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I'm going to design an electric bike using a BLDC motor.

According to my knowledge there are two types of BLDC motors: normal BLDC motors and stepper motors.

Can I use a large stepper motor for the ebike?

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  • \$\begingroup\$ What for? Stepper motor are usually employed when high angular position/velocity is required. For an electronic bike your specification probably includes torque only, you can then go for a much cheaper and easyer to pilot standard BL motor. \$\endgroup\$ Commented Sep 12, 2015 at 17:02

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Well, yes, a stepper could be used. But why?

A BLDC (brushless DC) motor often has an on-board controller or driver for energizing each of the coils in the correct sequence and at the correct time. A DC voltage is applied, and it just works.

BLDC motors are most often optimized for medium-to-high-speed and medium-to-low torque applications, such as fans and servos. They do not have precise positioning capability; or in other words, zero repeatability (ignoring closed-loop servos.)

In contrast, a Stepper motor is similar to a BLDC motor, except without the on-board controller or driver. So you are required to provide the energizing current to specific coils, at the correct rate, and for the correct duration. A typical driver is something like this instructable, utilizing the ULN2003A driver chip, which makes design easier.

Stepper motors are most often optimized for medium-to-low-speed, and medium-to-high torque applications, such as mechanical positioners, paper feeders, CNC machining, robotics, etc. They DO have precise positioning capability (because you control each pulse which turns the stator.) Each pulse turns the stator a set number of degrees, based on the design of the motor. Common "step angles" range from 1/8th through 1/128th revolution. So very precise control of shaft rotation is possible. This is why they are commonly used for precision positioning applications, and if utilized in a feedback loop, have 100% repeatability. Their torque decreases as the rotation speed increases, however. So it would be more work to use a stepper motor, with little to no gain.

Here are some starting calculation examples to size the motor appropriately.

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  • \$\begingroup\$ @ rdtsc Thanks rdtsc. this is a perfect answer for my problem. \$\endgroup\$ Commented Sep 12, 2015 at 17:30
  • \$\begingroup\$ Step angles of 1/200 revolution are very common, and with half-step controllers will produce 1/400 revolution steps. \$\endgroup\$ Commented Sep 12, 2015 at 23:57
  • \$\begingroup\$ "Micro-stepping" or "PWM-stepping" can produce even more steps than this. But often more steps is a moot point, as final gearing commonly negates the necessity for finer resolution. Also, for finer-step motors, the maximum torque and speed decrease dramatically. So while they may function perfectly for aligning a very slow-moving scanning-electron-microscope target, they can't drive say, any practical robot servo. So finer resolution is possible... for a price. This is why lower-step-angle steppers (4,8,16 step/rev) are often chosen for higher-speed applications. (CNC, robotics, etc.) \$\endgroup\$
    – rdtsc
    Commented Sep 13, 2015 at 16:49

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