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5 Things You Should Know About the E-bike Motor

Posted by Yoel Farzan on
5 Things You Should Know About the E-bike Motor

Have you caught the e-bike fever yet? The vehicle that has become cool all of a sudden and is available in some very economical options? Here is something to reassure you, you are not the only one catching up with the excitement over these bikes. Just like yourself, a lot of people are scrambling with the specs and features they need to check out. It gets all the more confusing with the sea of information available about e-bikes. The e-bike motor is one such feature that boggles the minds of aspiring bikers. How do you identify which one suits you more? And what is a power rating? What difference does it make if you ride a 500 e-bike motor or a 750W? Thankfully, we have successfully narrowed down all things e-bike motors to five key points. Read along to find an easily digestible beginner guide on e-bike motors.

1. How it works

Naturally, this is the first question that pops into your mind when thinking of an e-bike motor. It does what it is supposed to do – translating electrical energy into mechanical. Owing to efficiency and longevity, the Brush Less Direct Current Motor (BLDC) is the standard for e-bikes. If you inspect BLDC, you will find a couple of wires wound around a series of circular poles forming what is known as a stator. Inside or around the stator, you have circular permanent magnets which make the rotor. As the rider uses the motor controller to draw current from the battery into the wires, it turns the stator electromagnetic. The permanent magnets on the rotor are attracted and repelled by the electromagnets, spurring a spinning action. For a mid-drive motor, the stator attaches to a shaft. The shaft spins, generating torque and offering pedal assistance via the chainring attached to the stator. But for front and rear hub motors shaft behaves like an axle and cannot spin as a result. Instead of that, it is the rotor that spins, making the motor spin along. As a result, it generates torque propelling the front or rear wheel.

2. Power ratings 

It is one of the most marketed metrics when it comes to e-bikes. The actual power output depends on how much load you have added to the e-bike and the maximum current a controller allows under such circumstances. A power rating only informs you about the power you get for a given time. And it only adds to the confusion that there is no standard duration to determine the peak or rate power. For example, a motor may peak at 750 watts for just a few seconds, only to drop back to 500 watts of continuous power. Getting the watt-hours generated by the battery instead of the e-bike motor power rating is a better measure of what you’ll get. To find the numeric, multiply the e-bike battery voltage with the amperes for a motor controller. With some research, you may collect information (from vendors, ace cyclists) about the percent efficiency to arrive at a more realistic number. So, if you have a 48 V e-bike battery and a 15 amperes controller, the ideal power should be 720 watts. Assuming a 75% efficiency (loss of efficiency could be due to several reasons), you can get 540 watts. The final wattage we got is very close to the 500 watts power rating marketing for various e-bikes. Doing your homework will help you identify what you are getting and what it’s worth.

3. Its interaction with the bike

Motors are not the only component helping the bike spin faster. An e-bike motor works with components like controllers and batteries to deliver the entire experience. Riders pedal the bikes to draw current from the batteries into the motor. Controllers regulate the power flowing from the battery to the motor during cycling. Rider inputs such as the force exerted on the pedals and controller use determine the amount of current flowing towards the motor. Thus, giving you an e-assistance or power on an e-bike. E-bikes with a pedal-assist have a speed sensor or torque sensor in place to regulate e-assistance. A speed sensor controls power by measuring the pedaling cadence, whereas a torque sensor regulates by checking the torque generated by the rider. Riders can also enjoy throttle-assisted e-bikes, which offer power assistance independent of the pedaling. However, due to this feature, e-bikes are sometimes categorized as a moped or even scooters.  And are subject to similar regulations as conventional motorized vehicles. Before finalizing your new e-bike, it is beneficial to review applicable local regulatory requirements and decide accordingly.

4.Types of motors

Mid drive motors

These motors are present between the e-bike cranks and offer assistance via the chainring, complementing your pedaling within the bike’s chain drive. The gear protection system ensures the motor spins at rider-friendly speed. 

  Pros Cons
Mid-drive Motors Easy to lift and carry, thanks to the balanced weight distribution. More expensive
  The lower center of gravity makes it ideal for off-road riding. Chain drive has a shorter life span. 
Front Hub Motors Relatively cheaper (commonly found on folding/touring bikes). Balance issues because of the heavier front wheel.
  It does not wear down the chain. The motor pulls forward instead of push (can feel strange).
Rear Hub Motors Less likely to wear down the chain. Balance issues may arise.
  It pushes you forward (feels more natural). It could be tricky to steer.

Front hub motors

A front hub e-bike motor goes on the front wheel within a hub. In this scenario, the shaft is the rear axle, and the e-bike motor revolves around it to propel the bike forward.  

Rear hub motors

You can find the e-bike motor on the rear hub in this configuration. It also uses axle as shaft and spins as riders pedal the e-bike. Both front and rear hub e-bike motors have a larger diameter in direct-drive e-bikes to gain better torque output and eventual ease in riding.

 

 

5. Geared motors

 

 

A common issue with all three types of direct drive motors is that they are heavy since they need a larger size to produce the torque to spin the wheel faster at lower RPMs (rounds per minute). Geared motors solve the size problem while still maintaining the bike’s efficiency. A geared motor spins much faster. Its shaft connects to a series of plenary gears attached to the hub. So, as the motor spins faster than a direct drive motor, the gears ensure that the hub spins at a slower rate, generating more torque and a balanced speed. Geared hub motors have a smaller diameter than direct-drive ones.  But have a more wide hub to accommodate the plenary gears. Another plus point to these motors is the freewheel wheel mechanism, making cycling it just as when not switched to the power mode.

 

 

Final word

 E-bike motors draw current from the e-bike batteries. These motors have high revolutions per minute; e-bike manufacturers compensate with more size or geared motor configuration to generate high torque and a balanced speed. You often see motor power ratings as a measure of the e-bike’s capacity. It is wise to look for battery voltage and controller amperes instead, do the math and conduct a little research about the product efficiency from the manufacturer. There are three types of e-bike motors depending on their position on the bike. Mid-drive e-bikes give you the best experience but tend to be on the pricier side. Direct drive hub bikes can put off the balance, but turning to geared motors in either configuration improves the situation. Sometimes you can get a simulated power rating. Go for it if you get a chance to gain a better idea about the vehicle. And finally, it is best to do a test drive and gauge the kind of ride you get before making the final call.  

 

 

Source: https://hd-ebike.com/blogs/5-things-you-should-know-about-the-e-bike-motor/

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