Rigidbody.MovePosition doesn't move reliably?

I don't know how to explain it to you. It's very hard to explain and my explanations sucks :/ But basiclly, what makes you rigidBody moving more or less than you desire is your "bIsSpinning". In this cases I advise you to use Mathf.Lerp

Try this:

 private Vector3 oldPos;
     
 private float timer;
 
 private bool setOldPositionAndRotation;
 
 if(bIsSpinning == true)
 {
     if(setOldPositionAndRotation == false)
     {
         setOldPositionAndRotation = true;
         oldPos = rigibody.position;
     }
 
     timer += Time.fixedDeltaTime;
 
     if(spinDirection == "right")
     {
         rigidbody.MovePosition(Mathf.Lerp(oldPos, oldPos + Vector3(30,0,0), timer));
     }
     else if(spinDirection == "left")
     {
         rigidbody.MovePosition(Mathf.Lerp(oldPos, oldPos + Vector3(-30,0,0), timer));
     }
     if(spinDirection == "up")
     {
         rigidbody.MovePosition(Mathf.Lerp(oldPos, oldPos + Vector3(0,-20,0), timer));
         
     }
     else if(spinDirection == "down")
     {
         rigidbody.MovePosition(Mathf.Lerp(oldPos, oldPos + Vector3(0,-20,0), timer * 3.0f));
     }
 }
 else 
 {
     setOldPositionAndRotation = false;
 
     timer = 0;
 }

I've done only for position. But for the rotation it is the same story.

Thanks for the reply! I tried your code, but I got a string of errors that all say

"The best overload for the method 'UnityEngine.Mathf.Lerp(float, float, float)' is not compatible with the argument list '(UnityEngine.Vector3, UnityEngine.Vector3, float)'"

or

"The best overload for the method 'UnityEngine.Rigidbody.MovePosition(UnityEngine.Vector3)' is not compatible with the argument list '(float)'"

Oh sorry my bad. I've should done this:

  private Vector3 oldPos;
      
  private float timer;
  
  private bool setOldPositionAndRotation;
  
  if(bIsSpinning == true)
  {
      if(setOldPositionAndRotation == false)
      {
          setOldPositionAndRotation = true;
          oldPos = rigibody.position;
      }
  
      timer += Time.fixedDeltaTime;
  
      if(spinDirection == "right")
      {
          rigidbody.MovePosition(new Vector3(Mathf.Lerp(oldPos.x, oldPos.x + 30, timer),rididbody.position.y,rididbody.position.z));
      }
      else if(spinDirection == "left")
      {
          rigidbody.MovePosition(new Vector3(Mathf.Lerp(oldPos.x, oldPos.x -30, timer),rididbody.position.y,rididbody.position.z));
      }
      if(spinDirection == "up")
      {
          rigidbody.MovePosition(new Vector3(rididbody.position.x,Mathf.Lerp(oldPos.y, oldPos.y -20, timer),rididbody.position.z));         
      }
      else if(spinDirection == "down")
      {
          rigidbody.MovePosition(new Vector3(rididbody.position.x,Mathf.Lerp(oldPos.y, oldPos.y -20, timer * 3.0f),rididbody.position.z));
      }
  }
  else 
  {
      setOldPositionAndRotation = false;
  
      timer = 0;
  }

This worked perfectly, thank you!