Axles in vehicle?

[pHySiQuE]

What exactly does the AddAxle() command do? Why do vehicles need an axle specified? Does this make the right and left tire move in unison? Wouldn't the steering wheels rotate independently and not use an axle?

[Julio Jerez]

axle define how the differential ratio is distribute to each tire. They are precisely so that the tires do not move in unison when they do not need to, when a vehicle is turning the torque delivered to the tires must change by certain amount. this value is given by an identity that relate the input torque, the instant power and the angular velocity of each tire. http://web.mit.edu/2.972/www/reports/differential/differential.html
The Axle class implements this identity

They are an important part of the vehicle implementation.
a rear wheel drive car will have one differential that plug the rear wheel to the engine,
and four wheel drive needs three differential, on ether connect the engine tow the front and rear differential and the rear and front differential, and multiply tire vehicle need a mutidifrental.
and a Track vehicle needs a skid differential.

not using differential to distribute the engine torque to the tire, is the equivalent to calculate ration force with out contact joints.

are you having problem with that?

[AntonSynytsia]

Including, when it comes to steering, the inner front wheel steers at the greater angle than the outer front wheel to avoid scrub. I don't know if this is implemented into the vehicle class though.

steering concept.png (33.75 KiB) Viewed 3160 times

[Sweenie]

Including, when it comes to steering, the inner front wheel steers at the greater angle than the outer front wheel to avoid scrub. I don't know if this is implemented into the vehicle class though.

Ackermann steering
http://en.m.wikipedia.org/wiki/Ackerman ... g_geometry

Tried it some years ago in my vehicle implementation and it made the vehicle maintain more of it's velocity while turning, mostly noticeable at lower velocities.

[Julio Jerez]

Tried it some years ago in my vehicle implementation and it made the vehicle maintain more of it's velocity while turning, mostly noticeable at lower velocities.

yes that is precisely what is does, and is is full supported in the engine.

Code: Select all

void CalculateAkermanParameters (
const CustomVehicleControllerBodyStateTire* const rearLeftTire, const CustomVehicleControllerBodyStateTire* const rearRightTire,
const CustomVehicleControllerBodyStateTire* const frontLeftTire,
const CustomVehicleControllerBodyStateTire* const frontRightTire);

after the frond a rear wheel are set you call that function of the steering compopnets

Code: Select all

      CustomVehicleControllerComponentSteering* const steering = new CustomVehicleControllerComponentSteering (m_controller, VIPER_TIRE_STEER_ANGLE * 3.141592f / 180.0f);
      steering->AddSteeringTire(leftFrontTire);
      steering->AddSteeringTire(rightFrontTire);
      steering->CalculateAkermanParameters (leftRearTire, rightRearTire, leftFrontTire, rightFrontTire);

it is the steering that makes a the differential distribute torque different to each tire, but that's not the only reason.
The vehicle is not a naïve implementation, it is in fact quite sophisticated for a Real time engine, and the best of all is that It is possible to ass more realism because it is a full articulate body.
This is no the typical ray cast car you see in commercial physics library.

[AntonSynytsia]

That's awesome!

[manny]

That is really awesome. Topic answered, topic locked