[ebarker]

This is a topic that comes up every year.

Assuming that you have taken care of calibrating the Jaguars I will move on to the issue of 'motor bias'.

DC motors have a tendency to run a little faster in one direction than in the reverse direction. It is a nature of the beast.

Since you have at least two motors, one on each side of the robot, and they are turning in opposite directions relative to each other, there is the motor bias problem.

So if one side is turning CW, the other side is CCW. And one of those modes is faster than the other.

And all of this is assuming you have calibrated the Jaguars, and that you didn't build in a drivetrain defect into a transmission, like a draggy failed bearing, etc.

So even with calibrated Jag's, perfectly matched transmission, it will not go perfectly straight.