Power BJT Transistor in motor driver keeps burning
I am not the biggest expert on BJT's, but they are reliant on the current going into the base. The smaller part might require less current into the base for higher collector current. This explanation means that your big transistors never broke, they just never allowed enough current for the motor to move. 

You have 2 BJT where you need to figure out the current gain from the first stage, and calculate if this will be enough current for the second stage, to rotate the motor.

In any case I would get into the MOSFET world instead, they are much easier to use and understand. You can get away with measuring the voltages at the gate node, instead of measuring the current into the BJT gate.