diff --git a/script/local.py b/script/local.py
index facde69..376ce24 100644
--- a/script/local.py
+++ b/script/local.py
@@ -51,19 +51,23 @@ class RobotModbus(DeviceBase):
         try:           
             self.request()         
             ret = robot_ret.read()            
+            if ret == 1:
+                return True
+            if ret == 2:
+                raise Exception("Invalid command: " + str(command))                
+            raise Exception("Unknown error: " + str(ret)) 
         finally:
             self.cancel_request()
-        return ret
     
     def request(self):
         robot_req.write(1)
         while robot_ack.read() == 0:
-            time.sleep(0.01)
+            time.sleep(0.001)
 
     def cancel_request(self):
         robot_req.write(0)
         while robot_ack.read() == 1:
-            time.sleep(0.01)
+            time.sleep(0.001)
         
     def mount(self, puck, sample):
         return self.execute('1', '1', puck, sample)