Imperfections of Robots

While attempting to get my robot to drive in a rectangle, I encountered a number of problems. The main problem I encountered was with getting my robot to go in a straight line. To correct this, I had to change the power level in one of the motors because it seemed to run slower than the other. I also had trouble getting the turn to be an exact 90 degrees. There was not enough variability in the set times. I was not able to get my car to turn 90 degrees by simply letting it go for 0.7 seconds. It was always either a little over or a little under 90 degrees, no matter what i adjusted. In order to solve these two large problems involving distances traveled over time, I think that we would have to disregard time entirely, as it is not accurate. Instead, we could use the number of rotations of the motor and axis.