How to calculate torque output of a BLDC motor...
Hi I'm looking to understand how I might calculate the maximum torque of a bldc motor and also how to understand how to calculate gear ratios - based on the motors default specs, with a view to increasing torque (presumably at the cost of speed and efficiency)
I don't mind being directed toward relevant online tutorials and tools and I'm not really expecting anyone to simply educate me here in the forum.
Below is a bullet point list of things that have been buzzing round my head in relation to the device I'd like to design and fabricate. Please note, I'm a complete novice (and also a maths dunce) but I'm willing to learn and to put in effort. The project is in no way intended for a commercial application although I do feel like being a little tight lipped about the specifics , because I hate being beaten to the punch.
List of thoughts bouncing around my stupid non-engineer brain:
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| Thoughts on BLDC Motor |
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* How (if at all) does the number of coils on the stator effect speed, torque and efficiency?
* How does the number of windings per coil effect the speed torque and efficiency of the motor?
* How does the gauge of the wire effect the above? Obviously heavier gauge = lower resistance and also
places a limit on the number of windings. How are those variables proportional to one another?
* How (if at all) does the supplied voltage effect the speed and torque of the motor?
* How do you calculate the torque value of a motor in relation to things like voltage and other variables
mentioned above? What are the key variables that define the attribute of torque output?
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| Application of the motor |
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* The motor will be small.
* The motor will be used like a winch or pulley.
* The motor needs to be able to pull a constant load of 45 kg which, I believe works out as 441.299251288751 Newtons of torque, or 0.441299 kilonewtons.
* Ideally I do not wish to supply the motor with more than 9 volts of power (is power the correct term?)
* I expect to have to gear the motor down. I will achieve the requisite gear ratio using a planetary system because it is the most compact gear system and the end product needs to be small.
* What are the necessary attributes of the motor that I need to know in order to calculate its maximum torque?
What other attributes are important to know about the motor?
With a given set of values that pertain to the motor; how would I use those values to calculate a gear ratio that would pull 45 kg?
How would I juggle those numbers with a view to plugging in different values in order to find a happy compromise between winding speed and torque. I presume that drum size would be an important factor.
1 Answer
The biggest problem you have to overcome is your complete lack of understanding of the basic mechanics that you need to develop to come up with the answers you want. The first step is to properly understand the fundamental building blocks that mechanical design is based upon. You need to know what mass is, what a force is, Newton's Laws of motion being a good place to start as all of the mechanical theory an engineer learns and the practical application of the work of Newton is where you need to start.
If you had a standard New Zealand high school science and physics education you would at least know where to start. I would assume a British education would be similar to the NZ one, so you either stayed away from the Maths - Science option at school, or were asleep in the back of the class for these subjects.
From the gibberish you have posted as regards to your knowledge of forces, power, torque rotational dynamics and other fundamental mechanical knowledge that are required to work out the machines you are interested in, means you need to start down this path, at the absolute beginning. Start off with some high school level physics / mechanics texts, then move on to first year engineering / technician texts after that. see if you can develop a real understanding of this material, then go from there.
