The main driving force, the inertia created by your eBike’s motor, is the energy that is stored in the battery. These two elements must be in perfect symbiosis with each other, and that would not be possible without an eBike controller.
The controller is responsible for switching the motor on and off at the precise millisecond for the smoothest riding experience. Ideally, this is what makes a well-designed eBike feel as if it’s in complete harmony with the rider’s physical effort.
Indeed, your eBike’s controller is similar to your computer’s CPU in that it will control input/output from different sources on your eBike:
- The dynamic loads on your bike e.g. rider weight & torque input, and climbing or descending etc.
- Throttle position (if present)
- Circuit protection from either too much amperage, voltage or heat
- PAS (pedal assist system)
- Brake applications
- Your speed
- Data from your electronic display
Pedal assist – combining your own power with your motor
What’s cool about pedal assist systems is the level of assist available. On certain models, there’s as many as 5 levels of assist on tap. So you can use as little as you like to maximize your battery’s range, or as much as you like to get up that steep hill. Or perhaps you’re doing some low-impact leg rehab after surgery or an injury. Pedal assist can ease you into this often long road ahead – by tailoring your own amount of effort, and the impact on joints or muscles. Getting out on the road is a lot more therapeutic than staring at the wall on a stationary bike or at the gym.
Among the things mentioned above, your eBike’s controller is reliant on the data that’s provided by the PAS (pedal assist system) sensor.
There are torque based PAS sensors, which is a more advanced technology out of the two main categories. Then there are classic cadence sensors.
What is a cadence sensor you say?
Basically, they measure the rate or tempo of your pedaling, and control your motor’s output accordingly. The cadence sensor provides the required power support via the controller, and ultimately your motor if you start pedaling faster. On some models, once you’ve created enough of your own inertia, e.g. a predetermined speed you’re comfortable riding at, your motor’s output will decrease. This is pretty neat. Not only will this PAS save your battery’s power, but also will prevent you gaining excessive speed too.
This is important. For example, in some countries an eBike’s maximum speed can be just over 15mph (~25km/h), 20mph (32km/h) in the USA, and 28mph (45km/h) in Germany. Unwanted attention from the boys in blue could get expensive.
Bear in mind, not all cadence sensors have this feature. You’ll have to ‘manualize’ your riding efforts with the level of pedal assist to suit the riding situation. Let’s say you’re approaching a hill. Ordinarily, you’ll need to downshift to a lower gear to be able to gain more power from the motor, just as you would for any powered vehicle. Your PAS cadence sensor will notice the dropoff in pedaling cadence, and provide less power to get you up the incline. Solution? Get out of your saddle or increase the PAS level to suit.
The biggest disadvantage of this system is the slight delay when you’d like the motor to be active, and the same effect applies when your motor deactivates. In other words, there’s some lag. Eventually, as technology advances in this field, this will become less noticeable.
The cadence sensor’s ring of magnets is mounted on the pedal crank, while the sensor is mounted to the bottom bracket of the bike. If your eBike has a brushless motor, these will act much like a Hall sensor – a device that measures magnetic field differences. Essentially, this technology can be found on the more basic eBike models. While not as intuitive as a torque-based PAS, it’s still very useful – and cheaper than the more advanced system below.
Torque-based PAS sensors
A torque-based PAS on the other hand measures the amount of torque (turning power) being applied to each pedal. In this case the motor starts generating better performance as the sensor relays the data that the rider is applying more torque on the pedals. This almost remains unnoticeable by the rider who just experiences that the power is there when it’s needed. The more force being applied on the pedals, the more useful energy the motor provides.
These sensors are far more accurate than your ordinary cadence sensor. Data is being sent to the controller every millisecond, resulting in a near seamless riding experience with power on demand. A drawback? More expensive than cadence sensors but you get what you pay for here. This is at the cutting edge of eBike technology. There are manufacturers out there that offer a combination of these sensors, a cadence sensor and a speed sensor – this is the pinnacle of the eBike riding experience. As close as bicycling AI as there is in the market.
A final thought, much will depend on what you want out of an eBike. Do you want it for recreation, rehabilitation, fitness, commuting to work, reducing your carbon footprint, going off-road, or even racing? There’s an eBike out there for any of these and more. The world’s your oyster…