This application was created by me using appinventor. Maybe, in the future I will post a tutorial on how the app was made.
How the app works.
Simple. It just sends when a button is pressed a character over the serial port.

Also there are some special features
Remote control Interface
Vibration
Sounds when buttons are pressed
Front lights and back lights buttons
Three Function buttons for custom use
Panel showing the command send to the Bluetooth
Link to web page with detailed instructions
Arduino code provided
Speed control