Physics Setup

The handling of the bus is influenced by the Physics asset of the bus. The main factors are the weight of colliders and their influence on the center of mass of the bus.

Weight

The weight is setup in the physics asset. Each collider added to the bus will increase its weight, unreal automatically calculates a default weight depending on the size of the collider. If you think the recalculated weight is not right, you can check the MassInKG checkbox when you select a bone and type in your own weight.

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Center Of Gravity

The center of mass influences how the bus leans in curves, if it is to high up it might cause the bus to be prone to tip over, if it is to low it might lean in the wrong direction.

The center of mass of the bus is automatically calculated by taking all colliders and collider weights into account, but there are 2 ways to affect it:

1. Disable the Contribute to Mass Checkbox on colliders that should not influnce the center of mass. You will see the center of mass move if you active the Mass property flag.

2. Add a Center of Mass Offset. This directly moves the center of mass in the desired direction. The offset is in centimetres, but you will not be able to see this change in the physics editor.

Open activate to see centers of mass for bus mesh

Fake Gravity

It might happen, that a bus can’t drive up a very steep hill or fully brake on a steep slope and continue to slide down. To alleviate that we added a “fake gravity“ feature. It basically helps the bus to stick to the street better at very low speeds giving it more grip for accelerating or braking. Check the “Fake Behaviour” in Movement Component of the bus. The External Curve defines how much the local gravity of the bus is changed depending on how steep the slope is.

Physics Override Data Asset

The Physics Override data asset gives us a centralized place to set driving settings as well as suspension setting. It is set on the Vehicle Movement component on the bus, and if you check the Allow Runtime Updates you can change this data asset while the game is running and you can test changes directly ingame.

Next Step

Customization