1) We need to know what is the goal of your App Inventor App - what is it going to do? Control a Robot?
A: I have a old machine, it's controller is not work good. I wish replace it by plc<--wifi-->smart phone<--cable or bluetooth-->joystick.
Smart phone is good choices because of its weight, battery time, and have a screen to show some information of plc.
2) The Joy Stick - is it an FTC Game Pad? If not, tell us what it is, with a link to the manufacturer's website for technical details.
A: No it's not FTC Game Pad. It's manufacturer's show below:
I also consider connect joystick and smart phone by Bluetooth. But the USB method is the most expensive way.
I found another way to use USB joystick.
I created a apk with some buttons. And use joystick's app connect to joystick. Then mapping joystick's buttons to this buttons of my app. So I don't need to process USB joysticks' communication.
It's also work by Bluetooth joystick.
But In this way,I should keep my screen always on.