what kind of step motor do i need for this situation?

mahmoudz

Hello.
I want to build a 3d printer with 50501cm (aluminium) BED,
and I realized that at least these dimensions will weigh about 7kg.

Now i have 2 qestions.
1- can 2 step motors 4kg/cm move verticaly this plate along the Z axis without any problem? other parts ( flexible coupling, Lead Screw 8mm).
is this 2 step motor good for this situation?

2- can 1 step motors 4kg/cm move horizantly this plate along the Y axis without any problem? other parts ( GT2 timing belt and pulley 6mm)
is this step motor good for this situation?

Can you please tell me the way to do these calculations for z and y and x axix)?
thanks alot. (please explaining this to me in simple language becuase I did a lot of research And I still do not understand this).

deckingman

@mahmoudz The force required is mass multiplied by the acceleration. Your choice of 8mm lead screws is a bad one IMO because when power is removed (I e. The machine is switched off), then the screws will autorotate and the bed will drop due to the steep helix angle of 8mm lead screws. As for lifting the bed, those screws will give you an effective gearing of about 25:1 but that's not the whole story as there is friction to take into account. My suggestion would be to use 2mm lead screws which gives you an effective gearing of 100:1. This means that you could lift the bed with one quarter of the torque required for an 8mm lead screw, and the bed will stay in position when power is removed. You'll need to do the maths to calculate how fast your motor can accelerate the bed.
As for moving it in the Y direction, the same equation applies (force=massxacceration). So you first need to decide what acceration you want, then calculate the force required. After that, you can use the Duet documentation which will take you to a calculator for choosing steppers. I'm on my phone right now so can't supply links.

mahmoudz

@deckingman said in what kind of step motor do i need for this situation?:

2mm lead screws

thanks.
2mm lead screws is the Threaded rod with 2 start rod?
if we want to use 1mm lead screw (For more accuracy), We have to increase the diameter of the rod? If yes, how much? or we have to
Or we should increase the number of axles so that the load can be distributed?

and could you please tell me more about effective gearing 25:1 abd 100:1 that you mentioned?

And please send me the relevant link for the calculation later.

Thanks alot

deckingman

@mahmoudz Take a look at this video that I made about 2 years ago. It will explain everything you need to know about lead screws https://www.youtube.com/watch?v=o_0xdrKUYVU.

The effective gearing is derived from the fact that we converting angular movement to linear movement. So for example a 1.8 degree motor will have 200 full steps per revolution. With an 8mm lead screw, the linear movement will be 8mm. 200/8 = 25.

Here is one link to choosing stepper motors https://docs.duet3d.com/en/User_manual/Connecting_hardware/Motors_choosing

I can't off hand find the calculator for torque but I've uploaded the spread sheet to my google drive. You can find it here.

https://drive.google.com/file/d/1KkYBxoOVfrH8YVWT_r5rgT8KrbULmAIa/view?usp=sharing

mahmoudz

@deckingman
Thanks alot

mrehorstdmd

@mahmoudz My printer's 3.5 kg bed has a belt lifted Z axis that is about 695 mm long. I used a NEMA-23 stepper with a 30:1 worm gear reducer to lift it. The same drive would easily lift 7 kg. Belts don't flex or bend and cause Z artifacts, and the bed doesn't move when Z motor power is cut off- no additional braking is needed. The motor is operated at about 1/2 rated current and driven directly by the driver on a Duet2 board, so there is no special configuration required- just enter steps per mm and it's ready to work.

This is the motor/worm gear I used.

Belts do stretch a very little, but my testing has found that it isn't enough to affect print quality with "normal" print layer thickness.

deckingman

@mahmoudz For completeness sake, my bed is 400mm x 400mm x 12mm thick with 6mm of glass on top and 12mm of insulation underneath. Adding a bit more for the weight of the frame on which it all sits, I'd estimate the weight to be close to your 7Kgs. To lift this, I use a single Nema 23 driving three 8mm dia 2mm lead screws via a continuous belt.

mahmoudz

@mrehorstdmd
Thank you for your guidance. Thanks alot

mahmoudz

@deckingman
Thanks. Sorry for asking so many questions. Because I do not have much experience in this field
could you please tell me more about this:

1- 2 stepper motor 17 nema, cant lift the 7kg bed? What is the maximum weight these 2 stepper motor 17 nema can lift?

2- I watched your video about lead screw carefully on YouTube. In some parts of the video, you said that one of the things to fix backlash in 3D printers is to increase the weight of the machine to use the law of gravity to remove the backlash. You also said in the 16th minute for backlash" that the guide should be nice and free" what is the guide? You mean a rod that is not threaded and is placed next to the lead screw?

3- And experimentally, how much should the weight of the printer with 50x50 bed?

4- and if we use Nema 23, It is still possible to use this board or this board must be changed completely (mega2560 with ramps1.4)?
and power of the printer also have to chage?

I am doing a lot of research, I met you in this forum. Can I have your email so that I can ask you if I have any questions?

Thanks again

deckingman

@mahmoudz

I did have a single Nema 17 on my axis, rated at about 45Ncm IIRC. That single motor would lift the bed using 2mm leads screws but only at about 450mm\minute. Speed is not normally a factor for the Z axis but if I print something that's 750mm tall, it would take over a minute and a half to re-home the printer. But two of those Nema 17s would work. In the event, I changed to a single Nema 23 rated at much higher torque allowing me to raise the bed that 750mm in far less time.
You misunderstand. Gravity will take care of the backlash on the Z axis - the same flanks of the thread will always be in contact regardless of the direction of rotation. Your 7Kgs will be more than sufficient.
I don't understand your question. Concentrate on making the printer rigid and accept that the weight will be what every it comes out at. Weight is not a factor unless you plan on picking it up and carrying it some distance.
Nema 17s and Nema 23s are just different physical sizes. Nema 17s are 42mm x 42mm, Nema 23s are 57mmx57mm. The important thing is how much current your chosen stepper motor will draw. You haven't said which board you are going to use so I can't answer your question. The Duet 3 6HC mainboard can handle motors up to 6.3Amps peak which will be more than sufficient for your needs. IIRC, the drivers on the Duet 2 series could handle a maximum of 2.4Amps peak. Other Duet boards have different drivers so you'll have to check the specs.
There are many knowledgeable people on these forums. I don't usually have much spare time to answer questions - today was an exception. So if you have further questions, post them on these forums - you'll get answers faster than if you were to send me an email. Remember to start a new thread for a new topic and provide as much information as possible. In the meantime - read everything! The documentation is a good place to start. https://docs.duet3d.com/

mahmoudz

@deckingman
Thank you very much for your help.