The Bionx System

The Bionx systems it not just a motor you put on a bike and it will run you around. It is a true electrical assist. It has a computer and will only applies power to the rear wheel while one is pedaling the bike. It senses the amount of torque one applies to the wheel through the petals and compares it to the speed one is traveling and then applies additional power to the wheel motor, when the bike reaches the speed to program wants the bike to be moving based on the torque on the wheel the motor applies less and less power until it is not doing anything.
The Bionx has a speed limiter and reduces it assist at 19.5 mph and stops completely at 20 mph. The system is configurable. It can add as much as 350 watts of power to the wheel motor. Most people of any reasonable fitness can produce about 300 watts of power on a bicycle and can sustain about 200 watts output for a long time depending on their level of fitness. The Bionx has four levels of assist. Level One adds up to 35% of additional power to what the cyclist is applying to the pedals. If the cyclist is applying 100 watts of power to the bike the Bionx would add up to 35 additional watts. The important point here is 'up to' - the assist does not just add 35 more watts but based on the torque applied by the cycles the Bionx will add just enough to move the bike at the speed the Bionx thinks it should be moving based on the torque on the wheel. Therefore the amount of assist is constantly changing based on the speed of the bike, the torque applied to the wheel and the assist level set at the console by the cyclist. As I said before there are four levels of assist and they all work the some way except they apply more or less assist base on the level. Level Two adds up to 75% assist, level Three adds up to 150% assist and level Four adds up to 300% assist.
The Bionx has another feature that is especially useful to trikes. When the keyed brake is applied the Bionx switched to generation mode. This turn the motor into a generator and recharges the battery but also slows down the bike acting as a brake - since all tadpole styles trikes I have seen do not have a rear brake this it very useful when descending because there is no brake induced steering which can occur during descents when using the front brakes.
This system is expensive and adds 15 pounds to the bike but it lets me climb hill faster than 2 mph and that help me keep up with others cyclist.