ELEGOO Tumbller Self-balancing Robot Car - Stability test 

Amazing

It's very stable. Are you using encoders on the motors?

I have this exact model. The robot balance fine, but I can't make the Android phone app to work. It connects and that is it. Any suggestions? Also, I found some 6-7 years old software and APP for the phone on Github. But it doesn't work eighter. Thanks!