Think of a circle like this:
The Robot Starts with it's wheels like this:
``U
__U__
Where the U's are the wheel, and the Lines the limits of movement. I'll use F to show which way the wheel is turning.
Please ignore the `'s, the're just for spacing.
The driver would start by driving forward 45 deg to the right:
````F
```U
__U__
Then All the way to the Right:
__UU_F
Then Back and to the right:
`U
__U__
```F
Then straight Down:
``U
__U__
``F
Then Down to the left:
```U
__U__
`F
Then All the way left:
F_UU___
And Finally, Up and left:
F
`U
__U__
So, you can get full motion with 180 degrees of pivoting. You just reverse the drive direction based on which side of the Y axis you're on (positive or negative).
Sure, you need to move the wheel back some to change your angle, but you'd have to do that anyway.
I'll post a link to a quick animation showing the bot doing a circle (3d sim) just in case you can't understand my little ASCII demonstration
