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motor vehicles come in a huge variety of
shapes and designs each tailored for a
specific purpose whether that be simply
getting you from A to B in comfort and
safety traveling around a well paved
racetrack in the shortest time possible
crossing difficult terrain or just
sliding around the corner in style each
have been carefully crafted by their
engineers to excel in their disciplines
last month ubisoft invited me to the red
bull ring in austria to drive four
incredibly different vehicles the KTM
crossbow an ultra lightweight tracker
driven by a professional driver an
off-road buggy a Land Rover Defender and
a Porsche Cayman S driven by a complete
idiot all this to get a better idea of
how these vastly different vehicles
perform in real life and to discuss with
the programmers of Ubisoft's new game
the crew - about their process for
programming their vehicles how to behave
in game Oh my name is Stefan Jankowski
and I'm producer at ivory tower UV
substitute I'm the crew - obviously
speaking with the fan I started to get a
much better idea of the relationship
between real-world physics and in-game
physics and just how developers program
vastly different vehicles like these to
perform like their real-life
counterparts
unlike real-life where a boy racers love
to destroy their cars with modifications
that negatively affect performance the
in-game engine separates the physics
model from the 3d model when we do the
3d model that's one part of the vehicle
and then we have the pure physic model
that is completely separate from the 3d
the physics model creates a model where
things like the wheels are independent
physics objects with their own friction
and mass modelled the separate 3d model
allows the developer to pick and choose
what cosmetic changes to the vehicle
affect performance
for example spoilers are not treated as
aerodynamic surfaces in the crew - so
your inner idiot can apply spoilers and
front-wheel drive cars to your heart's
content one of the few cosmetic features
in-game that does affect performance of
the vehicle is the suspension
suspensions are a system of springs
shock absorbers and linkages that
connect the vehicle body to its wheels
with the goal of keeping the tires in
contact with the ground while minimizing
the transfer of that motion to the
vehicle body the
provides comfort for the passengers of
the vehicle not much of a concern for a
videogame but they also determine how
the vehicle will handle bumps and
corners off-road vehicles have
incredibly soft suspension this allows
them to run over rugged terrain at high
speed without transferring too much
force to the body of the vehicle
but with one significant drawback while
cornering or driving over slanted ground
a large amount of the weight of the
vehicle is shifted onto one side of the
car with suspension this soft the
vehicle is extremely susceptible to roll
as the body is fairly free to tilt upon
the wheels combine that with a fairly
high center of mass and it's a disaster
waiting to happen especially when you
put an attention-seeking australian
vlogger in the driving seat and while
you can't roll over your vehicle in-game
as the physics engine applies a torque
to the car when it rolls too far but it
does allow enough roll for the
suspension model to behave realistically
which feeds into the traction physics
model car is designed for tracks will
always have stiff suspensions this helps
them keep their tires in contact with
the ground
ensuring traction is not lost in corners
through tilting while maintaining a
consistent ride height an important
characteristic for vehicles like the
crossbow as its undercarriage forms a
significant part of its downforce
generation through its rear diffuser
it's important to maintain a low center
of gravity too as this minimizes that
rolling effect we saw earlier the one
drawback of stiff suspension like this
is right Comfort I was in the passenger
seat of the crossbow for a couple of
laughs and boy do you feel every bump
you can see the effect of suspension
stiffness and weight distribution which
is simulated in the physics model
accurately on traction very well in game
with front-engined rear-wheel drive cars
like the Ford Mustang GT that is
particularly easy to drift around the
corner by lifting off the accelerator
and hitting the brake at the apex of a
turn the g-forces of deceleration causes
the heavy front end of the vehicle to be
pushed downwards lifting the rear axle
and causing the rear tires to lose grip
thus initiating over steering this is a
lot of fun and the penalties on speed in
game are fairly miniscule but in real
life this is something designers of
racing vehicles want to avoid as you
cannot apply full power if your wheels
are slipping and you lose forward
velocity by sliding sideways so most
racing vehicles are
mid-engine to maintain grip on the rear
tires during braking and keep the
suspensions if to ensure the balance
between tires is as close to the ideal
as possible keeping the weight evenly
distributed between the front and rear
tires in corners is important because it
creates a vehicle which does not over or
understeer over searing beam drifting
where the back wheels construction and
under steering is where the front tires
lose traction diminishing the steering
wheels ability to dictate the direction
of the car allowing momentum to take
over in a race you want neither but this
is a video game so you can adjust both
your front axle grip and rear axle grip
to encourage these effects this slider
simply adjusts the coefficient of
friction being applied to the tires in
the in-game physics engine which adjusts
the traction force the tires can apply
to the ground traction is one of the
primary tools the developers will play
around with to change the feel of the
game as this is the variable that
dictates how the vehicle will interact
with the road more realistic games like
simulators will do their best to model
traction as realistically as possible
but may give you optional driving
assistance to make the game easier for
example at higher speeds the max
steering angle will be limited to help
with overtaking with clumsy Tom stick
controls leading tamanna car is behaving
like under steering cares where if you
take corners at too high speed you will
end up crashing into the barrier but
without the driving assist the result
would be pretty similar anyways you may
have just spun a few times instead like
I did when driving the Porsche with the
traction control off you just need to
learn to manage your speed in corners
better games aiming for an arcade feel
may do away with this mechanic and
separate traction from steering
mechanics altogether allowing you to
take corners at any speed with no worry
the crew to land somewhere in the middle
it's obviously an arcade game you can
take ridiculous jumps like this in a
Ford f-150 Raptor race truck at 180 km/h
and land without destroying your car and
then take a turn at 200 kilometers an
hour on a dirt track without losing
lateral traction the traction here has
just been boosted to make the game
easier and more fun to play next up
let's look at how the power of the
engines are handled
now obviously the computer programmers
do not simulate an entire engine and
transmission system to determine the
vehicle performance take this Porsche
911 gt3 RS in this clip it does 0 to 100
kilometers an hour in 3.2 seconds
pretty much identical to its real-life
counterpart even with the nitrous boost
the programmers want the relative
performance between vehicles to be
relatively accurate as it would make no
sense of a Mazda rx-7 was beating a
Porsche 911 GTS an acceleration and top
speed to understand how acceleration and
top speed are programmed we first need
to examine what forces are acting to
slow the vehicle down the top speed of a
car is primarily dictated by the drag
force acting on the vehicle which is
something we examined before in my
helicopter versus carrot top speed video
the equation for drag force is provided
by this equation and the equation for
power is simply force times velocity by
rearranging these variables we get this
equation for top speed which the physics
engine uses to limit the vehicles top
speed the programmers can adjust the top
speed of each vehicle simply by
adjusting its max power coefficient of
drag or frontal area if they really want
to do they could change the air density
with elevation on the map to adjusting
the acceleration is slightly more
difficult as the acceleration is
determined by several factors which vary
with the vehicle speed the primary
variable that we are concerned with is
the wheel torque which varies
dramatically for internal combustion
engines across different engine rotation
speeds and gear ratios the force applied
by the wheel to the ground
if there is no tire slip will vary with
the torque applied divided by the wheel
radius the wheel radius is just one part
of the internal gearing system that
needs to be considered when calculating
the force the wheels will impart on the
ground the vehicle will have several
gears that can cycle through at
different speeds to change the applied
wheel torque and will have one permanent
drive ratio that is determined by
additional gearing and things like the
differential all these parameters will
be programmed into the in-game vehicle
and the final wheel torque will be
determined by this equation
where te is the engine torque the engine
torque varies across different
revolutions per minute of the engine and
we defined that variation with a torque
curve like this one for the Porsche
Cayman S the programmers will again
actually input the vehicle's torque
curve into the vehicle parameters to
ensure it performs like the real deal
designing games like this is always a
delicate balance between realism and fun
the developers don't always go for ultra
realism programmers will often play
around with their
world's physics variables like lateral
traction to give her more arcadey feel
with exaggerated drifting or simply to
make the car easier to drive around
corners at high speed or we can just
throw the rulebook out the window and
switch from being a plane to a boat in
midair
there is no real odd read here I simply
want to say thank you to Ubisoft for
inviting me out to such a cool event and
allowing me to chat with the programmers
of the game if you're into car video
games the crew tube is out now
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