diff --git a/actor.py b/actor.py
index e809a85..72f51f9 100644
--- a/actor.py
+++ b/actor.py
@@ -1,43 +1,39 @@
 ###########################################
 # Created on 1-9-2013. Miguel Angel Astor #
 ###########################################
+import math
+
 import pygame
-from animation import Animation
+
+import math_utils
 
 ACTOR_STATES = { 'IDLE': 0, 'MOVING': 1 }
 
-class BaseActor:
-    """ Represents any game object. This is the parent class for the actor 
-    category of objects. It's behaviors are empty. """
-    def __init__(self, name, visible, solid, position):
-        """ Initializes the actor object. """
-        # Conditions and parameters.
+class BaseActor(pygame.sprite.Sprite):
+    def __init__(self, id, image, name = "Default", animated = False, visible = True, solid = True):
+        super(Sprite, self).__init__()
+        
+        self.id = id
         self.name = name
-        self.alive = True       # The Actor should be updated.
-        self.animated = False   # The Actor has animations.
-        self.visible = visible  # The Actor should be rendered.
-        self.solid = solid      # The actor can collide with other actors
-        # All sprites for an actor are stored as a list of pygame sprites.
-        # The list starts empty. Sprites must be added with the add_sprite method.
-        self.sprites = []
-        # Animations are stored as a key (Animation angle),
-        # value (Animation object) pairs. Animations are added with the
-        # add_animation method.
-        self.animations = {}
-        # Parameters for direction and movement.
-        self.position = list(position)
-        self.speed = [0, 0]         # [X speed, Y speed].
-        self.max_speed = [100, 100] # 100 pixels per second.
-        self.acceleration = [0, 0]  # Ditto.
-        # Collision detection information. AABB and Bounding circle.
-        self.b_box = [0, 0] # [X length, Y length].
-        self.radius = 0.0
-        # Parameters for rendering.
-        self.angle = 0
-        self.scale = 1.0
+        self.animated = animated
+        self.visible = visible
+        self.solid = solid
 
-    def is_alive(self):
-        return self.alive
+        self.angle = 0.0
+        self.position = [0, 0]
+        self.velocity = [0, 0]
+        self.acceleration = [0, 0]
+        self.max_velocity = [0, 0]
+        self.friction = 1.0
+
+        self.image = image
+        self.rect = self.image.get_rect()
+
+    def get_id(self):
+        return self.id
+
+    def get_name(self):
+        return self.name
 
     def is_animated(self):
         return self.animated
@@ -48,19 +44,70 @@ class BaseActor:
     def is_solid(self):
         return self.solid
 
-    def destroy(self):
-        self.alive = False
+    def get_position(self):
+        return self.position
 
-    def set_visible(self, visible):
-        self.visible = visible
+    def set_position(self, new_pos):
+        self.position = list(new_pos)
 
-    def toggle_visible(self):
-        self.visible = not self.visible
+    def get_velocity(self):
+        return self.get_velocity
 
-    def set_solid(self, solid):
-        self.solid = solid
+    def set_velocity(self, new_vel):
+        self.velocity = list(new_vel)
 
-    def toggle_solid(self):
-        self.solid = not self.solid
+    def get_acceleration(self):
+        return self.acceleration
 
-    def add_sprite(self, filename)
+    def set_acceleration(self, new_accel):
+        self.acceleration = list(new_accel)
+
+    def get_max_velocity(self):
+        return self.max_velocity
+
+    def set_max_velocity(self, max_vel):
+        self.max_velocity = list(max_vel)
+
+    def get_friction(self):
+        return self.get_friction
+
+    def set_friction(self, new_friction):
+        self.friction = new_friction
+
+class BulletActor(BaseActor):
+    """ Actor class with fixed velocity bullet behavior. """
+    def __init__(self, id, image, name = "Default", animated = False, visible = True, solid = True, frame_rate = 60):
+        super(BaseActor, self).__init__(id, image, name, animated, visible, solid)
+        self.then = 0
+        self.now = 0
+        self.frame_rate = frame_rate
+        self.moving = False
+
+    def is_moving(self):
+        return self.moving
+
+    def move(self):
+        self.moving = True
+
+    def stop(self):
+        self.moving = False
+
+    def update(self):
+        # Calculate the time elapsed between the previous call to update and this one.
+        self.now = pygame.time.get_ticks()
+        delta_t = self.now - self.then
+        if delta_t < 0:
+            delta_t = 0 # Compensatefor overflow of self.now
+
+        if self.moving:
+            # Then we update it's velocity components compensating for time.
+            self.velocity[0] += (self.velocity[0] * delta_t) * (self.frame_rate / 1000)
+            self.velocity[1] += (self.velocity[1] * delta_t) * (self.frame_rate / 1000)
+        # Finally we take friction into account.
+        self.velocity[0] *= self.friction
+        self.velocity[1] *= self.friction
+
+        # TODO: Update animation frame if any.
+
+        self.then = self.now
+        
diff --git a/animation.py b/animation.py
index 351f26c..f3cc635 100644
--- a/animation.py
+++ b/animation.py
@@ -3,15 +3,15 @@
 ###########################################
 
 class Animation:
-    """ This class represents an animated sprite. No sprite information is
-        stored in this class, only sprite indexes. """
-    def __init__(self, name):
+    """ This class represents an animated sprite. """
+    def __init__(self, name = "Default", num_frames = 1, frame_start_offset = 0):
         """ Initializes an empty animation. """
         self.fps = 0
         self.name = name
         self.looping = False
+        self.frame_start = frame_start_offset
+        self.num_frames = num_frames
         self.current_frame = 0
-        self.frames = []
 
     def __str__(self):
         """ Returns a string representation of this animation. """
@@ -19,30 +19,11 @@ class Animation:
                " :: Looping : " + str(self.looping) + " :: Current frame: " +
                str(self.current_frame)
 
-    def add_frame(self, frame):
-        """ Adds a frame to this animation. Frames should be added in order. """
-        self.frames.append(frame)
-
-    def get_next_frame(self):
-        """ Returns the current frame of the animation. Moves the current frame
-            count by one. """
-        if(self.looping):
-            self.current_frame = (self.current_frame + 1) % len(self.frames)
-        elif (self.current_frame == len(self.frames) - 1):
-            pass
-        return self.frames[self.current_frame]
-
     def get_current_frame(self):
         """ Returns the current frame of the animation. """
         return self.current_frame
 
-    def set_current_frame(self, frame):
-        """ Changes the current frame of the animation. """
-        # The frame is wrapped modulo the number of frames to ensure it is valid.
-        self.current_frame = frame % len(self.frames)
-
     def get_looping(self):
-        """ Returns wether this animation should loop or not. """
         return self.looping
 
     def set_looping(self, looping):
@@ -53,3 +34,10 @@ class Animation:
 
     def set_frames_per_second(self, fps):
         self.fps = fps
+
+    def generate_animation(self):
+        """ Generator function that returns the next frame of the animation. """
+        while True:
+            for frame in range(self.frame_start, self.frame_start + self.num_frames):
+                self.current_frame = frame - self.frame_start
+                yield frame
diff --git a/math_utils.py b/math_utils.py
new file mode 100644
index 0000000..8ddfd2f
--- /dev/null
+++ b/math_utils.py
@@ -0,0 +1,6 @@
+###########################################
+# Created on 1-9-2013. Miguel Angel Astor #
+###########################################
+
+def angle_to_vector(angle):
+    return [math.cos(angle), math.sin(angle)]