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 a rubber pneumatic tube tire. The rim has a 4 bolt pattern so you can easily mount it to a flanged hub.
This small synchronous switching step-down (or buck) regulator takes an input voltage of up to 38 V and efficiently reduces it to 5 V. The board measures only 0.7″ × 0.8″, but it allows a typical continuous output current of up to 5 A.