Add bee-bot / turtle robot example, close #443

docs/examples/robot_buttons_2.py

@@ -0,0 +1,34 @@
+from gpiozero import Button, Robot
+from time import sleep
+from signal import pause
+
+robot = Robot((17, 18), (22, 23))
+
+left = Button(2)
+right = Button(3)
+forward = Button(4)
+backward = Button(5)
+go = Button(6)
+
+instructions = []
+
+def add_instruction(btn):
+    instructions.append({
+        left:     (-1, 1),
+        right:    (1, -1),
+        forward:  (1, 1),
+        backward: (-1, -1),
+    }[btn])
+
+def do_instructions():
+    instructions.append((0, 0))
+    robot.source_delay = 0.5
+    robot.source = instructions
+    sleep(robot.source_delay * len(instructions))
+    del instructions[:]
+
+go.when_pressed = do_instructions
+for button in (left, right, forward, backward):
+    button.when_pressed = add_instruction
+
+pause()

docs/recipes.rst

@@ -331,8 +331,12 @@ Button controlled robot
 
 Use four GPIO buttons as forward/back/left/right controls for a robot:
 
-.. literalinclude:: examples/robot_buttons.py
+.. literalinclude:: examples/robot_buttons_1.py
 
+Alternatively, use four buttons to program the directions and add a fifth
+button to process them in turn, like a Bee-Bot or Turtle robot.
+
+.. literalinclude:: examples/robot_buttons_2.py
 
 Keyboard controlled robot
 =========================