Starting to design out my build, looking for critique

[JAZZCNC]

Dean,

For those of us who are learning and planning, could you expand on the above?

Is this 60BYG401-03 https://cnc4you.co.uk/resources/Step...1-03%204Nm.pdf an example of the stepper categorised above? or if you have another preferred source/model, what is it?

Yes those are good motors which I've used many times. The sheet say's it all really When wired in parallel the Inductance is 3.0mh which is a good value. The lower the inductance the better.

Are those different from the above and do they need different drivers?

Yes and No.
Yes they are still a stepper motor but they have encoders built into them.
No because while they are stepper motors the drives they use are more like Servo drives and designed to read the encoder to track the motors rotation.
Normal stepper drive just recieves pulses and tells the motors to rotate but doesn't actually check or know if actually rotated the commanded distance. So for instance if your axis is binding stiff or very heavy you could lose steps and neither the drives or control software(mach3) know anything about it which leads to inaccurate cuts.

Closed loop drives work differently in that they use the Encoder on the motor to check if it rotated the commanded distance. If it over shot or under shot they correct it's position so returns to commanded position. If they over shoot more than programmed distance they will throw a fault message that can be sent to the control software so can stop the cutting.

While they are Not Full Closed loop, meaning they don't feed the motor position back to controller which still takes it on blind faith that commanded position as been reached. They are a good alternative because they do correct for small positional errors inside the drives and warn the controller if large positional errors occur. Compared Standard stepper drives which have no clue where the motor ended up so can not tell the control software if errors occur. The first you know about it is when the job is finished and wrong or worse machine crashes because it's got lost.!!

So in short yes they are different and need special drives, No they are still stepper motors.
Often you buy the closed loop drives and motors together as a set. Like these.
https://www.ebay.co.uk/itm/CNC-Hybri...IAAOSwjlVcIJIb

https://www.ebay.co.uk/itm/NEW-Leads...UAAOSwqFBbvGxS

Hope that helps.

[MartinS]

Yes, thanks, most helpful.

So in short yes they are different and need special drives, No they are still stepper motors.
Often you buy the closed loop drives and motors together as a set. Like these.
https://www.ebay.co.uk/itm/CNC-Hybri...IAAOSwjlVcIJIb

https://www.ebay.co.uk/itm/NEW-Leads...UAAOSwqFBbvGxS

I guess that we still need a low inductance. I can't see it specified in the links.

[JAZZCNC]

I guess that we still need a low inductance. I can't see it specified in the links.

Yes the same applies but I've yet to find a Closed-loop drive/motor combination that uses high inductance motors and just about every set I've used gives reasonable torque at higher speeds, most reach 1500rpm before torques drops away.

Also, there are closed-loop systems that use 3 phase motors which give much better torque and smooth operation. To be honest I mostly fit 3 phase systems on larger machines.

The only thing you have to watch for with smaller closed-loop systems is that they use low voltage, often 50Vdc drives and they do not tolerate more than 50V and will be damaged if rises above. This means you need to run safe margin, 44 - 45V is recommended. That said they still tend perform very well and better than a standard stepper at same voltage. Think this must be to do with the way the closed loop drives work.!

The bottom line that I've found is that closed-loop systems tend to be slightly stronger at higher feeds and the closed-loop drive ensure the position is maintained.

That said a correctly sized and set up Open-loop stepper system is just as accurate and shouldn't lose position if tuned correctly. Thou Closed-loop systems are coming down in price and the difference in price is now such that closed loop is the wiser choice.

[Chrono]

So, if i got that correctly, I want a stepper that has a low inductance rating and a high current rating, correct?

I plan to use a single NEMA 34 for both X-axis screws(2x 1800mm 2020 screws, around 75kg of mass on the gantry) and a single NEMA 34 for the Y axis as well (1300mm, single 1620 screw, around 25kg of mass to move), with a NEMA 23 for the Z-Axis(single 500mm 1610 screw, 15kg). Taking another look with those qualities in mind, I come up with the following choices:

• X-Axis: ST8918M6708-A
• Y-Axis: ACT 34SSM8460EC
  
• Z-Axis: 60BYG401-03
  

Would these be good choices for my system?