Using Rigidbody and Articulation Body on a same GameObject

Unity Engine
1

Hi guys,

I need to simulate mining machinaries such as excavator and drill rig which has tracks and arm.

Using Articulation Body I can simulate the arm movement nicely. Meanwhile, using rigidbody and wheel collider I can simulate tramming. However when I place all three articulation body, rigidbody and wheel collider on the same gameObject, wheel collider does not work.

Do you guys have any idea? What is the best way to simulate this kind of machinary?

2

I managed to work around by separating the arm and the body of the machine and added articulation body and rigidbody to them respectively. I also added fixed joint to the body and connect it to the arm. However the whole gameobject is shaking when I enter Play Mode.

3

Hey James, we are also working on a drill rig and have recently migrated our project to Unity 2020 so that we can use the articulation bodies for the drill arm movement. But we are running into issues when moving the arm up and down it will only go down ( due to the gravity pulling it down), we kept the stiffness of the body that goes up/down at 10000 as it gives the arm a weight distribution effect (jiggle effect). We have tested increasing the stiffness of the body higher, this does solve the issue of only moving the arm down but then we lose the jiggle effect that we want. Do you have any suggestions as to solve our issue without compromising the jiggle effect? How did you do the arm movement to achieve a simulated jiggle effect?

this is the code we are currently using to move the joints.

private float CurrentPrimaryAxisRotation(ArticulationBody articulation)
{
float currentRotationRads = articulation.jointPosition[0];
float currentRotation = Mathf.Rad2Deg * currentRotationRads;
return currentRotation;
}

private void RotateTo(float primaryAxisRotation, ArticulationBody articulation)
{
var drive = articulation.xDrive;
drive.target = primaryAxisRotation;
articulation.xDrive = drive;
}

float rotationChange = comp.pinvalue * comp.speed * Time.fixedDeltaTime;//RotationState can be pin value
float rotationGoal = CurrentPrimaryAxisRotation(comp.joint) + rotationChange;
RotateTo(rotationGoal, comp.joint);

4

Hi Kenmuir,

Just so you know I am very new to Unity Articulation Body, so I might not answer your question very well.

In my case, when I implement articulation body on more children joint I do get the inertia effect. For instance, if you have a game object hierarchy such as go1 → go2 → go3, if you implemented articulation body on go1(root) and go2 you will not get inertia effect on go3. However if you also implement articulation body on go3 then you will get the inertial effect.

Hope this help. Please let me know if I am wrong. Thanks!

5

I found the cause, the game object is continuously jittering because I set the suspension distance to 0. After I adjust a tiny suspension distance for the game object, it stops jitter.