No potential across output of H-bridge I’m working on a robot with a club at my school. So far, our team has an H-bridge shield (https://www.freetronics.com.au/products/hbridge-dual-channel-h-bridge-motor-driver-shield#.WwI9omh_WEc) to drive motors in a toy tank. The H-bridge is powered by 6 AA batteries and the arduino is powered through the H-bridge shield with these batteries also. 
 When everything is connected up and  code uploaded to make the motors run forward, nothing happens - the motors don’t run. So far to debug, I’ve used a multimeter to check the voltages being output to the H-bridge from the arduino controller. These are all as expected. I’ve touched the motors to the positive and negative terminals of the battery and they run as expected. Lastly, I’ve substituted the H-bridge shield for a known working one. This did not fix the problem. I disconnected the motors and tested the voltage being output, which measured as +6V for both terminals of the motor relative to the negative terminal of the battery as well as relative to the ground pin. I also disconnected the jumper powering the arduino from the H-bridge shield and instead powered the arduino from my laptop. This did not fix the problem either. This seems completely contradictory. Any ideas on what the problem could be? Thanks so much ❤️❤️
It sounds either (i) like your motor driver is broken or (ii) your code does not operate the H bridge properly.  Check which digital outputs pins of the Arduino control the H bridge and make sure that they do not short out the H bridge.

If you want to try another H bridge, this one is suitable for your application: https://www.pololu.com/product/2990 .  I have worked with this before and it's very easy to use.