The inputs are just some random numbers. You can use any numbers.
I am sorry I mentioned (4, -2, 7, 5, 11, 1) and then used (4, -2, 3.5, 5, -11, -4.6). This is just a mistake.
But you can try any set of inputs and it will work.
The RPi is connected and powered by a USB cable connected to the computer which feeds power to the motors.
Glad your issue is solved.
Yes each client is communicating with the server independently from other clients.
Sure, you may open a thread for each user rathe than handling all users on a single thread.
There is a common issue where the app is not given the permission to access the media files. Could you check the app settings for permission?
