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  1. #11
    Technician
    Join Date
    Jul 2015
    Location
    Durban, South Africa
    Posts
    68
    Add ZorAxe on Thingiverse
    Quote Originally Posted by DBFIU View Post
    ...Also, are you saying these motors have a a sort of dyno graph? One NEMA 23 can make more or less torque at 2 amps vs another NEMA 23?...
    In a way yes there should be a graph that will show the different torque and what the amount of current drawn is at the particular torque figure. If I remember correctly, "The torque generated a the motor is proportional to the amount of current flowing through the motor." Basically what I meant is find 23's that will give you the most for their values:

    Lets make an example:
    You have 2 NEMA 23's.
    -----------
    Motor A has 4.0Nm holding torque at 6A
    Motor B has 1.6Nm holding torque at 2A
    -----------
    On paper it seems as Motor A is more powerful (and it is) but if your driver can only supply 2A then it's not possible to run the motor at full torque.
    If I'm correct in saying torque is proportional to current then Motor A will only push out 1.33Nm torque at 2A, making it less powerful then Motor B.

    I stand to be corrected in the above statement, and please do correct me if I'm wrong. It's just something I came across when I was choosing motors for my CNC engraver. So keep those calculations in mind when looking for motors. Your drivers limited to 2A and that plays a big part.

  2. #12
    Banned
    Join Date
    Jan 2015
    Posts
    306
    Quote Originally Posted by ZorAxe View Post
    In a way yes there should be a graph that will show the different torque and what the amount of current drawn is at the particular torque figure. If I remember correctly, "The torque generated a the motor is proportional to the amount of current flowing through the motor." Basically what I meant is find 23's that will give you the most for their values:

    Lets make an example:
    You have 2 NEMA 23's.
    -----------
    Motor A has 4.0Nm holding torque at 6A
    Motor B has 1.6Nm holding torque at 2A
    -----------
    On paper it seems as Motor A is more powerful (and it is) but if your driver can only supply 2A then it's not possible to run the motor at full torque.
    If I'm correct in saying torque is proportional to current then Motor A will only push out 1.33Nm torque at 2A, making it less powerful then Motor B.

    I stand to be corrected in the above statement, and please do correct me if I'm wrong. It's just something I came across when I was choosing motors for my CNC engraver. So keep those calculations in mind when looking for motors. Your drivers limited to 2A and that plays a big part.
    That would be assuming the current/torque relationship is linear, and if you interpolated it linearly then yes I see what you mean. But what if the curve is not straight?

    Maybe I am overthinking this part of the plan..

    Either way thank you for the input, it is always appreciated.

  3. #13
    Senior Engineer
    Join Date
    Jun 2014
    Location
    Burnley, UK
    Posts
    1,662
    He is correct. One of the reasons for that is if you make a motor that has max say of 2 amps then it does not get as hot and expand as much as a motor that is designed to take say 4 amps. Because of that the 4 amp motor has bigger clearances between the rotor and the stator and magnetic fields in air cost a lot in terms of power

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