[apalrd]

Chain-less Mecanum:

Use AndyMark Toughboxes or Toughbox Nano's and mount the mecanum wheels on a hub, directly on the axle. Works well. Many teams that I saw did this (most mecanums I saw were direct drive), although I have no specifics. If you look at AndyMark's website, they have a drivetrain kit for 4-wheel direct-drive mecanum with toughboxes.


Nonadrive:
The creation of teams 148 and 217 (Robowranglers and Thunderchickens, respectively), it is a 9-wheel drive system essentially a convertible slide drive. Here is how it works:

There are four omni wheels on the perimeter of the robot, driven in standard tank drive. Each wheel is on a "pod" with a high-traction wheel, and the pods are pneumatically moved so the traction wheels can either provide traction or float above the ground.

In the middle there is a single omni wheel, driven by a single CIM, which is sideways (to cross the bumps, 148 and 217 pneumatically lifted this wheel a few inches to give them the center clearance necessary to cross the bumps).

This provides the "standard" amount of power (4 CIM's, or around 1.2 kw) in the forward/backward direction, while allowing non-pushing motion sideways. Since omni wheels are push-able, they can lower the perimeter wheels to push or avoid being pushed.