If it’s not turning left or right but is able to move forward fine then it’s most likely a code issue. Could you please share the code you are using?
If you’re using the drive function on the brain, I believe that the correct motor port for the 2nd left side motor port is 9, and the 2nd right motor port is 10. You can double check by going inside drive and then going to the tab that’s called something to the like of wiring or motor ports. If you are using the drive function, I would also recommend trying to code your own programs, it’s not very hard.
Another issue could be that one of your motors are reversed incorrectly, which would make each side of the drivetrain counteract each other. The best way to check this is to pick your robot up and spin the drivetrain, as that can help you diagnose problems easier. Good luck!
Thank you all for your suggestions. We ended up switching the back wheel with the gear in front of it. Mechanical issue!
