What is the method for organizing object bodies (parent/child) in Cannon.js?

Question

What is the method for organizing object bodies (parent/child) in Cannon.js?

After extensively searching and reviewing issues and documentation, it seems that apart from establishing a constraint between two Cannon bodies, there is no direct method to unite shapes of varying masses.

Currently, I am using the lockConstraint approach, but I consider it to be a temporary solution. Occasionally, when my object collides, the rotation of the "child" object abruptly shifts to an unintended position...

Is there a more appropriate way to accomplish this?

Edit: My goal is to create a vehicle with the center of mass aligned with the center of the 4 wheels. To achieve this, I have set up a body with .collisionResponse set to 0 and the desired mass, positioning it at the center of the wheels. Subsequently, I establish the chassis with minimal mass and a new

CANNON.LockConstraint(chassisBody, mass, 0.5)

to effectively link the two objects together.

javascript three.js cannon.js

Answer 1

Answer №1

In Cannon.js, it is not possible to set mass/density per Shape directly. However, a workaround is to adjust the center of mass to achieve a similar effect.

Consider the example of a hammer, where the head is denser than the shaft. When a hammer is thrown, it rotates around a point close to its head due to the weight distribution.

To create a hammer in cannon.js, you can utilize two boxes:

var head = new CANNON.Box(new CANNON.Vec3(2,1,1));
var shaft = new CANNON.Box(new CANNON.Vec3(0.5,3,0.5));

To combine these shapes into a single Body, you can do the following:

var body = new CANNON.Body({ mass: 1 });
body.addShape(shaft, shaftPosition);
body.addShape(head, headPosition);

By adjusting the shape positions (shaftPosition, headPosition), you can control their position within the Body and the center of mass, affecting the rotation behavior.

Experiment with different positions to find the optimal center of rotation for your shapes. The full signature of Body#addShape allows adding a transform to position the shapes:

body.addShape(shape, position, quaternion);

Answer 2

In Cannon.js, it is not possible to set mass/density per Shape directly. However, a workaround is to adjust the center of mass to achieve a similar effect.

Consider the example of a hammer, where the head is denser than the shaft. When a hammer is thrown, it rotates around a point close to its head due to the weight distribution.

To create a hammer in cannon.js, you can utilize two boxes:

var head = new CANNON.Box(new CANNON.Vec3(2,1,1));
var shaft = new CANNON.Box(new CANNON.Vec3(0.5,3,0.5));

To combine these shapes into a single Body, you can do the following:

var body = new CANNON.Body({ mass: 1 });
body.addShape(shaft, shaftPosition);
body.addShape(head, headPosition);

By adjusting the shape positions (shaftPosition, headPosition), you can control their position within the Body and the center of mass, affecting the rotation behavior.

Experiment with different positions to find the optimal center of rotation for your shapes. The full signature of Body#addShape allows adding a transform to position the shapes:

body.addShape(shape, position, quaternion);

What is the method for organizing object bodies (parent/child) in Cannon.js?

Answer №1

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