Car weight balance with wheel colliders

Unity Engine
1

I am building a firetruck and have a collider that goes around the entire car including the long rear end behind the wheels. I noticed that if I have that box collider the balance of the car is thrown off and the car leans back more because of the additional weight in the back.

I originally had a box right in the middle of the model so the balance was perfect, but now that I have to add colliders to the car the balance seems off. Is there a way to tell it to not use those box colliders to determine the center of the car?

2

rigidbody.centerofmass

3

I’ll have to try that… I didn’t even think about that. I am assuming the Center of Mass is automatically calculate somehow when the car is initialized because it changes based on the colliders I have under the main rigidbody.

4

every time you add a collider it recalculates COM, so set it after you’ve setup colliders

5

Yeah I still notice a weight there even though I changed the center of mass.

I have to play around with this some more because even though I set the center of mass, colliders still affect the car. Maybe its affects the mass based on how many colliders there are because it doesn’t feel like its the COM anymore, but the car feels heavier when it hits a speed bump it doesn’t hit it as jumpy with more colliders in it.

6

Well, that doesnt sound too un-realistic.

You could always adjust the strength of the rear wheel suspension.

7

Yeah I’m trying not to do that, I want to make the spring values realistic as possible. I guess I can always check the colliders and positions then strengten the springs depending on the colliders on the model, but I don’t think I should have to do that. This should just work…

I ran a test right now and I set the rigid body COM to 0,0,-0.01, then what I did was added 3 cubes with box colliders to the front of the car and it dropped the front end from the weight of the blocks, I checked the COM and it was still set to 0,0,-0.01 and I even set it again to make sure it wasn’t a bug or anything.

Whats funny is I duplicated the box collider that is sitting in front of my car 40 times and it did nothing, I guess because it had already accounted for that collider??? not sure why my existing collider would not affect the model when I duplicated it 40 times, but when I added 2 new box colliders it dropped the model to the ground from the weight.

8

Well, most trucks have extra wheels/suspension in the rear, so I would think it was more realistic for the back to be heavier, especially on a firetruck. Doubt that makes you feel better though! heh

I would expect colliders affect balance, Mass affects how far it pushes the springs.

I havnt experimented much with adding colliders in random spots on my vehicles to see the results. I do have some vehicles with multiple box colliders, although they were probably evenly distributed, so might have not caused what you are seeing.

What sort of values are you using for mass, spring, etc

9

That won’t work. Modifying the spring strength in the Unity 5 WheelCollider doesn’t affect the suspension compression (yes, unrealistic but that’s how it works now…)

It doesn’t work that way in Unity 5 WheelCollider. Now the suspension is forced to be at the rest pose no matter the mass of the vehicle or the spring strength (see the posted link above).