fix: stick laterally on incline

Author: PenguinDevs

src/landvehicle/src/Client/Classes/Suspensions/WheelVehicleSuspensionClient.luau

@@ -101,6 +101,7 @@ function Suspension.new(vehicleObj: Model, config: WheelVehicleTypes.SuspensionC
 	-- self.force.RelativeTo = Enum.ActuatorRelativeTo.Attachment0
 	self.force.Force = Vector3.new(0, 0, 0)
 	self.force.Attachment0 = self.forceAttachment
+	self.force.Visible = true
 	self.force.Parent = self.forceAttachment
 	self._maid.relativeForce = self.force
 

src/landvehicle/src/Client/Classes/Suspensions/WheelVehicleSuspensionControllerClient.luau

@@ -120,19 +120,17 @@ end
 
 function SuspensionController.UpdateStepped(self: SuspensionController, deltaTimeSim: number)
 	-- Makeshift speedometer
-	-- print(self._vehicleObj.PrimaryPart.AssemblyLinearVelocity.Magnitude * (1 / 3.57) * 3.6, "km/h")
+	-- print((self._vehicleObj.PrimaryPart :: BasePart).AssemblyLinearVelocity.Magnitude * (1 / 3.57) * 3.6, "km/h")
 
 	for _, suspension in pairs(self._suspensions) do
 		suspension:UpdateStepped(deltaTimeSim)
 
 		-- NOTE: A very basic implementation to get the car moving.
-		if suspension.wheel then
-			local brakeInputScaled = self.brakeInput
-			if suspension.wheel.angularVelocity > 0 then
-				brakeInputScaled *= 6
-			end
-			suspension.wheel.baseTorque = (self.throttleInput - brakeInputScaled) * 20
+		local brakeInputScaled = self.brakeInput
+		if suspension.wheel.angularVelocity > 0 then
+			brakeInputScaled *= 6
 		end
+		suspension.wheel.baseTorque = (self.throttleInput - brakeInputScaled) * 20
 	end
 
 	for _, steeringSuspension in pairs(self._steeringSuspensions) do

src/landvehicle/src/Client/Classes/WheelVehicleClient.luau

@@ -275,6 +275,7 @@ function WheelVehicleClient:_createSuspensions()
 				wheelObj,
 				suspensionInstance._config.wheel,
 				WheelVehicleUtils:GetLinks(self._obj, suspension.position),
+				suspensionInstance.forceAttachment,
 				self._config.chassis.mass
 			)
 			suspensionInstance.wheel = wheelInstance

src/landvehicle/src/Client/Classes/Wheels/WheelVehiclePacejkaWheelClient.luau

@@ -3,6 +3,7 @@
 
 	See http://www-cdr.stanford.edu/dynamic/bywire/tires.pdf.
 	Used as reference for this implementation.
+	Note that this is a Pacejka '94 version model. Not '89.
 
 	TODO: Massive simplifications and optimisations are possible once everything is finalised.
 
@@ -25,13 +26,15 @@ local REALISTIC_GRAVITY = 35 -- 35 studs/s^2 -> 9.8 m/s^2
 local PI = math.pi
 local TWO_PI = PI * 2
 local sin = math.sin
+local tan = math.tan
 local atan = math.atan
 local atan2 = math.atan2
 local abs = math.abs
 local min = math.min
 local exp = math.exp
 local deg = math.deg
 local sign = math.sign
+local max = math.max
 local euler = exp(1)
 
 local PacejkaWheel = setmetatable({}, WheelVehicleWheelClient)
@@ -40,7 +43,7 @@ PacejkaWheel.__index = PacejkaWheel
 
 export type PacejkaWheel =
 	typeof(setmetatable(
-		{} :: { _vehicleMass: number, _torqueToCarForceRatio: number },
+		{} :: { _vehicleMass: number, _torqueToCarForceRatio: number, _wheelInertia: number },
 		{} :: typeof({ __index = PacejkaWheel })
 	))
 	& WheelVehicleWheelClient.Wheel
@@ -49,9 +52,10 @@ function PacejkaWheel.new(
 	wheelObj: BasePart,
 	wheelConfig: WheelVehicleTypes.WheelConfig,
 	links: WheelVehicleUtils.Links,
+	_forceAttachment: Attachment,
 	_vehicleMass: number
 ): PacejkaWheel
-	local self = setmetatable(WheelVehicleWheelClient.new(wheelObj, wheelConfig, links), PacejkaWheel)
+	local self = setmetatable(WheelVehicleWheelClient.new(wheelObj, wheelConfig, links, _forceAttachment), PacejkaWheel)
 
 	self._vehicleMass = _vehicleMass
 
@@ -90,9 +94,9 @@ end
 function PacejkaWheel.SetConstants(self: PacejkaWheel)
 	WheelVehicleWheelClient.SetConstants(self)
 
-	local wheelInertia = 1 / 2 * self.mass * self.radius ^ 2
-	self._torqueToCarForceRatio = (wheelInertia / self.radius ^ 2)
-		/ (self._vehicleMass + wheelInertia / self.radius ^ 2)
+	self._wheelInertia = 1 / 2 * self.mass * self.radius ^ 2
+	self._torqueToCarForceRatio = (self._wheelInertia / self.radius ^ 2)
+		/ (self._vehicleMass + self._wheelInertia / self.radius ^ 2)
 end
 
 function PacejkaWheel.UpdateStepped(
@@ -130,7 +134,8 @@ function PacejkaWheel.UpdateStepped(
 	local torque = self.baseTorque -- +ve when accelerating, -ve when braking
 	local lateralForce = 0
 	local longitudinalForce = 0
-	local longitudinalSlip = longitudeVelocity - self.angularVelocity * self.radius -- -ve when accelerating, +ve when braking.
+	local wheelContactVelocity = self.angularVelocity * self.radius
+	local longitudinalSlip = longitudeVelocity - wheelContactVelocity -- -ve when accelerating, +ve when braking.
 
 	-- Pacejka mysterious and magical constants.
 	-- See http://www-cdr.stanford.edu/dynamic/bywire/tires.pdf.
@@ -167,11 +172,11 @@ function PacejkaWheel.UpdateStepped(
 
 		if abs(speed) > 2.5 then
 			-- Lateral force component (F_y -> Fy)
-			local FyC = 1.30
-			local FyD = -22.1 * Fz ^ 2 + 1011 * Fz
-			local FyBCD = 1078 * sin(1.82 * atan(0.208 * Fz))
+			local FyC = 1.35 -- 1.30
+			local FyD = 1.00 * Fz * 1000 -- -22.1 * Fz ^ 2 + 1011 * Fz
+			local FyBCD = (13.5 * Fz ^ 1.07) * 1000 -- 1078 * sin(1.82 * atan(0.208 * Fz))
 			local FyB = FyBCD / (FyC * FyD)
-			local FyE = 0 * Fz ^ 2 - 0.354 * Fz + 0.707
+			local FyE = 0.78 - 0.025 * Fz -- 0 * Fz ^ 2 - 0.354 * Fz + 0.707
 
 			-- Lateral force camber angle factor
 			local FySh = 0.028 * camberAngle
@@ -187,13 +192,21 @@ function PacejkaWheel.UpdateStepped(
 			-- 	* REALISTIC_GRAVITY
 			-- 	* (sin(contactLinkOrientationX + PI / 2) * (1 - lateralVelocity * 0.4) - lateralVelocity * 0.1)
 
-			-- NOTE: Lazy solution is using the suspension's global force
-			lateralForce = lateralVelocity * 900
+			local forceAttachmentRightVector = self._forceAttachment.WorldCFrame.RightVector
+			local y = math.atan2(forceAttachmentRightVector.Z, forceAttachmentRightVector.X)
+			local relativeRightVector = CFrame.Angles(0, -y, 0)
+				:VectorToObjectSpace(self._forceAttachment.WorldCFrame.RightVector)
+
+			lateralForce = verticalForce * tan(atan2(relativeRightVector.X, relativeRightVector.Y) - PI / 2)
+				+ lateralVelocity * 900
 		end
 
 		-- Longitudinal force component (F_x -> Fx)
 		if longitudeVelocity ~= 0 then
-			percentLongitudinalSlip = longitudinalSlip / abs(longitudeVelocity) * 100 * min(1, abs(speed) * 0.07)
+			percentLongitudinalSlip = longitudinalSlip
+				/ max(abs(longitudeVelocity), abs(wheelContactVelocity))
+				* 100
+				* min(1, abs(speed) * 0.07)
 
 			local FxC = 1.65
 			local FxD = -21.3 * Fz ^ 2 + 1144 * Fz
@@ -255,6 +268,7 @@ function PacejkaWheel.UpdateStepped(
 			-- 	deg(atan2(contactNormal.Y, contactNormal.Z)),
 			-- 	deg(atan2(contactNormal.Y, contactNormal.X))
 			-- )
+
 			-- print("-")
 		end
 	end
@@ -276,7 +290,7 @@ function PacejkaWheel.UpdateStepped(
 	-- Wheel rotation
 	-- local angularVelocityRelative = longitudeVelocity / self.radius - self.angularVelocity
 
-	self.angularVelocity += torque * deltaTimeSim
+	self.angularVelocity += torque / self._wheelInertia * deltaTimeSim
 
 	self.rotation += self.angularVelocity * deltaTimeSim
 	if (self.rotation :: number) > TWO_PI then

src/landvehicle/src/Client/Classes/Wheels/WheelVehicleWheelClient.luau

@@ -28,11 +28,11 @@ export type Wheel = typeof(setmetatable(
 		_sign: number,
 		_lastUpdated: number,
 		_previousLongitudeVelocity: number,
+		_forceAttachment: Attachment,
 		attachment: Attachment,
 		angularVelocity: number, -- radians per second
 		baseTorque: number,
 		radius: number,
-		force: VectorForce,
 		rotation: number, -- radians
 		mass: number,
 	},
@@ -42,7 +42,8 @@ export type Wheel = typeof(setmetatable(
 function Wheel.new(
 	wheelObj: BasePart,
 	wheelConfig: WheelVehicleTypes.WheelConfig,
-	links: WheelVehicleUtils.Links
+	links: WheelVehicleUtils.Links,
+	forceAttachment: Attachment
 ): Wheel
 	local attachment = wheelObj:FindFirstChild("RigidAttachment")
 	assert(attachment, "Expected wheelObj to have a RigidAttachment")
@@ -51,6 +52,7 @@ function Wheel.new(
 
 	self._config = wheelConfig
 	self._links = links
+	self._forceAttachment = forceAttachment
 	self._previousLongitudeVelocity = 0
 	self.angularVelocity = 0
 	self.baseTorque = 0