Let me show you the app that I use for most of my LEGO RC stuff – the great BrickController 2 created by Istvan Murvai.
You can control almost anything you have:
all of these with an Android compatible gamepad! I use the ipega PG-9025, it is tested and working well with the application.
You can download the app from the Android Play Store here. An iOS version is currently under development, will let you know once it is released.