The two most common types of hub motors used in electric bicycles are brushed and brushless. Many configurations are available, varying in cost and complexity; direct-drive and geared motor units are both used. An electric power-assist system may be added to almost any pedal cycle using chain drive, belt drive, hub motors or friction drive. BLDC hub motors are a common modern design. The motor is built into the wheel hub itself, and the stator fixed solidly to the axle, and the magnets attached to and rotating with the wheel. The bicycle wheel hub is the motor. The power levels of motors used are influenced by available legal categories and are often, but not always limited to under 750 watts.

Speed Pedelec ebikes – A new classification of bikes called ‘Speed Pedelecs’ have emerged which technically meet the bicycle definition for a 20 mph ebike. These ebikes are designed to max out at 28 mph. Pedelecs are pedal activated vs throttle activated. The weasel words within the definition says, “20mph on motor alone”. Thus, a person who adds their leg power to the motor assist and happens to cruise at 28mph is NOT doing it by motor alone, and therefore the bike is considered to be compliant with the Federal Law. If the rider stops pedaling, the speed pedelec cannot maintain speed. Speed Pedelecs are becoming more popular in Europe and America, which means more models are being offered.
Whether the terrain is flat or hilly impacts the distance you can travel, as does the weight of the bike, your own weight, the gearing available on the bike, and how much juice you give it. We suggest that a distance of 10 to 20 miles is a realistic expectation. Of course, if you're prepared to do at least some pedaling, you can extend that dramatically.
In a parallel hybrid motorized bicycle, such as the aforementioned 1897 invention by Hosea W. Libbey, human and motor inputs are mechanically coupled either in the bottom bracket, the rear or the front wheel, whereas in a (mechanical) series hybrid cycle, the human and motor inputs are coupled through differential gearing. In an (electronic) series hybrid cycle, human power is converted into electricity and is fed directly into the motor and mostly additional electricity is supplied from a battery.
On the other hand, the battery doesn’t lock into the bike, which means you can’t just leave it on your bike when you park at the bike rack. Anyone could walk by and simply remove your battery. That seems like an oversight to me, though perhaps the designers assumed that such a small battery would just be easy to take with you. And it is. My wife could probably lose this battery in her purse.