Proof of Concept: The CoffeeMaker
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Wow. Does no one have any fun with 3D printing/printers, everything has to be really technical?
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@coffee I bet they would love the deltesian.
https://bornity.com/deltesian-hybrid-3d-printer-large-format-print-test-jan-4-2018/
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I don't care what it's slingin', that sucker is fun to watch!
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@ Coffee
Of course I have fun - much of it is doing what people say you should not - don't worry about the mass, just do it.@ Joergs. A suitcase is portable and might weigh 20 to 30 kgs so.... My printer is sort of portable, it weighs a lot less than 20kgs in total - just need a big van.
@ Barracuda. Of course I can do 90 degree corners. Why would the print head overshoot? - that's a function of rigidity, not just mass.
Yes, of course it's physics and reducing the moving mass is a sound principle but only within limits. Once you reach the lower limit of practical mass for the speeds and acceleration desired or which are otherwise attainable , there is no point in reducing it further.
Like I said, do the maths. A very conservative calculation of the torque that my steppers can produce tells me that I can accelerate my 4kg mass at 1400 mm/sec^2. With my print bed size of 360mm, then in theory I could reach a speed of a tad over 700mm/sec. Reducing the mass would allow me to accelerate at a higher rate and reach an even higher speed but why would I want to move faster than 700mm/sec?
Or put another way, to reach a print speed of 100mm/sec (which is faster than most people use) at an acceleration of 1400mm/sec that speed is reached in 0.071 sec and it takes 3.57mm of movement to attain that speed. Halving the mass to 2kgs would halve those numbers to 0.035 secs and 1.8mm, halving it again to 1 kg brings the numbers down to 0.017 secs and 0.9mm. So we quickly reach a limit of diminishing returns IMO at anything below about 1kg .
Of course there are gains to be had by reducing the mass further but my point is that those gains aren't as big as most people think they are - especially when you look at the difference between say 300gms and 200gms. You are very unlikely to be able to make use of the extra acceleration that the reduced mass makes possible. Maybe on a Delta it's a necessary consideration because of the way they are constructed but if you build a rigid frame, high moving mass is not such a big deal as most people think.
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Hi @coffee,
I'm with @deckingman. Theory is great and everyone has an opinion about this or that, but there's no substitute to actually building and testing things out in reality. So keep it up!
Also, I wanted to ask if you would mind sharing your config.g? I'm curious as to how you mapped the drivers to run each pair of steppers.
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@snowcrash I appreciate those words and that is the way I feel toward others and their undertakings as well!
The stepper pairs are just wired in series and out of phase, with one pair connected to the X driver and the other pair connected to the Y driver, using splitter adapters I made up from some extension cables I had sitting around.
Below is this project's stepper wiring diagram.
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Thanks for the info and diagram, @coffee!
In terms of connecting the steppers in series, is there an advantage to hooking them up like you did as opposed to this setup:
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Most discusions I had read seemed to believe that series was better at keeping equal current to the motors and that that would be better for tourque. Actually what led me to the Duet board 6 months ago, was from this reading and it having a dual Z series connection already onboard, since with the first printer I built, I knew I wanted dual Z motors. So, since it looks like the board usese the same drivers for all, then it should be able to handle dual motors on all connections and series wired and be perfect for this concept and this is just what I chose to do. Ramble mode off...
There seemed to be 3 mindsets on this: series is better, parallel is better and both are good depending on your particular situation.
I actually have no pure technical advice on this, it's just what I felt was good for me. -
@deckingman your arguments about masses is interesting and I will rethink the opinion I have about it. But why did you separate your printer into hotend and stepper layer? I thought the reason was the masses.
One advantage of higher moving masses is that the higher mass will result in higher inertia and due to it in higher linearity of movement. I mean not only linearity in speed, but also laterally in relation to vibrations.
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@joergs5 said in Proof of Concept: The CoffeeMaker:
@deckingman your arguments about masses is interesting and I will rethink the opinion I have about it. But why did you separate your printer into hotend and stepper layer? I thought the reason was the masses.
One advantage of higher moving masses is that the higher mass will result in higher inertia and due to it in higher linearity of movement. I mean not only linearity in speed, but also laterally in relation to vibrations.
My printer kind of evolved into what it is now - and in fact it continues to evolve. I can't couple extruders directly to the Diamond hot end because the heat sinks stick out at and angle of 22 degrees, so with direct drive extruders attached (even if I could) it would just make the hot end too wide and I'd lose too much travel in X and Y.
The extruders have to go somewhere and because the bed is 400mm x 400mm, if I'd fitted the extruders to the frame, I'd have ended up with Bowden tubes at around 600mm long which I don't want. So I hit on the idea of mounting them above the hot end.
Originally, they were suspended above the centre of the bed, using pulleys and counter weights a bit like flying extruders on a Delta.
That wasn't entirely successful as the Bowden tubes were still about 300mm long. So I then decided on a separate gantry. At that time I only had 3 extruders and they were passively driven by the hot end gantry. That is to say, I connected cords between the hot end carriage and the extruder carriage. So when the hot end moved, it dragged the extruders along with it. That worked well enough and for short moves, the extruder gantry stayed almost stationary because there was some slack in the cords and the Bowden tubes took up the small moves. But at high speed and with long moves, the extruder gantry built up a fair bit of inertia which tended to try break the cords, and would have jerked teh hot end had it not been securely mounted.
At that time, the hot end gantry weighed about 2Kgs and so did the extruder gantry so about 4Kgs in total. Then when I upgraded to 5 colour, I realised that the extruder gantry would weigh nearer 4 kgs on it's own, so it didn't seem to make sense to have this dragged around by something that weighed only half that amount. That's when I added motors to the extruder gantry and created a CoreXYUV. U and V are only used for homing, after that both sets of motors are mapped to X and Y, so as far as the Duet is concerned, it's just a CoreXY when printing (but it's now using 2 pairs of motors). So in theory, I could double the accelerations that I quoted above and print even faster but what's the point? I use travel moves of 350mm /sec now.
You are correct in that one advantage of higher mass is that it damps out vibrations. I never get "ringing" or any sort of motor or belt induced ripples on the print surface and I think that's due to having high mass. With a super lightweight hot end, any vibrations, howsoever caused will get picked up by the hot end, and if it happened to be fixed with those awful groove mount arrangements, those vibrations are likely to get amplified at the nozzle tip. The higher the mass, the lower the resonant frequency so the less likely it is to vibrate.
That's how I see it anyway, but don't take any notice of me - I'm just an old guy.
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@deckingman Thank you Ian for your detailed information. I see some of your decisions clearer now.
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@coffee said in Proof of Concept: The CoffeeMaker:
Most discusions I had read seemed to believe that series was better at keeping equal current to the motors and that that would be better for tourque. Actually what led me to the Duet board 6 months ago, was from this reading and it having a dual Z series connection already onboard, since with the first printer I built, I knew I wanted dual Z motors. So, since it looks like the board usese the same drivers for all, then it should be able to handle dual motors on all connections and series wired and be perfect for this concept and this is just what I chose to do. Ramble mode off...
There seemed to be 3 mindsets on this: series is better, parallel is better and both are good depending on your particular situation.
I actually have no pure technical advice on this, it's just what I felt was good for me.Which is better (series or parallel) depends on the motor specifications, the drivers, and the power supply voltage.
With the high current low inductance motors (e.g. >= 1.5A rated current) that have traditionally been used for building 3D printers, series is better.
However,many 8-bit controller boards provide two Z stepper motor outputs wired in parallel. Some 3D printer manufacturers selling i3-style machines have realised that those controller boards can't drive two low-inductance motors in parallel, so that have chosen different motors with a lower current rating and higher inductance for the Z axis. If you have that sort of Z motor and you are using 12V power, the motors should be connected in parallel. If you use 24V power, it typically doesn't matter which you use.
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Great info @dc42 . With this stuff, finding out what to do is half the fun!
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I have one question that's on my mind: why did you implement CoreXY if you could put the steppers on the moving axes for easier construction? I thought the reason was to lower masses, but maybe your main reasons were different.
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@joergs5 said in Proof of Concept: The CoffeeMaker:
I have one question that's on my mind: why did you implement CoreXY if you could put the steppers on the moving axes for easier construction? I thought the reason was to lower masses, but maybe your main reasons were different.
Well again, it kind of "evolved" rather than being a conscious decision to use CoreXY at the outset.
When I started to design my printer, I realised that the frame would be about 600mm square. I looked at how to drive the Y gantry and decided that I didn't like the idea of driving one side and hoping that the other side (600mm away) would follow. There was too much potential for binding, flex, or other problems. I didn't like any of the belt arrangement options for having a single motor at one end for similar reasons and I couldn't see how I drive the axis from the centre. So I decided that I would use two motors - one at each end. Having made that decision, it was an easy step to use those same two motors for both X and Y, rather than add a third motor for X, which is I came to settle on CoreXY
As well as the additional cost, that third motor would be moving and so would the wiring to it. The biggest cause of unreliability that I have found has been wiring - specifically wires that move and especially where there is flex in the area of the termination. Maybe it's because I'm not that good at making crimp connections but for whatever reason, I've had a fair few failures of that sort. So that's another reason why I favoured the idea of having static motors, with static wiring.
CoreXY is an elegant mechanism IMO and has other advantages than reducing moving mass. It's been around long before anyone thought of using it for a 3D printer.
Anyway, that's how I came to use it.
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Thanks a lot Ian, now I understand your design decisions better. It is interesting to think through why something works better or not.
And if you really understand it, then - I hope - you don't make any more design mistakes when you build something new.
(My translation program insists on the german word man (which means someone) translates to english you. Is this correct? With you I did not mean you personally, but someone, you, me, or someone other).
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@joergs5 said in Proof of Concept: The CoffeeMaker:
Thanks a lot Ian, now I understand your design decisions better. It is interesting to think through why something works better or not.
And if you really understand it, then - I hope - you don't make any more design mistakes when you build something new.
(My translation program insists on the german word man (which means someone) translates to english you. Is this correct? With you I did not mean you personally, but someone, you, me, or someone other).
Using the word "you" to mean anyone is acceptable and common practice but it's not really correct and can lead to confusion. A more correct form would be to use the word "someone" which does mean "you, me or some other person". You can also use the word "one" which means the same thing, but it has become a bit archaic and not often used.
So the meaning of your sentence above would be more correct if it was:
"..and if one really understands it, then - I hope - one won't make any more design mistakes when one builds something new."
However, if you used that form of speech then some people might think that you are being pompous.
BTW, your English is much better than my German.
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My english is only better because I use DeepL often
Thank you for your explanation, my feeling that the sentence was wrong was right... -
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