Getting contact force on impact?

JCorvinus 2017-11-19 21:00:48 UTC #1

I'm trying to create a punch-able object that responds dynamically to how hard you hit it. Since the object can behave quite wildly after being hit, I'm really only interested in the impact force, not what kind of velocity happens afterwards. I tried hooking into the OnPerControllerContactBegin event and then getting the controller's velocity but it was zero?

After manually tracking the InteractionHand.velocity value, it seems to always be zero unless the hand isn't tracking? At that point it goes to a single non-zero value and stays there until the hand starts tracking again. Very strange. Anyways, any suggestions on how to get the impact force of a hand or controller would be awesome.

nbenson 2017-11-21 18:43:15 UTC #2

This is a pretty silly bug that we have in IE 1.1 currently and was fixed in our develop branch for future releases. The fix is embarrassingly simple:

public override Vector3 velocity {
  get { return isTracked ? Vector3.zero : leapHand.PalmVelocity.ToVector3(); }
}

Should in fact be:

public override Vector3 velocity {
  get { return isTracked ? leapHand.PalmVelocity.ToVector3() : Vector3.zero; }
}

github.com

leapmotion/UnityModules/blob/master/Assets/LeapMotion/Modules/InteractionEngine/Scripts/InteractionHand.cs#L241


      case HandDataMode.Custom: default:
        return _lastCustomHandWasLeft;
    }
  }
}


/// <summary>
/// Gets the velocity of the underlying tracked Leap hand.
/// </summary>
public override Vector3 velocity {
  get { return isTracked ? Vector3.zero : leapHand.PalmVelocity.ToVector3(); }
}


/// <summary>
/// Gets the controller type of this InteractionControllerBase. InteractionHands
/// are Interaction Engine controllers implemented over Leap hands.
/// </summary>
public override ControllerType controllerType {
  get { return ControllerType.Hand; }
}

If you need a smoother velocity, I like to use a custom script to fill a DeltaBuffer(5) (a data structure included in Core) with hand.PalmPosition values; when the buffer IsFull you can call Delta() on it to get the average velocity of the sample positions over the length of the buffer (in this case, five frames).