[mikets]

Thanks Andrew. In the past, I have seen a lot of students wrote code that did trial and error. When the motors did not go the way they wished, they negate the power. For example, I've seen students doing tankDrive(0.5, -0.5) or tankDrive(-0.5, -0.5) just to go forward. They said as long as it works, it shouldn't matter. But eventually, the code became very confusing. So when I taught my students, I always tell them to test each individual motor by setting positive power and make sure they go forward by doing setInverted on motors that spin in the wrong direction. And in theory when all motors are going forward with positive power, there should never be negative value in any kind of drive: tankDrive, arcadeDrive and mecanumDrive, when going forward. If you have to negate the power, somebody screwed up. That's why I think RobotDrive class is wrong.