This is a robot drive wheel we had made specifically for us. It does not have a bearing. Its 6 inches in diameter. 1.9" inches wide. Its foam filled with a 4 bolt pattern so you can easily mount it to a flanged hub.
These Planetary Gearboxes are nominally 32mm in diameter with permanent magnet reversible DC motors. We carry 12VDC and 24VDC motors and range from 8 to 265 RPM. Several right angle gearboxes. Several motors have encoders.
These tiny gearmotors are available in a range of gear ratios. All of the micro metal gearmotors have the same physical dimensions, so one version can be easily swapped for another if your design requirements change.