sorry i dint reply sooner,
the pins were wired from gpio 19 , 16 , 26 , 20 (pins 35,36,37,38) to the 4 motor control pins (not the jumper pins as i have seen on some other methods)
also the GND (pin 6) was connected the the common GND terminal where the battery's gnd was connected. The motors are 100rpm 12v geared motors and the battery is a 11.1v 3s 8c lipo battery. The pi was powered by an anker 10400 powerbank through usb. I have seen on other forums about flyback current / voltage and the need for flyback diodes. Im not sure if the board im using has these. Is this a possible cause for frying my pi?