Vehiclewheel, Vehiclebody and the unpredictabilty of life

green-baron

Hi, i've been playing around with these for 2 weeks now and i don't get it. I'm frustrated  <img src="https://godotdevelopers.org/forum/resources/emoji/frowning.png" alt="" height="20">. Example (and i must admit that i'm new to game development): i've been messing around for two weeks now with vehiclebodies, vehiclewheels and rigidbodies in combination. My problem is that i cannot reproduce the behaviour between one test and another, it seems to be arbitrary and unpredictable. Things hop around or sink through the ground, mass switches seem to have no effect or a big one. Small changes make huge differences in one place, have no effect in others. Is there any possibilty to get behind the meaning of masses and friction of bodies (be they rigid, vehicle or whatever), the effect of rest length (and the difference to travel of suspension) and friction slip of wheels, stiffness and maxforce of suspension ? And what do damping/relaxation really do ? Example: i have a chassis with 4 wheels, it runs on a flat ground (but trembles slightly, i can't control that, the trucks of the truck town example don't tremble). When i add a rigidbody (vehicle as child of rigid) it falls through the ground (which is a flat static body). Another example: changing the damping of a wheel makes the vehiclebody detach (sinks through the ground), the wheels sink half way in. I don't get it. I wrote a script to play with the numbers and see the effects, but the behaviour is just strange and frustrating. Ok, to make it short: has anyone yet been successful with complex vehicles (involving rigidbodies, animations and changing masses, the latter being crucial) and made a tutorial or has written down his/her experiences somewhere ? I searched youtube and the forum but haven't found anything helpful yet. Before i haven't solved that problem it'll be difficult to continue ... Thanks for any advice and input !

NeoD

Hello ! The shakeness is probably due to the center of mass setting. So, check if the body vehicle position is equal to the center of the collision shape. There's an issue who limits greatly the ability to set the center of mass but vehicles aren't the current priority of the next Godot releases.For the other question I wonder why you want to place the vehicle as a child of a rigidbody ?

green-baron

Hi,and thanks for the input so far.I checked the translation-vector of the collision shapes, they are all 0,0,0 with respect to their parents (chassis (vehicle) and body (rigid)).I also switched the rigidbody to be a child of the vehiclebody. My thinking was that for example the body of a plane (or car, or train wagon) has a different collider than the rest (chassis, wheels). I can think of a different approach, involving a single rigidbody.But now a funny thing happens: the whole contraption settles, then flies apart in two parts, rigidbody in one direction, vehicle in another, spinning rapidly ...[url=http://picload.org/image/rgrlipor/car_test.png]http://picload.org/image/rgrlipor/car_test.png[/url]Where you trying to say that i should use a single collider on the vehicle and calculate the collsions with the help of rays for instance ? Always open for a change of thoughts :-)

NeoD

Assuming you want to separate your vehicle in two bodies, IMHO, you don't need to make your rigid body a child or a parent of your body vehicle.In the Trucktown demo the trailer and the vehicle who pull the trailer (I don't know the exact English word) are two brothers, both are childs of a spatial node.

green-baron

Thanks NeoD,nope, from a construction point of view it's a single body. It's sort of a plane, meaning it needs ground vehicle functionality when taxiing (hence the vehiclebody) but still relies on the correct masses when in the air (for applying thrust, lift, resistance, gravity, centrifugal and -petal force). Of course i'd like to use the built in physics engine to apply the corresponding forces/impulses to the (rigid-?)body.It seems to me that using large masses in the bodies make it difficult to control the ... "structural integrity :-)". Low masses in the 10s (like in the truck town cars) are no problem, large ones in the 10.000s (assuming kg here just for convenience) shake and tremble and then sink through ground or fly apart or just move along slowly, shivering. Problem is, a plane has 10.000s of kg.I'll try the following: internally i'll use the right numbers for calculation, but for physics i'll normalize the numbers to ... something lower when on the ground.