Re: pic: Lightweight 8 CIM Shifting Swerve Drive Chassis
 

What makes you think that?

Re: pic: Lightweight 8 CIM Shifting Swerve Drive Chassis
 

Each wheel is independently steered, and if you had a 6 CIM 4WD tank that was 21" by 35", it would be able to turn in place without too much trouble.

This drive would be able to turn in place or translate without any scrubbing. It wouldn't have any resistance until it turned while driving. I think this relatively small disadvantage would be outweighed by the advantage in a pushing and driving straight.

Re: pic: Lightweight 8 CIM Shifting Swerve Drive Chassis
 

It sounds like you just moved the goalposts. But perhaps I am misunderstanding. Are you still saying that it "would be able to do any swerve movement with a little scrubbing" ?

Re: pic: Lightweight 8 CIM Shifting Swerve Drive Chassis
 

Yes my intent was to support that claim. The only time scrubbing would be involved is when translating arbitrarily, and rorating at the same time. I believe that in that case, the 6 CIMs would be able to power though the scrubbing, given the gear ratio and width/length of the drive base.

Obviously, this is an opinion, and you can be sure without testing.

Re: pic: Lightweight 8 CIM Shifting Swerve Drive Chassis
 

What wheel angles and wheel speeds would you use to make that bot pivot around, say, the front left wheel? (a common swerve maneuver).

Re: pic: Lightweight 8 CIM Shifting Swerve Drive Chassis
 

I would not call this a "common swerve maneuver" as I have only ever seen one robot get notable benefit from using it. Turning around one wheel is the worst case scenario for a swerve with front and back wheels tied because two wheels on the same side should ideally have a large speed differential.
Regardless, It should be possible to perform this maneuver with something like this:
https://scontent-a-sea.xx.fbcdn.net/...2a&oe=54DF1511
(and a lot of scrubbing)

Re: pic: Lightweight 8 CIM Shifting Swerve Drive Chassis
 

Rotating around a point other than the Center of Geometry of the robot is a very basic swerve maneuver.

Indeed. I choose the front left wheel as the Center of Rotation to simplify the problem statement, and to pick an extreme case to try to clarify what you meant by "do any swerve movement".

If you are interested in exploring the physics of "scrubbing swerve", I invite you to participate (or just read along) here.