Nema 23 Questions

deckingman

@timvukman From an electrical/electronics point of view, stepper motors aren't in my field of expertise but from a mechanical point of view, I can make some observations which might help.

Firstly Nema 23 and Nema 17 refer to the physical dimensions of the stepper motor and do not necessarily mean that torque will be higher. As a general rule, a larger motor will produce more torque but one can have high torque Nema17s and low torque Nema 23s. Generally longer motors have more torque than shorter ones, so a long Nema 17 might have more torque than a short Nema 23.

What you really need to do is calculate the torque requirement to produce the force required to accelerate the mass at the desired speed. Or conversely, if you know the torque of the chosen motor, calculate the maximum acceleration that would be obtainable. (It takes very little force to maintain a mass at a constant speed, but a hell of a lot of force to accelerate up to that speed).

It's been a long time since I last did the calcs for my printer but this'll give you some idea of the process. I used a few fudge factors and I think there are probably better calculators out there.

Holding torque=59N.cm at rated current. Take 85% for running at 85% current = 50.15N.cm Take 71% to allow loss due to micro-stepping = 35.61N.cm. Reduce by 59% for torque loss due to speed = 17.8N.cm. Divide by pulley diameter in cm to get force in Newtons so 17.8/0.6 = 29.7 Newtons.

Now take carriage mass. In my case it's really heavy - much heavier than your X, possibly heavier than your Y but substitute your own mass. In my case it was 1.67Kgs. Force = Mass*Acceleration so Acceleration is Force/Mass so 29.7/1.67 = 17.77 m/sec^2 or in 3D printer terms 17,667.71 mm/sec^2. But take 10% of that to allow for drop in torque due to micro-stepping so say 1,776.77 mm/sec^2.

There are a lot of fudge factors in the above but you get the idea. So in simple terms, a single Nema 17 with rated holding torque of 59N/cm could accelerate a mass of 1.67Kgs at 1,776 mm/sec^2. In practical terms I can say that yes, this is possible as I've tested it.

How does this translate to speed? Speed is sqrt(2accelerationaxis length/2). Assuming you have a modest axis length of 200mm, then if we plug the above numbers into that formula we get 596mm/sec maximum attainable speed.

In reality, print speed is governed by how fast you can melt filament and you are unlikely to be able to lay down filaments at much over 100mm/sec unless you use very small nozzle diameter and or/ small layer heights and/or (as I do) multiple melt chambers. So that example of a single Nema 17 driving a mass of 1.7kgs would potentially allow you to attain speeds 6 times higher that you could reasonable print at. Although a high non-print speed is desirable. But also, you need to have a very rigid frame to be able to use high accelerations, especially if the mass is high too.

Sorry for all the maths and a long rambling post but without knowing the masses involved, the desired acceleration, and the available torque, there is no way to say whether a particular motor would do the job (but at a guess, I'd say you would be fine).

wilriker

@deckingman Ian, if I only would have known you a year ago. I was looking for a calculation similar to yours and for the life of me was not able to find it. It was for a totally different purpose (a motorized barn-door tracking mount for astrophotography) but having known what you described would have saved me from buying a totally overpowered stepper.

Mind, if I turn this into an online calculator?

deckingman

@wilriker said in Nema 23 Questions:

@deckingman Ian, if I only would have known you a year ago. I was looking for a calculation similar to yours and for the life of me was not able to find it. It was for a totally different purpose (a motorized barn-door tracking mount for astrophotography) but having known what you described would have saved me from buying a totally overpowered stepper.

Mind, if I turn this into an online calculator?

I think it's been done. At least I'm sure that someone did a better calculator taking other things into account. I'll email you the spread sheet that I have though.

Bear in mind that I'm just an old guy who cuts and screws bits of wood

wilriker

@deckingman said in Nema 23 Questions:

I think it's been done. At least I'm sure that someone did a better calculator taking other things into account.

Probably, but till this date I was not able to find something that is not either too simple or totally over-complicated with friction coefficients etc.

I'll email you the spread sheet that I have though.

Thanks, looking forward to it.

Bear in mind that I'm just an old guy who cuts and screws bits of wood

You always make yourself smaller than you are.

deckingman

@wilriker said in Nema 23 Questions:

You always make yourself smaller than you are.

No seriously, I am old and I do cut and screw bits of wood together (admittedly this is career number 9 or something)

Anyway, spread sent via email.

wilriker

@deckingman said in Nema 23 Questions:

No seriously, I am old and I do cut and screw bits of wood together (admittedly this is career number 9 or something)

I know. But now I have to start nitpicking because originally you said you are just an old guy who... And yet your are one of the most helpful members of this community (at least to me) and I already learned quite some interesting and important stuff from you.

Now enough of the flattering. And thread hijacking - we should not let this become a habit.

TimVukman

@deckingman
Thank you for laying out the calculations. That is very helpful information. I will keep it on a piece of paper near my printer since I seem to always be changing / trying something different.

Really appreciated!!
Tim

TimVukman

@wilriker
I don't consider this thread hijacking. I found it entertaining. May be I could get a copy of that spreadsheet? I shall even ask nicely.

May I please have a copy of that wonderful spreadsheet?

Thanks.
Tim

wilriker

@timvukman I am currently reading the rather old thread the spreadsheet is based upon. Ian told me that there are some more refinements to find.

Once I gather all the information I will create a small online calculator from it. This will maybe be end of this week but rather likely start of next week. If you cannot wait that long (I could totally understand ) I will ask (hereby) @deckingman for permission to upload it as a Google Spreadsheet in the mean time.

TimVukman

I got to thinking after that discussion that the mechanical composition of the axis must have a great deal to do with the final results.

My X axis came from China. It's a complete system which has a nema 17 coupled to a lead screw. The lead screw goes through a brass threaded bearing that one would normally find on a Z axis gantry. There is nothing for anti-backlash and it chatters like crazy while printing. The play is noticable in the final printed object.

My Y has two parallel linear bearing rails, but very small linear bearings. A plate mounts to those, but only in opposite corners. I have a brass threaded bearing that the threaded rod goes through and that rod is coupled to a Nema 23. The brass bearing is held to the edge of the plate with multiple windings of wire which is quite secure but not very impressive to look at.

I really want a system that is smooth and precise. I am constantly looking at various linear motion systems, but they are expensive and I want to be sure it's the final answer before I fork out the cash.

Obviously, from the discussions in this thread there are important considerations / calculations that should be done before anything gets ordered.

I've spent quite a bit on various systems, but I could have saved quite a bit if I knew enough to buy the ideal solution up front.

Maybe I should have made a new thread for this, but I would appreciate input.

I'm also looking at CNC hardware which seems to use larger rod sizes and I don't know if that would make any difference.

Thanks
Tim

TimVukman

@wilriker
As you will see by my latest addition to this discussion, I am not in a hurry. I've hit the point where I want to stop trying to hack something together and would prefer to do it properly.
Thanks
Tim

wilriker

@timvukman said in Nema 23 Questions:

I've hit the point where I want to stop trying to hack something together and would prefer to do it properly.

I have yet to hit that point.

Anyway, I'll be posting the link to the calculator here once it is finished.

Re: your printer mechanics: I have not yet seen or heard of a (Cartesian) printer that drives anything but the Z axis with leadscrews. I have no experience on doing so but I have a feeling that this adds tons of inertia and backlash. The latter could be counteracted with anti-backlash nuts but that will add friction which again slows everything down.

My printer runs on smooth rods with Igus bearings and GT2 belts for X and Y and I am totally happy with that and backlash can easily controlled but adjusting belt tension without slowing down anything considerably.

TimVukman

Yes, I am familiar with the belt setup. My printer started as a Tevo Tarantula which was belt driven. I think I am still using two pieces of the original frame for my spool holder. Everything else has been replaced.

I did quite a bit of research before adopting the threaded rods. Everything I read about belt driven systems seemed to emphasize things like stretched belts and skipping teeth under load. I suspect now, that what I read was produced by the threaded rod companies.

I have been thinking about returning to belts. It seems like a good exercise in simplicity. Your comments on inertia and backlash are supported by experience.

Take a look at these. I find them hard to resist :). Anything used in medical ought to be smooth and accurate, I would think.

https://www.thomsonlinear.com/downloads/actuators/Stepper_Motor_Linear_Actuators_bren.pdf?utm_term=Download the new brochure %2526gt%3B&utm_campaign=How can you reduce design and assembly times&utm_content=email&utm_source=Act-On+Software&utm_medium=email
regards,
Tim

deckingman

@timvukman said in Nema 23 Questions:

Yes, I am familiar with the belt setup. My printer started as a Tevo Tarantula which was belt driven. I think I am still using two pieces of the original frame for my spool holder. Everything else has been replaced.

I did quite a bit of research before adopting the threaded rods. Everything I read about belt driven systems seemed to emphasize things like stretched belts and skipping teeth under load. I suspect now, that what I read was produced by the threaded rod companies.

I have been thinking about returning to belts. It seems like a good exercise in simplicity. Your comments on inertia and backlash are supported by experience.

Take a look at these. I find them hard to resist :). Anything used in medical ought to be smooth and accurate, I would think.

https://www.thomsonlinear.com/downloads/actuators/Stepper_Motor_Linear_Actuators_bren.pdf?utm_term=Download the new brochure %2526gt%3B&utm_campaign=How can you reduce design and assembly times&utm_content=email&utm_source=Act-On+Software&utm_medium=email
regards,
Tim

The trouble with forums is that they are populated by armchair engineers who read something (usually posted by someone else) which may be relevant to a 30 tonne metal shaping machine, and assume that it must me relevant to a small 3D printer for no other reason than it also has an axis that has linear motion.

Ditch the screws. Use timing belts. Timing belts don't stretch because their function is not to stretch and that is what they are designed for (the exception being imitations that come from parts of the world where people tend to be small and have funny shaped eyes).

I didn't realise that you were trying to use screws for X and Y motion. Forget that spread sheet and those calculations - they are not relevant to screw driven axes.

I haven't read the specs but the actuators you linked to will likely by too slow and have too limited travel for application in a 3D printer. Being "medical" they'll likely cost a fortune too (but I guess they'd be hygienic and won't contain nuts).

wilriker

@deckingman said in Nema 23 Questions:

(but I guess they'd be hygienic and won't contain nuts).

I'd rather say they either drive you nuts or have to ability to cure you from that state.

deckingman

@wilriker I should have said that being "medical" they'll likely cost an arm and leg but you need to be a native English speaker to understand that.

wilriker

@deckingman Now I feel confused (in my national identity) because I understand it but cannot find the German equivalent in my head right now.

TimVukman

Hi:

I haven't left, I was just busy rebuilding the printer again.

So, to the important part first.
ein Arm und ein Bein according to google translate, which does not understand context or nuances:) For all I know, the saying may not even be used in German. I find other languages challenging since they seem to have a whole different word for everything!:)

I removed my Y axis. It was never as solid as I wanted it to be. I build another box out of extruded 20 x 40 V-Slot and put a linear slide bearing on each one, I have a carriage plate spanning the two rails. On the carriage plate, I have two (one at each end - front and back) bronze threaded bearings that the lead screw goes through.

The hot bed is mounted to two rails mounted to the carriage plate. It is a very solid assembly with excellent movement. I went back to the Nema 17 motor and changed the config.g setting back to what they were before the Nema 23.

I printed an almost perfect configuration cube. (the corners aren't perfectly square and I know I have some play in the X axis.

Having said and done all that, I think that I am going to replace the threaded rod with belts. Physics clearly implies that belts would be smoother and provide less resistance to motion. So, I have seen pulley ends with 16 teeth, 20 teeth, etc. Is the number of teeth important? What about belt size?

This just never ends I was printing something last night, and I received a heater fault message. I now get a constant 2000 degree reading on the hot end heater. Shouldn't be too hard to figure out.
Thanks
Tim

deckingman

@timvukman said in Nema 23 Questions:

So, I have seen pulley ends with 16 teeth, 20 teeth, etc. Is the number of teeth important? What about belt size?

This just never ends I was printing something last night, and I received a heater fault message. I now get a constant 2000 degree reading on the hot end heater. Shouldn't be too hard to figure out.
Thanks
Tim

Pulley diameter doesn't matter too much IMO. I prefer 20 teeth as the bend radius is a but less and they seem to be more commonly available. If you do the maths, 20 tooth on a gt2 belt is 40mm per revolution so you get 5 full steps per mm (one full step is 0.2mm). With a 16 tooth pulley it's 32mm per revolution so one full step is 0.16mm which is a bit of an odd number. But in either case, for resolutions less than 0.2mm, you have to rely on micro-stepping for accuracy so not much to choose between them.

6mm wide belt is fine. I use it to throw 3Kgs around at highish speed, so for your printer it'll be perfectly OK.

2,000 degree C usually means something is open circuit (e.g. bad crimp or broken wire)

TimVukman

Thanks
I shall start understanding what I have in my collection of pulleys.

I replaced the entire extruder with a new E3d V6 that I had just received. This one did not have a plastic tube in so it jammed up on me. I now have the tube all the way in and it is extruding. It's making a mess which I would normally say is over extruding, but it is using the same bowden as the previous one which was laying down nice lines.

More investigation required, I guess, but not heater error anymore.
Tim