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c#unity-game-enginegame-physicsrigid-bodies
John Doe
John Doe

Reputation: 31

Rigidbody falling speed resets when moving midair

So my rigidbody controller has a speed limiter with the following code:

 Vector3 flatVel = new Vector3(rb.velocity.x, 0f, rb.velocity.z);
 // limit velocity if needed
 if (flatVel.magnitude > moveSpeed)
 {
  Vector3 limitedVel = flatVel.normalized * moveSpeed;
  rb.velocity = new Vector3(limitedVel.x, rb.velocity.y, limitedVel.z);
 }

but for some reason that last line of code:

rb.velocity = new Vector3(limitedVel.x, rb.velocity.y, limitedVel.z);

causes my character's falling speed to reset when moving in midair, when it reaches about -50 units of speed. I've tried modifiying rb.velocity.x and rb.velocity.z seperately, but Unity doesn't allow that. Is there any other way to cap rigidbody speeds without using rb.velocity?

Upvotes: 0

Views: 167

Answers (1)

RStevoUK
RStevoUK

Reputation: 456

According to the Unity documentation here.

In most cases you should not modify the velocity directly, as this can result in unrealistic behaviour - use AddForce instead Do not set the velocity of an object every physics step, this will lead to unrealistic physics simulation. A typical usage is where you would change the velocity is when jumping in a first person shooter, because you want an immediate change in velocity.

I'd say this is the reason you are encountering the behaviour that you are.

A Unity forum post, found here, suggests the correct way to do this is:

The 'proper' way would be to apply a force in the opposite direction of the rigidbody's velocity. The amount of force should be proportional to the extent to which the rigidbody is exceeding its speed limit.

Another Unity forum post suggests to make use of the ClampMagnitude method, the post can be found here.

private void FixedUpdate()
{
    var force = new Vector3(input.x, 0f, input.y) * acceleration;
    var velocity = playerRigidbody.velocity + force;
    playerRigidbody.velocity = Vector3.ClampMagnitude(velocity, maxSpeed);
}

Hope this helps.

Upvotes: 1

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