1
\$\begingroup\$

Firstly, I want to make a BLDC motor WITH hall effect sensors to maximize the torque. I have a heavy mountain bike and I love to make long trips with it. But in my city, there are REALLY steep mountains which can be challenging with extra luggage. I want to make a compact BLDC motor in the rear or front hub which can make a little boost on the hills. I need torque, not speed. I'll use it just for boost, I won't convert my bike into a motorcycle.

So, I designed a BLDC motor that isn't so accurate for maximum torque but gives an idea for the design. I will start from inside to outside. First, we have a shaft in the center which is linked with 8 neodymium magnets around it. Then, we have the case which has the 3 phase coils and hall effect sensors in it (probably I will use 3 hall effect sensors). Then, we have the electronics which are linked with coils. And last, we have the lithium-ion batteries linked around the case. I'll add one of the lithium-ion batteries for better understanding. The volt and amp can be changed; it is for better understanding.

Lithium-Ion Battery Example

Side view design for the hub motor

The magnets are not moving; coils, electronics, and batteries are spinning with the wheel.

I hope the photos will be helpful. I will also make it waterproof and dustproof so it can't have the cold wind in it. So I taught that I can fill it with engine oil. The outside will be aluminum so it will be cold I think.

Now, let's come to my questions. As I said, I'm 10th grade and don't know so much about electrical engineering.

My first question is: When BLDC motors off, do they affect my normal riding, like convert my power into electric or just make so much friction because this is a motor? I mean, when I don't pedal, does bicycle stops faster than before?

Second question: I don't know so much about how to install hall effect sensors. I googled it and find some info. But if you can tell a little bit again, it will help so much. And I know I should use ESC but I don't know how to install it, like which cables in my motor will go where?

Third question: What upgrades can I make for high torque, low speed?

Fourth question: How thick wires should I use like 250watt motor and how to wind them?

Very thanks for reading this and I hope you understand what I meant and you can answer my questions. Sorry for my bad English.

\$\endgroup\$
4
  • \$\begingroup\$ How do you plan to drive the motor? You need to first manage to vary the electromagnetic flux across each coil in a particular order so that you generate a rotating field which causes rotation of the rotor. And for that you need a driver like this: researchgate.net/profile/M_Doss/publication/312070861/figure/… \$\endgroup\$
    – GNZ
    Commented Mar 25, 2020 at 10:22
  • \$\begingroup\$ @GNZ He asked re using an ESC - which is what you are commenting on. \$\endgroup\$
    – Russell McMahon ♦
    Commented Mar 25, 2020 at 12:30
  • 1
    \$\begingroup\$ @Gamer This is a hard task starting from the beginning. You would have a much easier time using either a commercial motor made for ebike use or repurposing a motor intended for something else. | \$\endgroup\$
    – Russell McMahon ♦
    Commented Mar 25, 2020 at 12:32
  • \$\begingroup\$ You have to remove heat from the coils and making it pass through the batteries to escape isn't a good idea. Also, with the inertia of the spinning batteries, coils, and iron, it is going to be hard on the motor and ESC to accelerate and decelerate (and take longer doing so). Filling with oil makes it heavier again and adds drag. You seem to be running away with complexity here. This also sounds really expensive. Take a step back and think about how you are actually going to do all this, and not just the end result you want. \$\endgroup\$
    – DKNguyen
    Commented Mar 25, 2020 at 13:43

1 Answer 1

Reset to default
1
\$\begingroup\$

When BLDC motors off, do they affect my normal riding...

Yes. The attraction between the magnets and the steel core fo the windings will cause "reluctance torque" that will be like a small amount of braking. If the coils are connected together through the ESC, there can be generator action that could be used to charge the batteries, but that would add to the pedaling torque unless the ESC is arranged to do that only while coasting downhill.

how to install hall effect sensors...

What you have drawn is the right general idea. However two pulses per revolution will probably not be satisfactory.

About the ESC

An ESC that rotates is not a good idea. It will be difficult to provide reliable operator interface, difficult to mechanically balance the wheel, and difficult to design a mounting arrangement.

How to design the motor

Motor design is a complex task. Every aspect must be calculated. The torque is proportional to the magnetic flux. Flux is proportional to the area of the air gap, the space between the rotor and the stator. The length of the air gap is also important, The length is the small distance through the air between the rotor and stator. Then you have the strength of the magnets, the number of poles, the number of turns of wire, the voltage, the current, the ESC design etc. The thickness of the wire is determined by the current, the insulation temperature rating and the ability to cool the coils.

Overall assessment

As commented by @Russell McMahon, what you have described is very difficult to do. It would be much easier to purchase the major components and use them to convert a bicycle. A conversion can be a challenging project. You should do that and other less challenging projects before attempting a project of the scale that you have described.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.