How can I calculate voltage drop on non resistors?
Welcome to electronics!   Every challenge in this field starts with
this question, or something very similar.

A resistor has a known voltage/current relationship, and different
resistors all have the SAME relationship, just with a different
scale constant (which we call 'resistance value').   Similarly,
a battery, or motor, or capacitor, or transformer, can be characterized
by a mathematical model.

Some of these models are complex (for a motor, it has to include inertia, work done
on the load, internal wiring resistance, and possibly a half dozen other
variables), but all will boil down to equations.

Then, with a system of five components, there are five or more equations,
all simultaneously true.   This sounds complex (because it is, in more
senses than one), but it gets MORE complex when we come to the next step:
solve all the equations simultaneously,  There are mechanical methods for doing
this, and shortcuts, but those are never perfect.   The fact is that we can
always solve such a system IF it can be built; no real device ever
divides by zero, or does anything else that mathematics cannot handle.