[KenWittlief]

actully even feedback is not the perfect solution in this case - closed loop feedback requires an errror condition ( or signal) to build up to a certain point before it makes a correction

so using either wheel encoders or a yaw rate sensor you will still see some error to one side, until the error signal is big enough to apply the needed correction

our bot has the same problem - we use a yaw rate sensor to stay on heading, and it drifts right about 10° over a 2 second period, (while the error signal is building up and appying more and more 'left' command) then it goes straight as an arrow

we tweaked the desired heading in the SW and got it down to about 5° - but you cant get rid of it completely - so even with our gyro we have to point our bot about 5° to the left of where we want it to actully go.

It took us a couple matches to get the 'aim' down - but after that we were dead on target 100% of the time.

so the really easy solution is to leave your bot alone and figure out where you need to point it so it ends up where you want it.