MovePosition and IsKinematic causes rigidbody to float away forever

Unity Engine
1

On rare occasions, a character in my game will start to float away… The following code replicates the problem:

var pos = rigidBody.position;
pos.y += 0.01f;
rigidBody.MovePosition(pos);
rigidBody.velocity = Vector2.zero;
rigidBody.isKinematic = true;

Any ideas why? I’m using both MovePosition and isKinematic at different points in my game, so sometimes that will cause a character to float away…

2

Hi,

I’m bit perplexed. So this example code is what causes problems or is just what the problem looks like?

The code does mostly what I’d expect it to do. I think MovePosition sort of overrides setting velocity directly → Removing MovePosition will stop movement up, otherwise this movement is applied, no matter if you call the MovePosition in Update, LateUpdate or FixedUpdate, MovePosition seems to override setting velocity.zero.

3

If it would happen inside of Update, it would be no surprise. But a single call to a method containing that code will cause the character to float as well.

The code above shows what the problem looks like. I don’t use that code in 1 method. However, in rare occasions my game will try to apply moveposition and iskinematic to the same character at the same time, which will cause that character to float away forever.

Edit:
So, perhaps an example will help in this case :slight_smile:

Suppose the code above is inside a method called “Test()”, and a UI button will perform “Test()” on button click. In this case, clicking the button once will cause the character to float away forever.

4

Ah, OK. I haven’t noticed such behavior, but then again I don’t have that much experience scripting Unity Physics.

5

Check this out: 5.0.2f Rigidbody2D MovePosition setting the velocity now? - Unity Engine - Unity Discussions

I also think that MovePosition does not IMMEDIATELY move the object - it just tells the object how much to move the next time it gets around to moving. Combine this with the bug mentioned in the linked thread, and you have a situation where MovePosition laughs at your attempts to control an object’s velocity manually.