Our team has done 4 wheel independently drive, Independently steered, continuous rotation, co-axial swerve for the last 3 years. It has been quite an experience. So many little problems to solve. Do not underestimate the difficulty of getting a swerve to the point that it gives a competitive advantage. The risk of failure is very high. Our team after allot of debate decided that if we were going to take on the challenge and invest all the time effort and MONEY to develop swerve then we did not want a design with limitations. Thus we developed the unicorn version. Our first year we completed the mechanical but the software wasn't quite right. Our first regional was a little embarrassing. The robot had some moments when it had what I refer to as a grand mal seizure. The team called it the happy dance. We did solve the software issues for our next regional. And it performed well except we ran into the locking pin and Jag issue with the window motors we used for steering. From our first year the most important thing we learned was the difficult of repairing and servicing the system. While the wheel modules were independent, they were built into the frame. For our second year, We redesigned each wheel module to be total independent. If we have a problem We remove 4 bolts, disconnect 3 pairs of wires and remove the unit. Reverse the process with a pre-calibrated spare run a test and get on to the next match. With tying wheels together you are going to have a much more complex servicing task and you will most likely miss matches. It's a service nightmare in the pits. After our experience I would highly recommend a modular approach with independent modules. Take the time to perfect it.
One advantage with unicorn drive is that you can choose the location of the center point that the robot rotates around. In 2010 we had a mode were the robot rotated around the center point of the soccer ball making aiming easier. 2011 we used the same concept to rotate around the pole base to align the mini bot. Think carefully before you go down a swerve path with linked wheels. Team 1717 has posted their solution. This is a link to our solution.
http://wiki.team1640.com/index.php?t...II_Drive_Train