Reimplement tyre model to use separate longitudinal/lateral formulas, also use pacejka94

game/physics/pacejka.odin

@@ -1,22 +1,93 @@
+// https://www.edy.es/dev/docs/pacejka-94-parameters-explained-a-comprehensive-guide/
 package physics
 
 import "core:math"
 
-Pacejka96_Params :: [11]f32
+Pacejka94_Longitudinal_Params :: [14]f32
+Pacejka94_Lateral_Params :: [18]f32
 
-DEFAULT_PACEJKA96_PARAMS :: Pacejka96_Params{1.45, -150, 1500, 0, 400, -0.4, 0, 0, 0, 0, 0}
+PACEJKA94_LONGITUDINAL_PEAK_X :: 6.24
+PACEJKA94_LONGITUDINAL_PARAMS :: Pacejka94_Longitudinal_Params {
+	1.5,
+	0,
+	1100,
+	0,
+	300,
+	0,
+	0,
+	0,
+	-2,
+	0,
+	0,
+	0,
+	0,
+	0,
+}
+
+
+PACEJKA94_LATERAL_PEAK_X :: 6.26
+PACEJKA94_LATERAL_PARAMS :: Pacejka94_Lateral_Params {
+	1.4,
+	0,
+	1100,
+	1100,
+	10,
+	0,
+	0,
+	-2,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+}
 
 // X is slip ratio percentage [-100, 100] or slip angle in degrees, where positive angle is turning left
 // Output is the friction coefficient
-pacejka_96 :: proc(b: Pacejka96_Params, x: f32, f_z: f32, s_v: f32 = 0) -> f32 {
+pacejka_94_longitudinal :: proc(
+	b: Pacejka94_Longitudinal_Params,
+	x: f32,
+	f_z: f32,
+	s_v: f32 = 0,
+) -> f32 {
+	f_z_sq := f_z * f_z
+
 	C := b[0]
 	D := (b[1] * f_z + b[2]) * f_z
-	B := ((b[3] * f_z * f_z + b[4] * f_z) * math.exp(-b[5] * f_z)) / (C * D)
+	BCD := (b[3] * f_z_sq + b[4] * f_z) * math.exp(-b[5] * f_z)
-	E := (b[6] * f_z * f_z + b[7] * f_z + b[8])
+	B := BCD / (C * D)
-	s_h := b[9] * f_z + b[10]
+	H := b[9] * f_z + b[10]
+	E := (b[6] * f_z_sq + b[7] * f_z + b[8]) * (1.0 - b[13] * math.sign(x + H))
+	V := b[11] * f_z + b[12]
+	Bx1 := B * (x + H)
 
-	X := x + s_h
+	F := D * math.sin(C * math.atan(Bx1 - E * (Bx1 - math.atan(Bx1)))) + V
-	y := D * math.sin(C * math.atan(B * X - E * (B * X - math.atan(B * X))))
+
-	Y := y + s_v
+	return F / (f_z * 1000)
-	return Y / (f_z * 1000)
+}
+
+pacejka_94_lateral :: proc(
+	a: Pacejka94_Lateral_Params,
+	slip_angle: f32,
+	f_z: f32,
+	camber_angle: f32,
+) -> f32 {
+	camber_angle_sq := camber_angle * camber_angle
+
+	C := a[0]
+	D := f_z * (a[1] * f_z + a[2]) * (1.0 - a[15] * camber_angle_sq)
+	BCD := a[3] * math.sin(math.atan(f_z / a[4]) * 2.0) * (1.0 - a[5] * abs(camber_angle))
+	B := BCD / (C * D)
+	H := a[8] * f_z + a[9] + a[10] * camber_angle
+	E := (a[6] * f_z + a[7]) * (1.0 - (a[16] * camber_angle + a[17]) * math.sign(slip_angle + H))
+	V := a[11] * f_z + a[12] + (a[13] * f_z + a[14]) * camber_angle * f_z
+	Bx1 := B * (slip_angle + H)
+
+	F := D * math.sin(C * math.atan(Bx1 - E * (Bx1 - math.atan(Bx1)))) + V
+	return F / (f_z * 1000)
 }

game/physics/simulation.odin

@@ -789,45 +789,15 @@ pgs_solve_suspension :: proc(
 					// 	body_vel_at_contact_patch + (v.radius * v.w * forward)
 
 					slip_ratio :=
-						ground_vel == 0 ? 0 : clamp(wheel_spin_vel / ground_vel - 1, -1, 1)
+						ground_vel == 0 ? 0 : clamp(wheel_spin_vel / ground_vel - 1, -1, 1) * 100.0
 					slip_angle :=
 						lg.angle_between(forward, body_vel_at_contact_patch) * math.DEG_PER_RAD
 
-					SLIP_RATIO_PARAMS :: Pacejka96_Params {
-						1.7,
-						-150,
-						1500,
-						0,
-						700,
-						-0.8,
-						0,
-						0,
-						0,
-						0,
-						0,
-					}
-
-					SLIP_ANGLE_PARAMS :: Pacejka96_Params {
-						1.6,
-						-150,
-						1500,
-						0,
-						229,
-						-0.4,
-						0,
-						0,
-						0,
-						0,
-						0,
-					}
-
-					OPTIMAL_SLIP_RATIO :: f32(0.0078)
-					OPTIMAL_SLIP_ANGLE :: f32(5.5)
 					MAX_SLIP_LEN :: f32(2.0)
 
 					slip_vec := Vec2 {
-						slip_angle / OPTIMAL_SLIP_ANGLE / MAX_SLIP_LEN,
+						slip_angle / PACEJKA94_LATERAL_PEAK_X / MAX_SLIP_LEN,
-						slip_ratio / OPTIMAL_SLIP_RATIO / MAX_SLIP_LEN,
+						slip_ratio / PACEJKA94_LONGITUDINAL_PEAK_X / MAX_SLIP_LEN,
 					}
 
 					slip_len := lg.length(slip_vec)
@@ -838,19 +808,20 @@ pgs_solve_suspension :: proc(
 
 					long_friction :=
 						abs(
-							pacejka_96(
+							pacejka_94_longitudinal(
-								SLIP_RATIO_PARAMS,
+								PACEJKA94_LONGITUDINAL_PARAMS,
-								slip_ratio * 100,
+								slip_ratio,
 								max(abs(v.spring_impulse), 0.001) * inv_dt * 0.001,
 							),
 						) *
 						abs(slip_vec.y)
 					lat_friction :=
 						abs(
-							pacejka_96(
+							pacejka_94_lateral(
-								SLIP_ANGLE_PARAMS,
+								PACEJKA94_LATERAL_PARAMS,
 								slip_angle,
 								max(abs(v.spring_impulse), 0.001) * inv_dt * 0.001,
+								0.0,
 							),
 						) *
 						abs(slip_vec.x)