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  1. #41
    I think it's more clear to me now.

    Requirements
    Speed: standard 0-2000mm/min max 3000mm/min
    RPM needed:
    5mm lead; standard 0-400RPM, max 600RPM
    10mm lead; standard 0-200RPM, max 300RPM

    A stepper motor seems to lose it torque from 300-500RPM
    A standard servo motor has full torque up to 3000RPM. However to utilize the whole range I would need a 10:1 or a 5:1 reduction.

    5mm lead will put me over the speed where the stepper starts to loose torque but it will also give me twice the force of a 10mm lead. I'm not sure i'm going to machine over 2000mm/min but for rapids I need a higher speed.

    The weight of the X and Y cart is 30Kg. The Z cart is 20Kg
    Cutting force; max 150N

    After reading more on servos the torque advantages are clear. If my machine was bigger it would be obvious to use them, with the size om my machine there is not so much of a difference.

  2. #42
    You could always use more powerful Stepper motors to negate the loss of torque at higher rpm. Also you could simply run your machine with higher rapids using servos so less of a gear reduction is required. 10mm pitch 10m/min rapids and a 3:1 reduction doesn't sound too bad! Ball screws have a maximum rotation speed so make sure you're not going to be over rotating them. 1,000 rpm is a pretty conservative speed but just be careful when it comes to spinning long ball screws at higher rpm.

    If you'll be happy running at 3m/min then Open Loop Steppers will be a good choice. Rpm and microstepping both change the available torque so it'll be best to work out what torque will be required and choose the motor based on your calculations.

    Cheers,

    Fenza

  3. #43
    Quote Originally Posted by PotatoMill View Post
    Requirements
    Speed: standard 0-2000mm/min max 3000mm/min
    RPM needed:
    5mm lead; standard 0-400RPM, max 600RPM
    10mm lead; standard 0-200RPM, max 300RPM

    A stepper motor seems to lose it torque from 300-500RPM
    A standard servo motor has full torque up to 3000RPM. However to utilize the whole range I would need a 10:1 or a 5:1 reduction.
    If you buy a not Chinese stepper, probably it is higher, like the price :) But yes, you should calculate up to 500rpm.
    With 5mm lead from 2:1 to 3:1 usually enough with servos. On 2.5:1 ratio I can get up 6000mm/s no-load speed on 3000rpm. But some motors could do 4000rpm.

  4. #44
    Quote Originally Posted by Fenza View Post
    You could always use more powerful Stepper motors to negate the loss of torque at higher rpm. Also you could simply run your machine with higher rapids using servos so less of a gear reduction is required. 10mm pitch 10m/min rapids and a 3:1 reduction doesn't sound too bad! Ball screws have a maximum rotation speed so make sure you're not going to be over rotating them. 1,000 rpm is a pretty conservative speed but just be careful when it comes to spinning long ball screws at higher rpm.

    If you'll be happy running at 3m/min then Open Loop Steppers will be a good choice. Rpm and microstepping both change the available torque so it'll be best to work out what torque will be required and choose the motor based on your calculations.

    Cheers,

    Fenza
    Why not closed loop?

  5. #45
    Quote Originally Posted by PotatoMill View Post
    Why not closed loop?
    Personally I'm not a fan of closed loop steppers... Open loop steppers are cheap and Servos are great performers, closed loop steppers are neither...

    I think it is possible for you to achieve your desired level of performance using the cheaper open loop steppers. 3Nm stepper should probably be around about right directly coupled to a 5mm ball screw.

    Servos you'd be looking at 100-200W I believe.

    Hope this helps!

    Fenza

  6. #46
    Quote Originally Posted by Fenza View Post
    Personally I'm not a fan of closed loop steppers... Open loop steppers are cheap and Servos are great performers, closed loop steppers are neither...
    Fenza
    A bigger steppers is a good idea. You can get enough torque in a no-load operation. Just you will get higher inertia as well.

  7. #47
    I have heard open loop steppers is not good for point to point 3D toolpaths. They loose step easy and you cant push them very well.

  8. #48
    Quote Originally Posted by PotatoMill View Post
    I have heard open loop steppers is not good for point to point 3D toolpaths. They loose step easy and you cant push them very well.
    Closed loop steppers are a solution looking for a problem, correctly designed open loop systems don't lose steps, if that can happen on a machine then it's badly configured or broken.
    Closing the loop doesn't make a bad machine good, using the correct motors & screws and running it within it's limits does.
    If you will not be swayed by logic or experience simply pick the idea you
    like best, but ask yourself why you sought advice in the first place and,
    for a simple life, perhaps consider not doing so in future

  9. The Following User Says Thank You to magicniner For This Useful Post:


  10. #49
    Quote Originally Posted by magicniner View Post
    Closed loop steppers are a solution looking for a problem, correctly designed open loop systems don't lose steps, if that can happen on a machine then it's badly configured or broken.
    Closing the loop doesn't make a bad machine good, using the correct motors & screws and running it within it's limits does.
    While this is true generally, closing the loop with servos definitely makes machine faster. I also am not fan of the closed loop steppers price wise.

    But if the machine will be machining Metal i dont see why at all there is a discussion for sth else than servos and closed loop. Given the price of aluminum material that will be machined and eventually a mistake made.
    project 1 , 2,Dust Shoe ...

  11. #50
    Quote Originally Posted by magicniner View Post
    Closed loop steppers are a solution looking for a problem, correctly designed open loop systems don't lose steps, if that can happen on a machine then it's badly configured or broken.
    Closing the loop doesn't make a bad machine good, using the correct motors & screws and running it within it's limits does.
    Well said.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

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