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    Default Need someone that has a bigger brain then me to help me calculate gearing.

    Hi all .,

    Ok ., i have absolutly NO math part in my brain when it comes to calculations like this..

    But im having ideas building in my brain and i worry im totally wrong with my thinking , and probably i am.

    Stepper motors... Faster they go , lower the torque

    BUT , and here it comes BUT , if one would gear up his steppers ? what happends with torque ?

    if im running my steppers on 100 procent speed , i might be getting 5 procent torque , if i then run my steppers on 10 procent speed and getting maybe 90 procent of my torque and gear up lets say 1:9 with a gear on my stepper and a gear on my ballscrew.. Will i still have torque ???

    Can someone try and explain how all this works in laymans term so i might have a chance of understanding it , and just maybe also learn a bit about it ..

    Thanks in advance

    Kristjan

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    Default Re: Need someone that has a bigger brain then me to help me calculate gearing.

    To keep it simple:
    Bigger pulley on motor say 50mm, smaller on screw say 25mm (2:1) will half speed and double torque.
    Bigger on screw 50mm, smaller on motor 25mm (1:2) will double speed and half torque.

    So using same 50mm pulley in the example:
    50/25 changes by factor of 2
    50/10 would change by factor of 5
    50/5 would change by factor of 10


    I don't know if the ratio's I put in are opposite way around but you get the idea.



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    Community Moderator Al_The_Man's Avatar
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    Default Re: Need someone that has a bigger brain then me to help me calculate gearing.

    Quote Originally Posted by Kristjan1505 View Post
    Hi all .,


    Stepper motors... Faster they go , lower the torque

    BUT , and here it comes BUT , if one would gear up his steppers ? what happends with torque ?

    if im running my steppers on 100 procent speed , i might be getting 5 procent torque , if i then run my steppers on 10 procent speed and getting maybe 90 procent of my torque and gear up lets say 1:9 with a gear on my stepper and a gear on my ballscrew.. Will i still have torque ???

    Can someone try and explain how all this works in laymans term so i might have a chance of understanding it , and just maybe also learn a bit about it ..

    Thanks in advance

    Kristjan
    Simply put.
    They only lose torque due to the increased inductive reactance as rpm increases, this results in a reduction in current, so the secret is, is to use a method in order to maintain the plate current as close as possible.
    Originally this was done with a simple series resistor, but modern drives use a voltage much higher that the plate voltage of the motor, and use this voltage, in order to Maintain the required current throughout the RPM range.
    Steppers should ONLY be ran at the manuf. plate current and no other.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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    Community Moderator Jim Dawson's Avatar
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    Default Re: Need someone that has a bigger brain then me to help me calculate gearing.

    Look at it this way

    Motor pulley = Ball screw pulley = 1:1 ratio. Torque and RPM at the ball screw are equal to the motor.

    Motor pulley = 10, ball screw pulley = 20, 2:1 ratio, torque = 2X, RPM = 0.5X, ball screw turns slower than the motor, torque is doubled

    Motor pulley = 20, ball screw pulley = 10, 1:2 ratio, torque = 0.5X, RPM = 2X, ball screw turns faster than the motor, torque is halved.

    In most applications motor is direct coupled to the ball screw, 1:1. In some applications the motor could be geared down, to a maximum of about 3:1. I don't think I have seen any CNC machine with a motor/ball screw gear ratio greater than 3:1.

    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: Need someone that has a bigger brain then me to help me calculate gearing.

    ok closer to the gearing at least .,

    But im still not really understanding if i would be gaining from my gearing..

    1000 rpm = 100 procent torque
    10000 rpm = 1 procent torque

    im running my steppers at 8000 rpm and getting 5 procent of my torque
    if i run my stepper at 1000 rpm , and gear up 1:8 will i still only be getting my 5 procent torque ?

    Sorry for pea brain





    Quote Originally Posted by Jim Dawson View Post
    Look at it this way

    Motor pulley = Ball screw pulley = 1:1 ratio. Torque and RPM at the ball screw are equal to the motor.

    Motor pulley = 10, ball screw pulley = 20, 2:1 ratio, torque = 2X, RPM = 0.5X, ball screw turns slower than the motor, torque is doubled

    Motor pulley = 20, ball screw pulley = 10, 1:2 ratio, torque = 0.5X, RPM = 2X, ball screw turns faster than the motor, torque is halved.

    In most applications motor is direct coupled to the ball screw, 1:1. In some applications the motor could be geared down, to a maximum of about 3:1. I don't think I have seen any CNC machine with a motor/ball screw gear ratio greater than 3:1.




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    Default Re: Need someone that has a bigger brain then me to help me calculate gearing.

    Let's use some realistic numbers. In general the upper practical RPM limit for a stepper motor is around 1200 RPM, but maybe there are some steppers that will run a bit faster. The stepper torque drops off rapidly as the RPM increases. Steppers produce maximum torque at 0 RPM (holding torque), and very little torque at maximum RPM.

    8000 RPM by a stepper is not possible. At 1000 RPM, most steppers would produce very little torque. So if you had it geared up 1:8, you would have almost no torque available to run what ever you want to run.

    If you really need to run something at 8000 RPM, then a stepper motor is not the correct motor to use.

    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: Need someone that has a bigger brain then me to help me calculate gearing.

    No no ., im aware that numbers are not realistic at all and was more thinking the numbers as theoretical numbers.. it was more the concept of it , so in real life numbers lets say im using the 1000 rpm and getting my 1 procent , and 10rpm was my 100 procent , if then the gearing was 1.10 i would be getting my 1000 rpm , but would i still be getting only 1 procent torque , or would my torque increase a bit ?



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    Default Re: Need someone that has a bigger brain then me to help me calculate gearing.

    Sounds like the motor drive is not suitable or capable??
    Torque increases proportionatly with gearing.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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    Community Moderator Jim Dawson's Avatar
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    Default Re: Need someone that has a bigger brain then me to help me calculate gearing.

    OK, maybe to explain it another way

    Motor RPM = 1000
    Motor torque = 10 (the units make no difference)

    at 1:1 ratio the motor and driven shaft RPM and torque are equal

    at 10:1 ratio Driven shaft = 100 RPM, torque = 100

    at 1:10 ratio, Driven shaft = 10,000 RPM and torque = 1

    Jim Dawson
    Sandy, Oregon, USA


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Need someone that has a bigger brain then me to help me calculate gearing.

Need someone that has a bigger brain then me to help me calculate gearing.