RPM on steppers & StepServos


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Thread: RPM on steppers & StepServos

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    Default RPM on steppers & StepServos

    Hi guys, have anyone tried to run a CNC machine using high RPM on steppers. I wish to run using 1200 RPM, that seems like a lot to me.

    But the deal is, it needs only the 1200 RPM for a really brief period, and only one time! It's a really specific application.

    My concern is, i need to mill a part after this "sprint", BUT i can rehome the CNC machine, so i ask you guys, can i rain hell on the stepper for a brief period and then rehome to regain my home position?

    Will some NEMA 34 hold agaisnt this 1200 RPM?
    Will it lose much steps?
    Can it be done in any software? This "routine"


    A friend of mine told me of some "StepServo", like this: (I don't know how to hide the link)

    https://pt.aliexpress.com/item/Free-...0-05b0c5764ebb

    He says that can be operated at higher speeds without losing too much torque, is this true ? What is this step servo?

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    Registered Biggs427's Avatar
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    Default Re: RPM on steppers & StepServos

    A stepper is a stepper; it will lose torque at higher speed.

    I've seen high rpm on steppers, but only on nema 23, with 40+ volts PS and low inductance steppers. (Less than 2.0mH)

    Why do you need to "over drive" your machine so much?

    What are the specs of your, motor, drive, PS&



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    Default Re: RPM on steppers & StepServos

    It's a competition in my university envolving cnc mills. One of the tests is this, reach 12m/min on each axis.

    But the cost counts on the overall game, so i don't want to go servo, i want to try using a cheaper option, like a step servo or stepper motor.

    I was considering these options: Leadshine ES-M Series - Easy Servo Motors

    We still don't have a motor of our choice.



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    Community Moderator ger21's Avatar
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    Default Re: RPM on steppers & StepServos

    Do you need to move a lot of weight?

    A smaller, low inductance Nema 34 motor (±3Nm) running at higher voltage should easily achieve 1200rpm. Leadshine AM882's from Ebay are inexpensive, and will work.
    But, it really depends on how much weight you need to move.

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    Default Re: RPM on steppers & StepServos

    I think the gantry will weight max 35kg, or 30kg.



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    Default Re: RPM on steppers & StepServos

    All servo motors aren't super expensive. You can get a regular dual-shaft brushed DC motor and mount an optical encoder on the back shaft, transforming it into a servo. You can drive it with a G320 drive from Geckodrives using the same step-direction pulses as a stepper. If you really need those short bursts of speed, that might be the way to go.

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    Default Re: RPM on steppers & StepServos

    I would prefer to go with an "off-the-shelf" solution



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    Default Re: RPM on steppers & StepServos

    Quote Originally Posted by imitheo View Post
    It's a competition in my university envolving cnc mills. One of the tests is this, reach 12m/min on each axis.
    Is that 12m/min on each or at the same time? Because that's quite different. Also, how fast the axis moves also depends on if it is direct drive, or using some sort of gearing or belt, ball screws or trapezoidal, and of course the screw pitch. I am using direct driven 1605 ball screws and NEMA 23 steppers. The drivers are driven with 43VDC and the maximum speed I can get is about 12m/min but that's the absolute maximum, so I run slower. Speed also depends on the rigidity of your machine. Mine is a moving table type, fixed gantry is easier to make and is considerably more rigid and can get the speed up then a moving gantry type, which is often limited because of the mass which is needed to be moved around and also the flexing and vibrations you get from the moving gantry type. So, if speed is important then a fixed gantry, moving table wins.

    But also, speed is just one factor and maximum speed is not that important unless you can also get high enough acceleration AND milling speed and of course, accuracy and repeatability comes before any speed requirement. So if it is a university competition, they should also look at all those factors. It is totally pointless to drive fast if you are missing steps or can't repeat the moves.

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    Default Re: RPM on steppers & StepServos

    I am aware of this "pointless" issue, but the score goes to the team that reaches 12m/min. Everybody is probably going to servo it, but i'm using a Ø6 endmill, i'll not be able to use the 12m/min to mill of course, then my machine will actually mill it much slower.
    That's the catch i'm trying to do, get the score by raining hell on a stepper, get a reduced cost and then feeding my rapid and G1 much slower(Because using it slower will garantee my work piece precision and repeatability).

    My design is a moving gantry, that weights 30kg.

    One axis per test, not the three all together.



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    Default Re: RPM on steppers & StepServos

    Just to put things in perspective, I routinely move my 300KG table at 15M/min, at 0.13G acceleration, about 570 RPM, with a 1280 oz/in NEMA 34 stepper. Geared 1.5:1 with a 40mm lead ball screw. Feeding the drive with a 80V power supply.



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    Default Re: RPM on steppers & StepServos

    Jim, do you have any pictures of your machine ?



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    Gold Member Jim Dawson's Avatar
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    Default Re: RPM on steppers & StepServos

    Quote Originally Posted by imitheo View Post
    Jim, do you have any pictures of your machine ?
    Here is the best one I have. This is a moving table machine. I could supply more pictures if it would be helpful to you.
    http://www.cnczone.com/forums/attach...d=364926&stc=1

    Attached Thumbnails Attached Thumbnails RPM on steppers & StepServos-img_0048-jpg  


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