The project as originally conceived works great! Now, what was wrong with that design and how could it be improved?
The web page was great before I had the app but I've not used it once since. That seems to have been a dead-end.
Two other things come to mind...
1) The current design requires both the car and the tablet or phone be connected to the local WiFi network. Adjusting the phone is easy and not a problem. Adjusting the car requires changing the program, then a recompile and reload. Not too convenient.
2) The current design uses an app. How about hardware with a joystick, for instance, to control the car? That's another idea.
Two improvements to consider and perhaps work on.