First of all I’d like to clarify that I am more or less a complete beginner when it comes to using shields with an Arduino.
I bought 2 of the aforementioned shields as I need to control 3 DC - Motors. The way I’ve put it together is shown in the image attached below.
Whereby the first shield is connected normally while the second one has its “10”, “9”, “8” pins connected to the Arduino Uno’s 5, 4, 3 pins respectively.
As expected the motors connected to the first shield runs normally, but I was wondering if there was a way to control the 3rd motor in a similar fashion to the first 2.
Additional notes: The first shield is powering the whole board as well as the second shield
It is difficult to tell from your pictures, but it looks like VCC is not being supplied with power, which is needed for the motor driver to operate. Are you able to control your motor after connecting VCC to 5V on your microcontroller? (Be sure to also connect GND to your microcontroller.)
You did not mention how you were trying to control the second shield, but in case it was not already clear: the DRV8835 library can only control two motors from a DRV8835 shield that is connected normally. To control your third motor, you can just use
analogWrite() on your new PWM pin (which looks like pin 5).
By the way, some of your soldered joints look like they might not be completely whetted. I recommend reading this soldering guide, and re-touching some of those soldered joints if they are not ideal.