabel('Speed (km/h)') plt.ylabel('Yaw rate gain (r/δ) [1/s]') plt.title('Yaw Rate Gain vs Speed') plt.legend() plt.grid(True) plt.show() ``` -------------------------------- ### Determine Characteristic or Critical Speed Source: https://github.com/ericcabrol/vehicledynamics/blob/master/bicycle_model.ipynb Calculates and prints the characteristic speed (for understeer) or critical speed (for oversteer) in m/s and km/h. This speed is a stability indicator for the vehicle. ```python print() if K>=0: print(f"{'Characteristic speed':40} = {math.sqrt(L/K):.1f} m/s") print(f"{'':40} = {math.sqrt(L/K) * 3.6:.1f} km/h") else: print(f"{'Critical speed':40} = {math.sqrt(L/abs(K)):.1f} m/s") print(f"{'':40} = {math.sqrt(L/abs(K)) * 3.6:.1f} km/h") ``` -------------------------------- ### Calculate and plot yaw rate gain Source: https://github.com/ericcabrol/vehicledynamics/blob/master/bicycle_model.ipynb Computes the yaw rate gain and plots its variation against speed to identify the characteristic speed. ```python yaw_rate_gain = (V/L) / (1 + K*V**2/L) print() print(f"{'Yaw rate gain':40} = {yaw_rate_gain :.2f} s^-1") print() # Let's plot this gain variation with speed V1 = np.linspace(10, 40, 100) plt.plot(V1, (V1/L) / (1 + K*V1**2/L), label='yaw rate gain'); plt.legend(); plt.xlabel('V (m/s)'); plt.ylabel(r'$r\ /\ \delta$'); ``` -------------------------------- ### Plot Base Pacejka Curve Source: https://github.com/ericcabrol/vehicledynamics/blob/master/Pacejka_part1.ipynb Visualizes the longitudinal force curve with a reference line for the peak factor D. ```python plt.plot(X,np.vectorize(F)(X)); # horizontal line at the max value for visualization purpose only plt.plot(X,np.linspace(D,D,num_points),linestyle='--',color='orange'); ``` -------------------------------- ### Calculate Lateral Acceleration Gain Source: https://github.com/ericcabrol/vehicledynamics/blob/master/bicycle_model.ipynb Calculates the lateral acceleration gain, which represents the ratio of lateral acceleration to steering wheel angle. It's expressed in (m/s^2)/° and g/°. Also calculates the lateral acceleration for a 100° steering wheel input. ```python lateral_accel_gain = (V**2/L) / (1 + K*V**2/L) print() print(f"{'Lateral acceleration gain':40} = {lateral_accel_gain / rad2deg :.2f} (m/s^2)/°") print(f"{'':40} = {lateral_accel_gain / rad2deg / g :.3f} g/°") print() print(f"{'Lateral acceleration for 100° at the SW':40} = {lateral_accel_gain / rad2deg / g * 100 / osr :.3f} g") ``` -------------------------------- ### Calculate Slip Angles and Forces at Higher Speed Source: https://github.com/ericcabrol/vehicledynamics/blob/master/bicycle_model.ipynb Calculates lateral forces and slip angles at front and rear axles for a vehicle at a higher speed, considering cornering stiffness. Assumes axle properties are aggregated at the axle center. ```python Cf = 120000 # N/rad Cr = 180000 # N/rad # From the static balance we have mf = m * b / L mr = m * a / L # Let's increase the speed to reach a non-negligible lateral acceleration V = 20 # m/s # Recompute ay = V**2 / R # So Fyf = mf * ay Fyr = mr * ay # The slip angles at the front and rear axle are αf = Fyf / Cf αr = Fyr / Cr print() print(f"{'Lateral acceleration':40} = {ay:.2f} m/s^2") print(f"{'Mass on the front axle':40} = {mf:.1f} kg") print(f"{'Mass on the rear axle':40} = {mr:.1f} kg") print(f"{'Lateral force on the front axle':40} = {Fyf:.0f} N") print(f"{'Lateral force on the rear axle':40} = {Fyr:.0f} N") print(f"{'Slip angle at the front axle':40} = {αf:.3f} rad") print(f"{'Slip angle at the rear axle':40} = {αr:.3f} rad") ``` === COMPLETE CONTENT === This response contains all available snippets from this library. No additional content exists. Do not make further requests.