Large Delta printer build - advice and suggestions welcome

[Trakyan]

@Reefsider, I'll just offer some small things to think about. Regarding 2 motors vs 1, you've worked with a few industrial machines by the sounds of it, have you ever seen 2 motors driving one belt? I'd have to guess not, and there is a reason for that. Ask any I3 user and they'll tell you their 2 Z motors can get out of sync, only imagine those two steppers were tied together, they'd be fighting each other. That and they'll be fighting each other all the time since their steps and microsteps wont be exactly the same. Just use one bigger motor. I can't think of any application where motors are coupled together like that.As for cable drives, they've been done before, and I'm a fan of them. That being said, the reason to use them is generally because they are cheap, or because they can be routed in 3 dimensions which isn't really useful in a delta where you need one straight back and forth loop. String drives also have a few issues to deal with, specifically pulley walk (where the string winds up one side of the pulley as it turns in one direction, and then walks the other way when the pulley turns the other way). This isn't an issue in steering systems where the pulley doesn't rotate too many times, but on a 3d printer the drive pulley makes a lot of revolutions from one extreme of the axis to the other which means the string will walk a lot. The other is triangulation error, strings are often routed (or end up due to pulley walk) at a slight diagonal which can cause minor cosine error. The triangulation error is mostly at the extremes of travel where the carriage gets close to the pulley (which you wont use much on a delta), but even then isn't huge. The final issue which I think is overstated is slipping, cables don't have teeth like belts and can slip. That being said with a couple of wraps around a drive pulley you'll find the stepper will skip steps before the cable slips on the pulley.Also, I'd second CA's suggestion of using wheels. A delta that's moving fast, especially in a zig-zag type of way like for infill will have a fair bit of vibration. Linear rails are pretty shoddy at vibration damping, it's one of the reasons subtractive machines tend to use box or V ways instead.Have a look at nicholas seward's builds, they're fairly exotic as far as their mechanics go, but he tackles a lot of the issues cable drives can have. I don't think he's eliminated the issues I've mentioned in any of his machines, but focused more on making them so small that they don't matter realistically. There's a few solutions that completely fix the string walk and triangulation issues I could point you to if you decide to go that way.

[AutoWiz]

. Ask any I3 user and they'll tell you their 2 Z motors can get out of sync, only imagine those two steppers were tied together, they'd be fighting each other. That and they'll be fighting each other all the time since their steps and microsteps wont be exactly the same.

Do tell. You do know I 3D printed an entire i3 printer and I did it all right here, right? Well here is that: https://3dprintboard.com/showthread....ted-3D-Printer
And while I have 2 other i3 style printers and one that I converted to 2 z motors I have never once had this 'out of sync' issue you claim. Honestly you sound like a Neanderthal making ape noises. lol @ you. Nobody wires 2 stepper motors together unless they are already using car parts and don't mind setting house fires. The rest of us use 1 stepper driver per stepper motor and we tee off of the input signal to feed the second driver. A good example of this can be seen here: https://www.youtube.com/watch?v=vIChqkEAuto&t= Now go pound some sand. Or sit down and give your mind a rest or w/e.

[Reefsider416]

@Reefsider, I'll just offer some small things to think about. Regarding 2 motors vs 1, you've worked with a few industrial machines by the sounds of it, have you ever seen 2 motors driving one belt?......Also, I'd second CA's suggestion of using wheels. A delta that's moving fast, especially in a zig-zag type of way like for infill will have a fair bit of vibration. Linear rails are pretty shoddy at vibration damping, it's one of the reasons subtractive machines tend to use box or V ways instead......

What made me think 2 motors might be better than one is purely from RC cars and boats. It is quite common to use 2 servos for one control. Stepper motors are basically just fancy servos. Also i have a prusa I3 MK3 and it has 2 z steppers and I would say it works better than my first printer which only had one. I think its probably best to use one larger one but its worth considering. Also, if you use separate drivers i believe you can manually control the very fine initial position with the pot on the driver. I could be wrong though, I am trying to build my first printer now. I guess i should say rebuild because its a Mono Price Select Mini V1 but the firmware crashed so I am trying to install an SKR Mini E3 DIP but having some issues. also upgraded the printer substantially. making a post in a minute about that.

Anyways, I think both are probably fine one set up probably would have better acceleration and one might have slightly better accuracy or something but that's all something I can play around with if I get some time.As for the Cable system it is just a random thought. I am building this printer with GT2 stuff but may play with it later and see what i can come up with. I also saw a hydraulic system on youtube that has crazy accuracy and insane speed lol. I'm sure it's too expensive but fun to think about different ideas and set ups.


With the linear rails; You'r probably right about the vibration dampening. I guess the point is to make the printer so rigid there is little to vibrate. I worked briefly for the Canadian distributor of a well known Japanese CNC/EDM machine company and I have seen some pretty crazy subractive CNC mills, lathes and wire EDM machines and i have never seen one with box extrusions or wheels or V slots. These machines are pretty much solid cast iron. When I went to my first install I was surprised by the size of the crane truck that was needed to get it off the mac truck flat bed. They pretty much all had linear rails of some sort. A lot of ceramic bearings and fancy accordion covers and jackets or shrouds etc but never have I seen wheels or guide rods of any kind or extrusions except for the mounting surface for parts so you can use t-slot clamps to hold parts.

Some of the machines didn't even have bearings on the linear rails. They were simply made to such a fine tolerance they slid perfectly on each other. At that point its almost changed from friction to hydrodynamics because of the layer of machine oil on everything and the fine tolerances. This system is used more on lathes than a moving bed situation but same idea, eliminate slop and make it as rigid as possible.

Most of the drive systems were ball drives except for the really fancy stuff that had linear motors (mag lev tech as i call it) which increased speed and accuracy substantially. Rigidity was the name of the game in CNC. It's why all the machines were as much one piece cast iron as possible. Its the only way they can get the accuracy which was insane. One of the machines advertising pamphlet showed it could engrave over 100 Japanese characters on a grain of rice. Also could drill a square grid of 100 holes in a HB pencil lead, on the rounded side/face. That kind of accuracy requires all the moving parts to have a fitment of unbelievable accuracy, rigidity and absolutely no perceivable play.

I'm not saying that's what a 3d printer needs but I think with any machine, rigidity and the least play is going to yield the best results and allow the fastest speeds while maintaining those results. Its kind of like old domestic cars vs old German cars. German cars were built to a higher tolerance which is why they lasted a lot longer and were generally faster. Now the tolerances are less of an issue with cars, mostly because the CNC machines that make the parts and/or moulds/stamps are more accurate as well.

There are ways of isolating vibrations but you cant fix slop. Just my opinion from my experience, I am not an expert and only dealt with one brand of CNC machine so take it for what its worth.