Turn Adventurebot Using Angles

I am pretty new to working on the AdventureBot, and a class project requires me to make it turn at certain angles, such as turn left 55 degrees, turn right 34 degrees, etc. I have tried varying the speed of the left and right HDD motors, but to find an angle I have to do several tries to find the perfect setting, and repeat it for new values of angles. Also, the speed settings change with the surface of the floor. I do not seem to find a pattern in the left and right speed values either, through which I can write generic code for converting motor speeds to exact angles either for a particular surface.

Has anyone faced a similar problem? If yes, then how can I implement such an operation on AdventureBot? Is there a library or app that I can install on ARC?

Thanks