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.
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.
Best Answer
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.
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.