Mecanum Formation

i searched for this and didnt find a definitive answer that laid out all the differences in one spot so i would really like to ask the question.(if this has been posted please direct me to the correct thread because it was hiding from me)

On mecanums what is the proper wheel formation. I have seen pictures of bots with the where they form an โ€˜Xโ€™ and bots where they form a diamond with the rollers. What is the difference? advantages/disadvantages of each?:confused:

Thanks in Advance
Bill

This discussion canโ€™t happen unless we all agree on a frame of reference. If thereโ€™s an โ€˜Xโ€™ formed by rollers on the top of the wheels, thereโ€™s a diamond formed by the rollers on the bottom. Iโ€™ll talk about the shape formed on the bottom.

Both a diamond and an โ€˜Xโ€™ will allow you to achieve omnidirectional motion. An X, however, is not ideal because it offers no resistance to rotation from outside forces. That is โ€“ another robot could spin your robot around the intersection of the โ€˜Xโ€™.

A diamond, on the other hand, resists rotation from outside sources. This is what 99% of teams will want.

Check here:
http://www.firstroboticscanada.org/site/files/workshops/omnidirectional.pdf

Hope this answers most of your questions.