Choosing the right motor.


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    Default Choosing the right motor.

    First hi. That is my first post here and i wanted to say hello. And second I hope I post this in the right category and it is not answered to often.

    So my question I am about to build a cnc mostly to 3d carve foam like EPS but also thin plywood. With the help of others I created the drwaing you see below. It will be made of steel and the X-Axis will have a travel of 3.6m and y-Axis 1.2m. X-Axis will be rack pinion and y and z ballscrew. All axis run on linear guides. So far so good. Most of the travel will happen on the x-axis. So it would be great if x-axis could run fast. So many things have clarified for me already. Ahh and maybe I have to add that the ballscrew on the y-axis have diameter of 22mm. Only because I can get it for free (if you say I should better choose a thinner one I am open for this)

    Now all that said I am about to choose my motors for this build. I tend to use stepper motors simply because of the cheap price.
    Which motor would you recommend (type and size). And should it have an encoder attached? I also would be happy to get other recommendations.

    Thats the link to my Autodesk drawing if you like to take a look. I also added a pdf drawing in the end.
    https://autode.sk/2v0Hk9T

    thanks a lot

    Felix

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    Default Re: Choosing the right motor.

    That's a rather odd-looking machine concept. Is there a particular reason for those proportions? If you have a special part you're making, and this machine is only designed to make that one thing, then it might make sense, otherwise you might find it limiting when you want to do other projects.

    You might want to beef up that long gantry beam in the vertical direction, since it will tend to sag in the middle otherwise.

    Actually building the machine first, and then shopping for motors, is generally a good idea. Things tend to change as a build progresses, and you don't want to be stuck with a control system that's not appropriate for the new design. The extra time will allow you to do more research into the various alternatives, and mull over things like torque curves, inductance, and power requirements.

    Andrew Werby
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    Default Re: Choosing the right motor.

    Quote Originally Posted by awerby View Post
    That's a rather odd-looking machine concept. Is there a particular reason for those proportions? If you have a special part you're making, and this machine is only designed to make that one thing, then it might make sense, otherwise you might find it limiting when you want to do other projects.

    You might want to beef up that long gantry beam in the vertical direction, since it will tend to sag in the middle otherwise.

    Actually building the machine first, and then shopping for motors, is generally a good idea. Things tend to change as a build progresses, and you don't want to be stuck with a control system that's not appropriate for the new design. The extra time will allow you to do more research into the various alternatives, and mull over things like torque curves, inductance, and power requirements.
    Yes it is for a quite a special purpose. But will have options for a table and Y-Axis travel is 1,2m so it can also be used for some other purposes hopefully. The long x-axis is also my major concern. But I will make it from steel 150x150x 1cm (and not two 80x40 Aluminium beams stacked as I intended before.) So I hope it will be stiff enough.

    Good advice of building first the machine. I will let the motor issue rest for now.



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    Default Re: Choosing the right motor.

    To select the ideal motor, you need to know the following:

    How fast do you want to go?
    How fast do you want to accelerate?
    How much weight are you moving?
    What are the specs of the rack and pinion you are using?


    Are you building your own pinion drives, or using CNC Router Parts drives? If the latter, then use the motors that they sell.

    Gerry

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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: Choosing the right motor.

    Yes I think because all these questions will arise during the build I guess it is better to postpone the motor question. But some i could answer Y-Axis will be slow but it has to push a lot of weight. 22mm ballscrew and the X-axis beam. The rack pinion I will build myself. I was told to take a 5:1 gearbox. X-Axis will be the one which runs the most and should be quick. On the other hand it "only" has to move the Router which and Z-Axis which I try to make from Aluminium and as light as possible.



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    Default Re: Choosing the right motor.

    What kind of machine has one axis moving slower than the other?

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Quote Originally Posted by ger21 View Post
    What kind of machine has one axis moving slower than the other?
    Sorry I am really new to this. But my idea is that because my machine has a long xaxis and relatively small y axis. So it will do one stroke over the xaxis and during this not moving a lot on taxis. So in numbers one stroke xaxis 3500mm, yaxis max 300mm and zaxis 100mm max movemen. The movement will be more or less continuously.so yes to my understanding they will be different in speed



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    Default Re: Choosing the right motor.

    You really don't want one axis to be slower than the other. There wouldn't really be any cost savings in doing so, and it will impact performance.

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: Choosing the right motor.

    Having faster rapids on the longer axis will help a bit, but for cutting, no reason for one to be faster than the other (you'll be limited by the slower one.)
    Do you have access to any simulation software? Or just run it through a deflection formula? That long axis is long. Not sure how well that beam will hold up under its own weight. Just the beam will be around 180 kg, not including the rails, drive stuff or the carriage. A taller profile while keeping the wall thickness the same will have less sag.
    22mm ball screw is fairly thin for over a meter span. Have you done any whip calculations? What's the pitch?
    From what I've heard DIY R&P can be a tough nut to crack. Good low-backlash gearboxes can be pricey. Do you know what diameter pinion you're going to use?



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    Default Re: Choosing the right motor.

    Quote Originally Posted by skrubol View Post
    Having faster rapids on the longer axis will help a bit, but for cutting, no reason for one to be faster than the other (you'll be limited by the slower one.)
    Do you have access to any simulation software? Or just run it through a deflection formula? That long axis is long. Not sure how well that beam will hold up under its own weight. Just the beam will be around 180 kg, not including the rails, drive stuff or the carriage. A taller profile while keeping the wall thickness the same will have less sag.
    22mm ball screw is fairly thin for over a meter span. Have you done any whip calculations? What's the pitch?
    From what I've heard DIY R&P can be a tough nut to crack. Good low-backlash gearboxes can be pricey. Do you know what diameter pinion you're going to use?
    Hey changed my design to a more conventional one. I was convinced by you and several other more experienced then me. Now the y-Axis became the long one 3600mm with hopefully 3300-3400 travel. X-axis travel is shortened to 800mm travel. See the attached image. The motor question is still postponed. But I am convinced now to take 4 same type motors (not sure if Servo or Hybrid). I roughly calculated I want to be able to cut 8m per minute on a foam cut on the Y-axis. Which is the one with the rack pinion. Is that a lot? For the Ballscrew I found a replacement ready made secondhand combo. Also the Z-axis will be a combo. So that i only have to care about the Y-Axis. Sorry no I don't know the width of the Y-axis Rack pinion. any suggestions? A friend of mine is dealing with gearboxes so that I hope to get two cheap ones.

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    Default Re: Choosing the right motor.

    Can't help you with R&P stuff, but on your new layout you should try and make some triangle structures in between the two long rails vertically to make it a truss. That will make it much stronger than the 2 individual beams.



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    Default Re: Choosing the right motor.

    yes I know. it's not finished yet. still collecting ideas. I will do that. I have the top beams on the cnc as 100x100x8. but because I will mill them they will become thinner. All the other beams are 80x80x4, Do you think the sizes are good?



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Choosing the right motor.

Choosing the right motor.