The turning ability of a robot with no drop-center and all traction wheels is dependent on the normal force experienced at each wheel. That is to say, it depends on how much force each of the wheels on the robot supports.
As Jared mentioned in his post that was linked to, a 6 wheel drive with no drop center is statically indeterminant. This is because if you isolate the physics on one side of the drive train (assuming a perfectly symmetrical robot), you have the force for 3 wheels as variables but only the sum of moments about the wheels’ axes and the sum of forces in the vertical axis as equations. That’s 3 variables and 2 independent equations, so this mathematical model cannot solve for how much weight each of the wheels supports.
This makes it complicated to approach from a design perspective, which is why the over simplification of “a long wheel base robot without drop center wheels will not turn” is often made. In reality, as you approach the limit where all of the weight is supported by the 4 corner wheels, the robot will behave like a 4WD long robot and have difficulty turning. As more and more of the weight is supported by the center wheels, this reduces the normal force at the corners, thereby reducing the tractive force applied at the corners and reducing the robot’s resistance to turning. More weight at the corners = Harder turning. Less weight at the corners = Easier turning.
When the center wheel is dropped on a robot, much of the robot’s weight is supported by the center wheel at all times in addition to shortening the wheel base, which makes turning easier (another generalization, but a widely accurate one so this is part of why drop centers are so popular).
Team 25 REALLY knows what they are doing, which is why they can pull this off. My guess would be that criteria that lead them to this type of design decision are:
-Makes it harder for defense to turn them
-Eliminates rocking, so stability isn’t an issue
I personally cannot perform the math necessary to prove that a drive train without a drop-center would turn. I also have not done the necessary testing and experimentation to have the experience needed to design such a drive train that I will guarantee can turn well. Therefore, I would hesitate to build this type of drive train. This is where it’s important for teams to build within their means and recognize them.