Car parameters for vdrift-2009-06-15 and older
The file's fields are mostly the same as the Vamos car parameters, explained in the Vamos docs. The units are all in MKS (meters, kilograms, seconds). It might also help to read The Physics of Racing by Brian Beckman.
The file contains several sections. Each section will now be described, along with example values from the XS.car file. The XS has performance comparable to the Honda S2000.
Top level parameters
drive = RWD
The only top level parameter is the "drive" parameter. It accepts values "RWD", "FWD", "AWD" that correspond to rear wheel drive, front wheel drive, and all wheel drive, respectively.
Steering
max-angle = 33.19
This defines the maximum angle that the wheels will turn in each direction. For the XS, when the steering wheel is full left, the wheels would be at -33.19 degrees.
Engine
position = 0.86, 0.0, -0.21 mass = 140.0 max-power = 1.79e5 peak-engine-rpm = 7800.0 rpm-limit = 9000.0 inertia = 0.25 idle = 0.02 start-rpm = 1000 stall-rpm = 350 fuel-consumption = 1e-9 torque-friction = 0.0003 torque-curve-00 = 1000, 140.0 torque-curve-01 = 2000, 149.14 torque-curve-02 = 2200, 145.07 torque-curve-03 = 2500, 147.78 torque-curve-04 = 3000, 169.50 torque-curve-05 = 3300, 172.19 torque-curve-06 = 4000, 169.50 torque-curve-07 = 4500, 166.77 torque-curve-08 = 5600, 172.19 torque-curve-09 = 5800, 170.83 torque-curve-10 = 6000, 168.12 torque-curve-11 = 6100, 177.61 torque-curve-12 = 6200, 186.42 torque-curve-13 = 6300, 192.53 torque-curve-14 = 6500, 195.92 torque-curve-15 = 6700, 195.92 torque-curve-16 = 7000, 195.24 torque-curve-17 = 7600, 190.49 torque-curve-18 = 8000, 184.39 torque-curve-19 = 8200, 183.04 torque-curve-20 = 8300, 146.43 torque-curve-21 = 9500, 146.43
The position and mass parameters affect the weight distribution of the car. The torque curve is calculated from max-power and peak-engine-rpm using a polynomial expression given in Motor Vehicle Dynamics, Genta (1997), where peak-engine-rpm is the engine speed at which the maximum power output (max-power) is achieved. Alternatively, the torque curve can be explicitly defined, as in the example above. A rev limit can be set with rpm-limit. The rotational inertia of the moving parts is inertia. idle is the throttle position at idle. Starting the engine initially sets the engine speed to start-rpm. Letting the engine speed drop below stall-rpm makes the engine stall. The rate of fuel consumption is set with fuel-consumption.
Clutch
sliding = 0.27 radius = 0.15 area = 0.75 max-pressure = 11079.26
The torque on the clutch is found by dividing the clutch pressure by the value in the area tag and multiplying by the radius and sliding (friction) parameters.
Transmission
gears = 6 gear-ratio-r = -2.8 gear-ratio-1 = 3.133 gear-ratio-2 = 2.045 gear-ratio-3 = 1.481 gear-ratio-4 = 1.161 gear-ratio-5 = 0.943 gear-ratio-6 = 0.763 shift-delay = 0.08
The number of forward gears is set with the gears parameter. The gear ration for reverse and all of the forward gears is then defined. The shift-delay tag tells how long it takes to change gears. For a paddle-shifter, like a modern Formula One car, shift-delay can be set to zero.
Differential
final-drive = 4.100 anti-slip = 600.0
The final drive provides an additional gear reduction. The anti-slip parameter limits the difference in speed between two wheels on the same axle.
Fuel tank
position = -0.8, -0.1, -0.26 capacity = 0.0492 volume = 0.0492 fuel-density = 730.0
The fuel tank's position, the current volume of fuel and the density of the fuel affect the car's weight distribution. The capacity tag sets the maximum volume of fuel that the tank can hold. The initial volume is set with the volume tag. The density of the fuel is set with fuel-density.
Suspension
Front/rear parameters are broken into two fields. Per-wheel parameters are broken into four fields. In the example below the front suspension is shown, followed by the front left wheel.
spring-constant = 49131.9 bounce = 2588 rebound = 2612 travel = 0.19 max-compression-velocity = 10.0 camber = -1.33 caster = 6.12 toe = 0.0 anti-roll = 8000.0
position = 1.14, 0.76, -0.03 hinge = 0,0,0
The hinge is the center of the wheel's path as the suspension moves. The location of the hinge is determined by suspension geometry, and may be outside of the car itself. bounce and rebound are the damping coefficients for compression and expansion of the suspension, respectively. If the speed at which the suspension is compressed, or expanded exceeds the value in max-compression-velocity, the dampers “lock up.” Wheel alignment is set with the camber, caster, and toe tags. All angles are in degrees.
Tire
Front/rear parameters are broken into two fields. In the example below the front tire section is shown.
radius = 0.29 rolling-resistance = 1.3e-2, 6.5e-6 rotational-inertia = 10.0 tread = 0.0 # Lateral force a0=1.6 a1=-38 a2=1201 a3=1914 a4=8.7 a5=0.014 a6=-0.24 a7=1.0 a8=-0.03 a9=-0.0013 a10=-0.15 a111=-8.5 a112=-0.29 a12=17.8 a13=-2.4 # Longitudinal force b0=1.7 b1=-80 b2=1571 b3=23.3 b4=300 b5=0 b6=0.0068 b7=0.055 b8=-0.024 b9=0.014 b10=0.26 b11=-86 b12=350 # Aligning moment c0=2.3 c1=-3.8 c2=-3.14 c3=-1.16 c4=-7.2 c5=0.0 c6=0.0 c7=0.044 c8=-0.58 c9=0.18 c10=0.043 c11=0.048 c12=-0.0035 c13=-0.18 c14=0.14 c15=-1.029 c16=0.27 c17=-1.1
The two elements of rolling-resistance are the constant and velocity-squared terms, respectively. Radius defines the radius of the tire. The tread parameter ranges over arbitrary values of 0.0 to 1.0, where 0.0 is a road tire and 1.0 is an off-road tire. The longitudinal, transverse, and aligning section each contain a vector of “magic formula” coefficients as presented in Motor Vehicle Dynamics, Genta (1997). A description is shown below:
Shape factor ........................................... A0 Load infl. on lat. friction coeff (*1000)... (1/kN) .... A1 Lateral friction coefficient at load = 0 (*1000) ....... A2 Maximum stiffness ........................ (N/deg) ..... A3 Load at maximum stiffness ................ (kN) ........ A4 Camber infiuence on stiffness ............ (%/deg/100) . A5 Curvature change with load ............................. A6 Curvature at load = 0 .................................. A7 Horizontal shift because of camber ........(deg/deg).... A8 Load influence on horizontal shift ........(deg/kN)..... A9 Horizontal shift at load = 0 ..............(deg)........ A10 Camber influence on vertical shift ........(N/deg/kN)... A111 Camber influence on vertical shift ........(N/deg/kN**2) A112 Load influence on vertical shift ..........(N/kN)....... A12 Vertical shift at load = 0 ................(N).......... A13 Shape factor ........................................... B0 Load infl. on long. friction coeff (*1000)... (1/kN) ... B1 Longitudinal friction coefficient at load = 0 (*1000)... B2 Curvature factor of stiffness ............ (N/%/kN**2) . B3 Change of stiffness with load at load = 0 (N/%/kN) ..... B4 Change of progressivity of stiffness/load (1/kN) ....... B5 Curvature change with load ............................. B6 Curvature change with load ............................. B7 Curvature at load = 0 .................................. B8 Load influence on horizontal shift ....... (%/kN) ...... B9 Horizontal shift at load = 0 ............. (%) ......... B10 Load influence on vertical shift ......... (N/kN) ...... B11 Vertical shift at load = 0 ............... (N) ......... B12 Shape factor ........................................... C0 Load influence of peak value ............ (Nm/kN**2) ... C1 Load influence of peak value ............ (Nm/kN) ...... C2 Curvature factor of stiffness ........... (Nm/deg/kN**2) C3 Change of stiffness with load at load = 0 (Nm/deg/kN) .. C4 Change of progressivity of stiffness/load (1/kN) ....... C5 Camber influence on stiffness ........... (%/deg/100) .. C6 Curvature change with load ............................. C7 Curvature change with load ............................. C8 Curvature at load = 0 .................................. C9 Camber influence of stiffness .......................... C10 Camber influence on horizontal shift......(deg/deg)..... C11 Load influence on horizontal shift........(deg/kN)...... C12 Horizontal shift at load = 0..............(deg)......... C13 Camber influence on vertical shift........(Nm/deg/kN**2) C14 Camber influence on vertical shift........(Nm/deg/kN)... C15 Load influence on vertical shift..........(Nm/kN)....... C16 Vertical shift at load = 0................(Nm).......... C17
Brakes
Front/rear parameters are broken into two fields. In the example below the front section is shown.
friction = 0.73 max-pressure = 4.0e6 bias = 0.60 radius = 0.14 area = 0.015
The bias parameter is the fraction of braking pressure applied to the front brakes (in the front brake section) or the rear brakes (in the rear brake section). To make sense, the rear value should equal 1.0 minus the front value. The maximum brake torque is calculated as friction * area * bias * max-pressure * radius. Some fraction of this value is applied based on the brake pedal.
Driver
position = -0.62, -0.35, -0.12 mass = 90.0 view-position = -0.64, 0.35, 0.30 hood-mounted-view-position = 0.55, 0, 0.17
The position and mass affect the weight distribution of the car. The view positions define 3D coordinates for camera placement.
Drag
position = 0.0, 0.0, 0.2 frontal-area = 2 drag-coefficient = 0.3
The frontal area and coefficient of drag, set with frontal-area and drag-coefficient, are used to calculate the drag force.
Wing
Front/rear parameters are broken into two fields. In the example below the front section is shown.
position = 1.9, 0.0, 0.60 frontal-area = 0.2 drag-coefficient = 0.0 surface-area = 0.3 lift-coefficient = -0.5 efficiency = 0.95
Downforce can be added with wings. The amount of downforce is determined by the value in the lift-coefficient tag. If the lift coefficient is positive, upforce is generated. This is usually undesirable for cars. The efficiency determines how much drag is added as downforce increases. The surface-area is the surface area of the wing. This value is also used in the drag calculation.
Wheel
Per-wheel parameters are broken into four fields. In the example below the front left wheel is shown.
position = 1.14, 0.76, -0.47 roll-height = 0.29 mass = 18.14 restitution = 0.1
Contact-points
mass = 0.05 position-00 = 1.96, 0.37, -0.24 position-01 = 1.96, -0.37, -0.24 position-02 = 1.52, 0.83, 0.16 position-03 = 1.52, -0.83, 0.16 position-04 = -0.10, 0.89, -0.24 position-05 = -0.10, -0.89, -0.24 position-06 = -2.18, -0.83, -0.10 position-07 = -2.18, 0.83, -0.10
These values are used for weight distribution and balance only. They no longer perform any contact-related function.
Particle
These parameters are broken into a series of values starting at 00 and going to some number less than 100. The particle-00 is shown below.
mass = 30.0 position = -1.28, 0.0, -0.36
These values are used for weight distribution and balance.
