Starting to design out my build, looking for critique

[Chrono]

If by12m/s your meaning 12 meters per second then your massively off with your settings. 12 Meters per Min is more realistic figure.

To be honest that spread sheet is load of rubbish and spits out unrealistic figures. Real world is much different due to the many variables that affect machine performance.

Ah yes, indeed it is 12m/min, don't know how I have read that wrong every single time...

I have been using the spreadsheet to dimension all my motors so far. Is there a better way to do this, or will it all just come together in the final build? I am guessing there is no real way to account for all the variables the steppers will be influenced by when it comes to it, but I guess what I am asking is: Is it still a good idea to run the motors you can find through the spreadsheet to find the "best one" you can still drive?

[JAZZCNC]

Ah yes, indeed it is 12m/min, don't know how I have read that wrong every single time...

I have been using the spreadsheet to dimension all my motors so far. Is there a better way to do this, or will it all just come together in the final build? I am guessing there is no real way to account for all the variables the steppers will be influenced by when it comes to it, but I guess what I am asking is: Is it still a good idea to run the motors you can find through the spreadsheet to find the "best one" you can still drive?

Lots of things come into play, not all motors are equal for instance and same size motor can have ridicuously high inductance compared to another and the spread sheet doesn't and cannot really account for these variables.
Combine this with all the other variables and it's very much trial and error in some ways.

For instance I've helped folks troubleshoot machines with motors that would lift empire state building yet they stall and run slow because they wrongly sized components like ballscrews, gearboxs ratios etc or they did such poor job of building and allignment the machine is crippled.

The best advice I can give is to look around for similar size machine built with similar materials/components and copy what works.

Thru experience I can tell you that Single 4Nm nema23 with inductance around 2-3Mh wired in parallel running 4 to 4.5A with 68Vdc on 80Vdc Digital drives connected to 16mm Dia10mm pitch ballscrew with a Good motion controller (not parallel port) will easily and reliably reach 12M/min moving 40-50Kg.

For longer than 1200mm 20mm 10mm pitch screws you'll need to use nema 34 or use method like I suggested using larger pitch with ratio.
Same for dual screws you'll need 2 x Nema 23 upto 20mm Dia, Single 4nm Nema 23 won't drive 2 screws, even with ratio.

If you go to nema 34 then for better speeds you'll need more volts.

[MartinS]

Thru experience I can tell you that Single 4Nm nema23 with inductance around 2-3Mh wired in parallel running 4 to 4.5A with 68Vdc on 80Vdc Digital drives connected to 16mm Dia10mm pitch ballscrew with a Good motion controller (not parallel port) will easily and reliably reach 12M/min moving 40-50Kg

Hi Chrono,

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?

and

I mostly tend to fit Closed loop hybrid steppers these days and many of them can be driven with AC or DC.

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

Thanks,
Martin

[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?