Arma Reforger:Vehicle: Wheeled Simulation

Input (Controller)

SCR_CarControllerComponent

General

Param	Type	Unit	Description
Type			Type of gearbox Automatic - Automatic shifting and transition to reversing, W/S - throttle/brake or brake/throttle when reversing. Manual - Manual shifting, W - always throttle, S - always brake, Q/E to shift gears
Transmission RND	bool		Transmission have three settings: reverse, neutral and drive

Steering speed coefficients

The following are properties for smoothing the digital or small range/insensitive analog input (gamepad thumbstick). The setup should be quick and responsive enough while allowing the player to keep a smooth ride (e.g. by tapping the keys), without having to constantly counter compensate.

Param	Type	Unit	Description
Steering Forward Speed	pairs of floats	[vehicle speed in km/h, steering speed in °/s]	Pairs of velocity and steering speed at the given velocity
Steering Backward Speed	pairs of floats	[vehicle speed in km/h, steering speed in °/s]	Pairs of velocity and counter-steering speed (recentering via input) at the given velocity
Steering Center Speed	pairs of floats	[vehicle speed in km/h, centering speed in °/s]	Pairs of velocity and recentering speed (when no steering input is given / caster effect) at the given velocity

Throttle

Param	Type	Unit	Description
Throttle Curve	pairs of floats	[engine rpm, amount of throttle]	Throttle application with respect to engine's RPM
Reverse Curve	pairs of floats	[engine rpm, amount of throttle]	Throttle application with respect to engine's RPM while in reverse
Throttle Reaction Time	float	s	Time (in seconds) it takes to get wanted value of throttle - e.g. to interpolate from 0.0 to 1.0 throttle input
Throttle Turbo Time	float	s	Time (in seconds) to reach wanted value of throttle in turbo mode
Throttle Turbo	float		Amount of throttle that is reserved for turbo mode. For instance 0.2 means that without turbo, vehicle will be moving with maximum 0.8 throttle

Brake

Param	Type	Unit	Description
Braking Curve	pairs of floats	[time in seconds, amount of braking force]	Brake application over time
Brake Turbo Time	float	s	Time to reach wanted value of brake in turbo mode

Engine

Param	Type	Unit	Description
Max Startup Time	float	seconds	Failsafe time for the engine to start (it can also bypass animations if it is shorter)
Max Startup Attempts	float		How many times you can be "stuck" in the startup loop animation
Engine Startup Chance	float	%	Probability that each startup attempt has to turn on the engine (0 - 100) (should be tied to engine below "damaged" threshold)
Air Intakes	float	array of PointInfo classes	Air intake positions in local vehicle space
Drowning Time	float	s	Amount of time needed to completely drown the engine when all air intakes are underwater
Shutdown Time	float	s	Amount of time (some) vehicle systems automatically toggle off after the shutdown
Max Lights Time	float	s	Maximum amount of time the light toggle should take (or if there are no animations)

Clutch

Param	Type	Unit	Description
Clutch Uncouple Time	float	seconds	Time to disengage clutch before switching gears
Clutch Couple Time	float	seconds	Time to engage clutch after switching gears
Clutch Uncouple Rpm	float	RPM	Engine RPM at which clutch is fully uncoupled while moving off
Clutch Couple Rpm	float	RPM	Engine RPM at which clutch is fully coupled while moving off
Clutch Uncouple Factor	float		Clutch uncouple RPM factor while moving off uphill or downhill
Clutch Couple Factor	float		Clutch couple RPM factor while moving off uphill or downhill
Clutch Minimum Position	float		Minimum clutch position while moving off
Clutch Minimum Factor	float		Minimum clutch position factor while moving off uphill or downhill

Shifting

Param	Type	Unit	Description
Slope Smoothing	float		Factor of filter that smooths out upshift and downshift RPMs
Latency	float	seconds	Minimum time between gear switches
Up Shift Factor	float		Upshift RPM factor while going uphill or downhill
Up Shift Rpm	float	RPM	Engine RPM required for upshifting
Down Shift Factor	float		Downshift RPM factor while going uphill or downhill
Down Shift Rpm	float	RPM	Engine RPM required for downshifting
Turbo Shift Factor	float		Upshifting and downshifting RPM ratio in Turbo mode

Simulation

VehicleWheeledSimulation

General

Param	Type	Unit	Description
Solver Type			Solver selector - only V1 solver is available right now
Solver Update Rate		Hz	Solver update rate in Hz (number of ticks per second)

Engine

Controls engine power and its other properties. All values must be greater than 0 to be accepted as valid.

The engine is simulated as rotating cylinder around its central axis (simplification of crankshaft).

Param	Type	Unit	Description	References
Inertia	float	kg.m2	Moment of inertia	https://www.researchgate.net/publication/258176892_Evaluation_of_variable_mass_moment_of_inertia_of_the_piston-crank_mechanism_of_an_internal_combustion_engine
Max Power	float	kW	Maximum power that the engine can provide	You can use this calculator to visualize RPM curve maxTorqueRPM <= maxPowerRPM < maxRPM Use https://www.automobile-catalog.com/ , https://www.dieselhub.com/ and similar sources to check for real torque/power curves of the engines
Max Torque	float	Nm	Maximum torque that engine can provide (peak torque)
Rpm Max Power	float	RPM	RPM where engine outputs maximum power
Rpm MaxT orque	float	RPM	RPM where maximum torque is produced
Rpm Idle	float	RPM	RPM when engine is idling, e.g. in neutral
Rpm Redline	float	RPM	Redline RPM This parameter is currently ignored
Rpm Max	float	RPM	Maximum RPM
Steepness	float		Controls how fast engine can reach max torque. It can be used to flatten the torque curve before max torque rpm are reached
Friction	float		Engine's braking torque
Output			Powertrain part driven by the engine (clutch)

Clutch

Param	Type	Unit	Description
Max Clutch Torque	float	Nm	Maximum torque that clutch can provide. (1.6*MaxTorque can be a good starting point) This parameter is currently ignored
Output			Powertrain part driven by the clutch (gearbox)

Gearbox

Param	Type	Unit	Description
Reverse	float		Reverse gear ratio
Forward	array of floats		Array of forward gear ratios, order of the values are mapped to gears respectively
Efficiency	float		Transmission efficiency - scales the engine output passed down
Output			Powertrain part driven by the gearbox (differential)

Differentials

Param	Type	Unit	Description
Type	Open		Same torque on both outputs, different rotational speeds
	LSD		Limited slip differential - limiting rotational difference between outputs. Opens Anti slip and Anti slip torque parameters.
Ratio	float		Differential ratio (sometime "final drive")
Strength	float		Determines the magnitude of the extra force that is applied to the gripping wheel
Output0			Powertrain parts driven by the differential (other differential or axle differential)
Output1

Axles

Param	Type	Unit	Description
Torque Share	float		Defines how much torque is delivered to this axle. Sum of Torque Share for all axles should be equal to 1
Has Handbrake	bool		Determines whether this axle is used for handbrakes. Handbrake force is same as Brake Torque

(Axle) Differential

Param	Type	Unit	Description
<same as differentials>
Output0			Driven wheels
Output1

Suspension

Accelerating/braking/turning should noticeably shift the weight of the vehicle. Weight shifting affects the grip of the tires - allowing more grip on the side with more weight. Center of mass should be set realistically high and the tendency to roll should be limited by a sway (anti-roll) bar if necesary, not by setting the CoM below the vehicle or just the wheel center.

Param	Type	Unit	Description
Max Steering Angle	float	degrees	Specifies the maximum steering angle of this axle, if negative value is given, the axis will steer in opposite direction of the steering wheel.
Spring Rate	float	N/mm	Spring force per mm.
Compression Damper	float	Ns/m	Compression damper force per 1m/s.
Relaxation Damper	float	Ns/m	Relaxation damper force per 1m/s.
Max Travel Up	float	m	Maximum distance that the suspension can be compressed from modeled position. Standard cars 0.06 - 0.1 m. Off-road cars >0.1 m.
Max Travel Down	float	m	Maximum distance that the suspension can be expanded from modeled position. Standard cars 0.07 - 0.12 m. Off-road cars >0.1 m.

Wheel

Param	Type	Unit	Description
Radius	float	m	Radius of the wheel
Ratio	float		Wheel reduction ratio
Mass	float	kg	Mass of the wheel on this axle
Brake Torque	float	Nm	Amount of brake torque applied to each wheel on this axle

Tyre

Param	Type	Unit	Description
Rolling Resistance	float		Currently not used in game Linearly proportional to speed. Acts against the wheel torque. For limiting acceleration. (in addition to surface property)
Rolling Drag	float		Currently not used in game Proportional to speed squared. For limiting high speeds. (in addition to surface property)
Roughness	float	m	Bumpiness height - how bumpy is the wheel itself (in addition to surface property)
Longitudinal Friction	float		Directly affects tyre grip in longitudinal direction
Lateral Friction	float		Directly affects tyre grip in lateral direction
Tread	float		Ratio of the "Thread" - related to how well wheel performs on specific surface.

Swaybar

Param	Type	Unit	Description
Stiffness	float	N	Sway bar stiffness ( anti-roll force )

Inertia

• InertiaOverrideEnable
  • Enables manual override of vehicle inertia - the way how to "simulate" mass distribution on the vehicle.
• InertiaOverride
  • Inertia values around each axis. Copy initial values from diag or via context menu opened on VehicleWheeledSimulation on the Entity instance (you have to Apply to prefab later)

Aerodynamics

Param	Type	Unit	Description
Reference Area	float	m2	Drag reference area - see following page for more details https://en.wikipedia.org/wiki/Automobile_drag_coefficient#Drag_area
Drag coefficient	float		Drag coefficient - see following page for more details https://en.wikipedia.org/wiki/Automobile_drag_coefficient#Typical_drag_coefficients

Pacejka

• https://www.edy.es/dev/docs/pacejka-94-parameters-explained-a-comprehensive-guide/
• http://www.racer.nl/pacejka/pacplay.htm

Fill in initial values via context menu opened on VehicleWheeledSimulation on the Entity instance (you have to Apply to prefab later)

Longitudinal

b0

Param	Role	Units	Typical range	Sample	Description	Dependency
Shape factor		1.4 .. 1.8	1.5	General shape of the curve. Defines the amount of falloff after the peak. The Pacejka model defines b0 = 1.65 for the longitudinal force.	Load-independent
b1	Load influence on longitudinal friction coefficient (*1000)	1/kN	-80 .. +80	0	Change of the friction coefficient at the peak. Positive = more friction with more load. Negative = less friction with more load.	Load-dependent
b2	Longitudinal friction coefficient (*1000)		900 .. 1700	1100	Friction coefficient at the peak (vertical coordinate) *1000.	Load-independent
b3	Curvature factor of stiffness/load	N/%/kN^2	-20 .. +20	0	Change of the peak’s horizontal position. Positive = increases ascent rate with load (moves to the left). Negative = decreases ascent rate with load (moves to the right).	Load-dependent
b4	Change of stiffness with slip	N/%	100 .. 500	300	Peak’s horizontal position specified as “ascent rate”.	Load-independent
b5	Change of progressivity of stiffness/load	1/kN	-1 .. +1	0	Lineal change of the peak’s horizontal position. Similar to b3 but more lineal and with reverse effect positive-negative. Positive = decreases ascent rate with load. Negative = increases ascent rate with load.	Load-dependent
b6	Curvature change with load^2		-0.1 .. +0.1	0	Quadratic change of the curvature at the peak. Positive = more flat with load. Negative = sharper with load.	Load-dependent
b7	Curvature change with load		-1 .. +1	0	Change of the curvature at the peak. Same as b6 but more lineal. Positive = more flat with load. Negative = sharper with load.	Load-dependent
b8	Curvature factor		-20 .. +1	-2	Curvature at the peak. The more negative = more “sharp”. Has influence on the falloff afterwards.	Load-independent
b9	Load influence on horizontal shift	%/kN	-1 .. +1	0	Change of the horizontal shift. Positive = shifts to the left with more load. Negative = shifts to the right with more load.	Load-dependent
b10	Horizontal shift	%	-5 .. +5	0	Curve’s horizontal shift	Load-independent

Lateral

a0

Param	Role	Units	Typical range	Sample	Description	Dependency
Shape factor		1.2 .. 18	1.4	General shape of the curve. Defines the amount of falloff after the peak. The Pacejka model defines a0 = 1.3 for the lateral force.
a1	Load influence on lateral friction coefficient (*1000)	1/kN	-80 .. +80	0	Change of the friction coefficient at the peak. Positive = more friction with more load. Negative = less friction with more load.	Load-dependent
a2	Lateral friction coefficient (*1000)		900 .. 1700	1100	Friction coefficient at the peak (vertical coordinate) *1000.
a3*	Change of stiffness with slip	N/deg	500 .. 2000	1100	Peak’s horizontal position at the reference load, specified as “ascent rate”.
a4*	Change of progressivity of stiffness / load	1/kN	0 .. 50	10	Change of the peak’s horizontal position with load. Smaller value = bigger change with load.
a5	Camber influence on stiffness	%/deg/100	-0.1 .. +0.1	0	Change of the peak’s horizontal position. Positive = decreases ascent rate with camber (moves to the right). Negative = increases ascent rate with load (moves to the left).	Camber-dependent
a6	Curvature change with load		-2 .. +2	0	Change of the curvature at the peak. Positive = more flat with load. Negative = sharper with load.	Load-dependent
a7	Curvature factor		-20 .. +1	-2	Curvature at the peak. The more negative = more “sharp”. Has influence on the falloff afterwards
a8	Load influence on horizontal shift	deg/kN	-1 .. +1	0	Change of the horizontal shift. Positive = shifts to the left with more load. Negative = shifts to the right with more load.	Load-dependent
a9	Horizontal shift at load = 0 and camber = 0	deg	-1 .. +1	0	Curve’s horizontal shift
a10	Camber influence on horizontal shift	deg/deg	-0.1 .. +0.1	0	Change of the horizontal shift. Same sign as camber = shifts to the left. Opposite sign as camber = shifts to the right.	Camber-dependent
a11	Vertical shift	N	-200 .. +200	0	Curve’s vertical shift
a12	Vertical shift at load = 0	N	-10 .. +10	0	Vertical shift when approaching zero load. Must be verified for coherency at the configured minimum load.	Load-dependent
a13	Camber influence on vertical shift, load dependent	N/deg/kN	-10 .. +10	0	Change of the vertical shift according to camber and load. Same sign as camber = shifts upwards. Opposite sign as camber = shifts downwards. The more load the more camber effect.	Camber-dependent
a14	Camber influence on vertical shift	N/deg	-15 .. +15	0	Change of the vertical shift. Same sign as camber = shifts upwards. Opposite sign as camber = shifts downwards.	Camber-dependent

^{* Configure the horizontal behavior with load}

Aligning

Param	Role	Units	Typical range	Sample	Description	Dependency
c0
c1
c2
c3
c4
c5
c6
c7
c8
c9
c10
c11
c12
c13
c14
c15
c16
c17
c18

RaycastLayer

• LayerPreset in which the wheel raycast is performed (should be "Vehicle")

RigidBody and Center of Mass

• All vehicles are set to curb weight (assuming dynamic weight could happen at some point in the future)
• Center of Mass plays a crucial role in vehicle handling - it should be high enough to allow for weight shifting and changes in the wheel grip due to the changing pressure.