You need to root your device.
Also, you need to have and install the following:
1. USB/BT Joy Center
1. USB hub with power capability
2. your generic gamepad
3. USB OTG
- After the installation of the APK Insert your hub with power capability (some tablets and phones cant give enough power to the joystick).
- When the USB hub lights up it is detected by the tab, all you need to do is plug your generic gamepad.
- Now open USB/BT Joy Center this software will automatically detect your gamepad.
- (trouble shooting) when your device is not detected. Restart your device with all the hardware connected.
- When your tab is already open, try reopening USB/BT Joy Center. I think this should do the trick.