"Do your own balance car" can only use torque (Nm) but the tutorial is all voltage. How to convert?
You can convert Power into torque.

To get from Voltage to Power, you need to know the current and efficiency of the engine.

The Power (that you can convert) will be Voltage  x Current x Power-Factor (which is always under 1).

Example: at 24V, 20A current and 0.9 efficiency factor you have a power of 24x20x0.9 = 243W.

Now sicne you have the power, you use Power (kW) = Torque (N.m) x Speed (RPM) / 9.5488 to get to your torque.