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  1. #25
    Community Moderator ger21's Avatar
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    Default Re: RPM on steppers & StepServos

    Use a 2:1 belt drive to run the motor at 600rpm.

    Gerry

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

    Quote Originally Posted by imitheo View Post
    The CG is not in the equation, you relate the average force with the change of momentum that the machine is suffering when deaccelerating to the arm of the force on the CG of the gantry. I THINK this is the way to see if the structure it's going to stay in place.
    It really depends on how the gantry is supported on the rails. The twisting moment may or may not have effect on the overall system.

    I need 1200 RPM because my ballscrew has 10mm lead, and i need 12m/min.
    A 1:2 ratio would put the motor at 600 RPM at 12m/min. With a 35 Kg gantry even a 1:3 ratio would work, thus further reducing the motor RPM. I have found that running stepper motor slower is better, and you can still maintain machine resolution. Just for fun, look at your calculations again using lower motor speeds.

    EDIT: Gerry you beat me to it



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    Default Re: RPM on steppers & StepServos

    What kind of competition is this? High school, college, university? What kind of machine is this? A router? What kind of spindle will you have on it? What are the other parameters you will be tested on?

    Quote Originally Posted by imitheo View Post
    The only thing they state it, is that it needs to pass through the sensors with 12m/min and the machine will have a 75mm to accelerate it to that speed.
    so 12m / min = 472 IPM. This is just a rapid speed? No cutting required at this speed? Acceleration is what limits speed (keeping ballscrew lead and motor performance constant). There are a few types of control software that have a separate acceleration input for rapids. Flashcut, for example. Mach 3 does not, meaning that the same acceleration you use for your rapids is what you have for your feeds. An acceleration of 0.035G will get you to 500 IPM in 65mm. This value is very low, meaning I can't see your machine actually cutting shapes fast with it. That's where the test should focus.

    Your Z axis also needs to hit 12m / min?

    You really need to find torque vs speed graph for the motors! Ask the motor manufacturer if it's not online. This is where you need to start. Also, you need to use the right amp driver and right voltage power supply. Post that info, along with the outer diameter of the ballscrews you're using, the lead you already said was 10mm, the lengths of your screws, the weights of your moving parts, ie: entire gantry, (includes everything including z carriage and z up and down part), Z carriage (includes z up and down part), Z up and down part. Basically all the weights that each screw will move. Also see if you can find the rotor inertia for the motors. I can throw it in my spreadsheet and see what it says. We can compare math.

    A 2:1 belt reduction system should work, but with the low accelerations required, you probably don't need it. Still, you need to do the math. Also, you need to be careful about using higher reductions and planetary gears if you want good acceleration performance. The motor needs to accelerate faster than the ballscrew by a factor equal to the gear ratio when you use reduction. It doesn't sound like fast acceleration is really your goal though.



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    Default Re: RPM on steppers & StepServos

    I found this article online:

    Improving High-Speed Performance of Hybrid Stepper Motors

    Of course you'd need to find a baseline graph for the motors you want to use.

    On a bit of a side note, I realize that you can buy an 8 wire motor and wire it in series or parallel, but has anyone ever taken a 4 wire motor and opened it up and been able to change it to a parallel configuration? Assuming of course, that it was wired in series to begin with.

    I'm guessing that those stepper motors that have feedback encoders and go to the faster RPMs are already wired in parallel even if they only have four wires coming out of the motor?



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    Default Re: RPM on steppers & StepServos

    Quote Originally Posted by imitheo View Post
    The CG is not in the equation, you relate the average force with the change of momentum that the machine is suffering when deaccelerating to the arm of the force on the CG of the gantry. I THINK this is the way to see if the structure it's going to stay in place.
    No, the CG is not part of the speed, but acceleration/deceleration possibilities are worse with high CG and since you can't lose steps or use infinite acceleration and also not running in vacuum, CG is a very important factor. CG doesn't matter for a moving table but the gigher the moving gantry is the more problems you will experience. Just like a low sports car is more efficient in acceleration than another with the same engine, tyres and mass if that other one is considerable higher. Anyone who ever transported a large object on their car roof knows this. The top speed may be the same in the end but it will take much longer to accelerate (not only because of drag) and decelerate, and also the whole journey becomes more unstable, turns insecure (must be taken slower) and so on than if the same car had the same mass placed in the boot and the passenger compartment with lower CG. That's why I am saying "in theory".

    If you have a limited acceleration/deceleration distance, even though in your case that 70mm is HUGE, you must of course try to keep the CG low. One way of doing it is that if you add some extra weight at the bottom, where the ball nut is. It will increase the mass but will move the CG down. Just an idea you might want to try when you encounter speed problems.

    Quote Originally Posted by imitheo View Post
    I need 1200 RPM because my ballscrew has 10mm lead, and i need 12m/min.
    Like I said, with my 1605 and NEMA23 I can get that speed with my moving table machine. So if the CG does not matter, only the mass, then with the 10mm pitch you have you should get twice as much, which of course at least I don't believe in at all, but if you are so sure about that CG doesn't matter then you should not worry at all. 12m/min should be an easy match...

    One thing I don't remember was mentioned is the motion controller and the software you are planning on using. I think those two play an important role as well. I don't think you can get that high speed with parallel port use, but I can be wrong about this as well...

    Using a belt reduces the needed rpm and that in turn reduces the number of steps needed for the speed, and may reduce the need of quality electronics and software as well.



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    Default Re: RPM on steppers & StepServos

    [QUOTE=A_Camera;2060422
    Like I said, with my 1605 and NEMA23 I can get that speed with my moving table machine. [/QUOTE]

    That's 2400 RPM. Fast for a stepper motor. Please forgive my curiosity, but what kind of Nema 23 are you using, how heavy is your table and what are your acceleration settings if I may ask?



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    Default Re: RPM on steppers & StepServos

    Quote Originally Posted by NIC 77 View Post
    That's 2400 RPM. Fast for a stepper motor. Please forgive my curiosity, but what kind of Nema 23 are you using, how heavy is your table and what are your acceleration settings if I may ask?
    https://adapting-camera.blogspot.se/...nt-status.html

    Sorry, I was wrong. 10m/min is my maximum, but even that is more than 1200rpm and if I can get that speed with my 1605s then he should easily be able to get 12m/min with the 10mm pitch screws he is using, especially since some of you claim that moving gantry or moving table makes no difference. My table is 17.5kg without the two vices and the large 10mm aluminium plate plus the PCB fixture I have on permanently, so total table weight, when in use, is about 30kg. His gantry is 35kg, so again, very similar to my table in terms of weight. Specifications for my machine are in the above link. Z weight without stepper and spindle. On my blog there are many other details about my machine and the different stages of building/upgrading. I also have many YT videos.

    https://adapting-camera.blogspot.com
    https://www.youtube.com/channel/UC_vrAWOz5YGX6_e3qtXg3YA


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    Default Re: RPM on steppers & StepServos

    Quote Originally Posted by A_Camera View Post
    Sorry, I was wrong. 10m/min is my maximum, but even that is more than 1200rpm and if I can get that speed with my 1605s then he should easily be able to get 12m/min with the 10mm pitch screws he is using.
    So you could get 10m/min with about 0.1G acceleration using only one motor and 5mm lead ballscrews. That's impressive.

    Are you using the jss-motor 57HM56-3004??

    Changzhou Jinsanshi Mechatronics Co. Ltd.

    I couldn't find a torque vs speed graph for it. 0.9 deg/step instead of 1.8. How is that wired inside? Parallel?

    If we could find a torque vs speed chart for it, the OP could determine it's use for 10mm lead. Perhaps that would solve his problem right there. If that's what you're using?



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    Default Re: RPM on steppers & StepServos

    Quote Originally Posted by NIC 77 View Post
    I found this article online:

    Improving High-Speed Performance of Hybrid Stepper Motors

    Of course you'd need to find a baseline graph for the motors you want to use.

    On a bit of a side note, I realize that you can buy an 8 wire motor and wire it in series or parallel, but has anyone ever taken a 4 wire motor and opened it up and been able to change it to a parallel configuration? Assuming of course, that it was wired in series to begin with.

    I'm guessing that those stepper motors that have feedback encoders and go to the faster RPMs are already wired in parallel even if they only have four wires coming out of the motor?
    That's a really nice article, thanks a lot for it. I knew that increasing voltage would make the motor run faster, but it's good to see graphics and stuff.

    If you have a limited acceleration/deceleration distance, even though in your case that 70mm is HUGE, you must of course try to keep the CG low. One way of doing it is that if you add some extra weight at the bottom, where the ball nut is. It will increase the mass but will move the CG down. Just an idea you might want to try when you encounter speed problems.
    Yes i was calculating the momentum the structure would suffer when deaccelerating or accelerating and it came to me that this 70mm is VERY HUGE. So i am not worrying about my machine base right now. Maybe the vibrations, but i'll be a Ø6 endmill so no heavy milling will be done.

    Quote Originally Posted by NIC 77 View Post
    So you could get 10m/min with about 0.1G acceleration using only one motor and 5mm lead ballscrews. That's impressive.


    Are you using the jss-motor 57HM56-3004??


    Changzhou Jinsanshi Mechatronics Co. Ltd.


    I couldn't find a torque vs speed graph for it. 0.9 deg/step instead of 1.8. How is that wired inside? Parallel?


    If we could find a torque vs speed chart for it, the OP could determine it's use for 10mm lead. Perhaps that would solve his problem right there. If that's what you're using?
    Yes, pretty impressive, i'm starting to feel really confident about my motors and my design. In fact i would like to point that there is a big difference in
    table and gantry design, just like A_camera stated, the CG of the gantry will be really high, so any stops and starts will cause a moment with the arm of the gantry CG.
    The table has a really low CG, so the moment is almost nothing compared to the gantry moment. I am well aware of that, but i'll still go for my gantry design because it will be small.

    And another factor that goes for the gantry is: I'll be using my machine surrounding to make an enclosure. In this competition, we have 12 hours to make the machine, BUT as 12 hours is little time, we can take the structure mounted, but other stuff, like electronics, enclosures and a custom ATC UNIT is demanded to be made there, machined i mean. I'll be personally handling the lathe and the milling center(DISCOVERY 760).



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    Default Re: RPM on steppers & StepServos

    Have anyone ever look at the TBI MOTION ballscrew designing PDF ?

    TBI MOTION Ballscrew

    I used this design guide to know the Torque i would need to drive my gantry. If anyone could take a look with for me to be more confident about these calculations.

    To get the cutting force on my endmill i used this KENNAMETAL calculator:

    KENNAMETAL Calc

    To see the maximum cutting force my end mill could hold, i got the milling parameters for the endmill i am using from kennametal and then inserted in the calculator.

    So with the maximum tangential force i maxed my parameters using my spindle power. Finally i got 90N as my cutting force.

    Anyone could take a look at these ?



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    Default Re: RPM on steppers & StepServos

    Quote Originally Posted by NIC 77 View Post
    So you could get 10m/min with about 0.1G acceleration using only one motor and 5mm lead ballscrews. That's impressive.

    Are you using the jss-motor 57HM56-3004??

    Changzhou Jinsanshi Mechatronics Co. Ltd.

    I couldn't find a torque vs speed graph for it. 0.9 deg/step instead of 1.8. How is that wired inside? Parallel?

    If we could find a torque vs speed chart for it, the OP could determine it's use for 10mm lead. Perhaps that would solve his problem right there. If that's what you're using?
    My motors are bought four years ago and I don't think you can buy those today. They are called 57BYGH633 and sold by Wantai Motors. I have no idea about any other data than what's stated by the documentation.

    Here is a link I found.

    https://adapting-camera.blogspot.com
    https://www.youtube.com/channel/UC_vrAWOz5YGX6_e3qtXg3YA


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    Default Re: RPM on steppers & StepServos

    Quote Originally Posted by A_Camera View Post
    My motors are bought four years ago and I don't think you can buy those today. They are called 57BYGH633 and sold by Wantai Motors. I have no idea about any other data than what's stated by the documentation.

    Here is a link I found.
    Thanks for the info. Some of those torque graphs are almost flat! Not usually what you see with a stepper motor. I'd like to see if there is a Nema 34 motor that is almost flat up to 1300 RPM at about 3.5 Nm. Yes, I could use a servo, but it would be easier to find a flatish type stepper for my own purposes at this point seeing as I already have Gecko drives, power cables, breakout board, etc, for stepper motors.



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