[Debugging] why is my velocity changing between Update() calls?

I have a problem with my movement "stuttering."

Code (csharp):

1.  Vector3old=isoRigidBody.velocity;
2. isoRigidBody.velocity=newVector3(2,0,0);
3. Debug.Log(old+"->"+isoRigidBody.velocity+"("+Time.time+")");

When I run this inside my update function, the log sometimes shows that the value is changing from some smaller value on some Update() calls, such as from (1.9,0,0) to (2,0,0).

I don't have any physics on my object, so I can't figure out why this is happening. I'm still fairly new to Unity and don't know what the potential causes are. I wanted to figure out how to set a memory breakpoint in MonoDevelop (so I could find out who's modifying the velocity variable between frames), but I can't find an elegant way to do this.

So, what's the best way to debug this issue?

 

You should try to not manually set the velocity of rigidbody. It produces unexpected results.
The manual even warns you not to do it:
http://docs.unity3d.com/ScriptReference/Rigidbody-velocity.html
You should use something like:
http://docs.unity3d.com/ScriptReference/Rigidbody.AddForce.html

 

To be fair, it says unrealistic results, not unexpected results.
@inZania can you try it while printing the vector elements manually? Like Debug.Log("Velocity = [{0}|{1}|{2}]", vel.x, vel.y, vel.z), as the vector3 -> string conversion does silly things to make it more readable.

 

It is unexpected results because if you set the velocity every update the rigidbody will eventually pass through walls and floors and other items with colliders, which is not expected behaviour of a rigidbody.

 

We do exactly that in Android game and see no issues. It's using RigidBody2D with gravity, physics and everything. You've had a programming mistake somewhere.

For original post, maybe the player is tripping on edges of floor colliders? Even if player feet are circle collider, a Y difference of 0.001 makes a corner for 2 box colliders and can cause a slight change in speed.

 

It turns out the materials were creating friction =P