Re: Rugged CoreXY June 06, 2016 06:46AM |
Registered: 7 years ago Posts: 776 |
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hobbymods
I've gone off the idea of stackable pulleys,
Re: Rugged CoreXY June 06, 2016 08:26AM |
Registered: 11 years ago Posts: 5,770 |
Re: Rugged CoreXY June 06, 2016 08:34AM |
Registered: 8 years ago Posts: 1,873 |
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which you CANNOT DO with non-stacked belts
Re: Rugged CoreXY June 06, 2016 08:36AM |
Registered: 7 years ago Posts: 776 |
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the_digital_dentist
I've been looking at the stacked, coaxial pulley design and run into one problem with it. Using 20 tooth pulleys on the motors, when the X axis is farthest (why does that word seem so wrong?) from the motors, the belt is in grave danger of interfering with itself due to the small angle created by the small motor pulley.
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I may add one more fixed pulley near each motor, then move the motors outward a few mm to open that angle up and provide more clearance for the belts.
Re: Rugged CoreXY June 06, 2016 08:46AM |
Registered: 7 years ago Posts: 168 |
Re: Rugged CoreXY June 06, 2016 09:26AM |
Registered: 7 years ago Posts: 776 |
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hobbymods
I do get it about the twisting force in the carriage, and while the linears I'm using would probably handle it it certainly wouldn't be ideal.
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So the belts must cross like that at the front?
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Is there a solution that doesn't run the belts skewed like that?
Re: Rugged CoreXY June 06, 2016 09:52AM |
Registered: 8 years ago Posts: 346 |
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lkcl
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hobbymods
I do get it about the twisting force in the carriage, and while the linears I'm using would probably handle it it certainly wouldn't be ideal.
very very busy, partly answering dd's question as well:
...
unless the belts are offset in height (stacked one above the other - different use of word "stacked") you can NOT do the above trick which eliminates twisting force under acceleration (due to small changes in belt tension on left and right caused by acceleration force).
black and purple dots represent x-end carriage bearings, which are offset in height. mirror it on other side. sorry being very very brief.
Re: Rugged CoreXY June 06, 2016 10:04AM |
Registered: 7 years ago Posts: 168 |
Re: Rugged CoreXY June 06, 2016 10:12AM |
Registered: 8 years ago Posts: 346 |
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hobbymods
And THAT'S why he's got the X axis plate down in the hole level with the main plate, losing all that X travel, but i'm getting the same effect by running my pulleys on raised pedestals
And looking at this pic (and assuming it's done correctly) he does have the belts connected to the central carriage at different heights. Mind you he also has pieces of bronze bush epoxied to things as linear bearings.
What's the solution there that's going to work better?
Some sort of offset belt clamp/bracket?
Re: Rugged CoreXY June 06, 2016 10:26AM |
Registered: 7 years ago Posts: 776 |
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LarsK
I do not agree that this twisting force will have any effect on printer performance.
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Also, the distance between the two attachment points can be minimized to within 2mm (I say min 2 mm between running belts), no rules says the belts has to be far apart.
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The design you say will give problems is extensively used in so many printers. Remember, we are only talking about the dynamic forces from the acceleration.
Re: Rugged CoreXY June 06, 2016 10:31AM |
Registered: 7 years ago Posts: 776 |
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hobbymods
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YES! take a look at the Fusebox!!!! said it for the third time!!! *dings hobbymod around the 'earole*
I should point out that I'm 120kgs of mining contractor, which is a. why I'm dumb at this and b. why you'd only clip my earole once.
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But all levity aside, I've looked at the fusebox (very nice) previously the first time you mentioned it and again now, and my belts are run the same way it looks to me.
Problem is that I've only shown some posts without belts on them, and I've confused the issue with my misuse of the term stacking. My fault that.
Firstly my belts are stacked, one is run above the other, so we're good there.
I've got it about the importance exact 90 degrees when the belt rounds the pulley and heads along the X axis, that's how I did it.
The only difference I see is that he's used a single idler post on each end of the X axis with the pulleys on top of each other, rather than the 2 separate idlers I and the pic above have used. Which actually looks like a good way to do it.
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I thought you were saying the points where the belts fixed to the central carriage (that holds the extruder/hot end) had to be at the same height, which they are not both on the fusebox and the pic above, to avoid twisting.
I need to finish my mockup with some tape of ribbon in place so that the belt paths are clear.
So let's chill a bit and I'll put up a clearer pic in coming days.
Re: Rugged CoreXY June 06, 2016 10:40AM |
Registered: 7 years ago Posts: 168 |
Re: Rugged CoreXY June 06, 2016 11:19AM |
Registered: 8 years ago Posts: 1,873 |
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LarsK
Also, the distance between the two attachment points can be minimized to within 2mm (I say min 2 mm between running belts), no rules says the belts has to be far apart.
Re: Rugged CoreXY June 06, 2016 11:55AM |
Registered: 7 years ago Posts: 622 |
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the_digital_dentist
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deckingman
...Anyway, the reason for using 1mm pitch is that (as I mentioned), I'm planning on using the lead screws for bed levelling. It may not work but my thinking is that I have 3 point lifting so why not use it for bed levelling as well?
If the bed is going to be heated, you're still going to stand it off an undercarriage that's connected to the lead screws. Those fine pitch stand-off screws can be used to set the bed level when you first set up the machine.
Re: Rugged CoreXY June 06, 2016 12:23PM |
Registered: 8 years ago Posts: 346 |
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JamesK
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LarsK
Also, the distance between the two attachment points can be minimized to within 2mm (I say min 2 mm between running belts), no rules says the belts has to be far apart.
The attachment points on the X carriage? As far as I can see, there's no relative motion between the belts once they enter the X axis. You can clamp the belts together on the X carriage if you want. It would be cute to have the belts tooth to tooth so they zip and unzip as the roll on and off the X axis, but that doesn't seem possible with the default belt layout. But, I have no experience of building a coreXY, so I maybe not seeing something right.
Re: Rugged CoreXY June 06, 2016 01:49PM |
Registered: 9 years ago Posts: 344 |
Re: Rugged CoreXY June 06, 2016 01:54PM |
Registered: 8 years ago Posts: 1,873 |
Re: Rugged CoreXY June 06, 2016 03:13PM |
Registered: 9 years ago Posts: 344 |
Re: Rugged CoreXY June 06, 2016 03:47PM |
Registered: 7 years ago Posts: 622 |
Re: Rugged CoreXY June 06, 2016 05:59PM |
Registered: 7 years ago Posts: 168 |
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deckingman
Here are some pics of my pathetic attempt. The monstrous contraption in white is a Diamond hot end assembly complete with it's heat sinks and bits of Bowden tube sticking out. The belt layout is basically as per the reference mechanism but with one belt higher than the other which means they can cross without interference. At the end of the X axes, the bearings are stacked on top of each other which brings them closer together and closer to the centre line. I couldn't figure out a way for the idlers in the corners to be stacked on top of each other and still keep the belts parallel to the axes so they are offset as per the reference mechanism but also at different heights (to each other). I've designed the X carriage with printed ridges the same size and spacing as gt2 belt. I'm planning to pass tghe belts through the slots then bend them over these ridges and clamp them in place. There are a couple of tie rods (shown as horizontal grey cylinders) which'll be threaded rod with washers and nyloc nuts on the ends to equalise the belt tension and take the strain away from the upright parts on the carriage. Belt tensioning will be accomplished by a thumb screw which will jack the motor away from the frame (the frame mount has a slotted hole at the top but the side mounting screws will be going into tee nuts and can slide along the rails). Anyway, it all looks like it's square and parallel and all the corners are right angles where it matters. No doubt someone will step in and quickly blow this out of the water though.....
Re: Rugged CoreXY June 06, 2016 06:36PM |
Registered: 8 years ago Posts: 1,873 |
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I can see a second scrap of perspex I've got there being in mortal danger of being drawn on and cut up.
Re: Rugged CoreXY June 06, 2016 07:21PM |
Registered: 7 years ago Posts: 168 |
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JamesK
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I can see a second scrap of perspex I've got there being in mortal danger of being drawn on and cut up.
I really like the way you prototype your ideas. I'm trying to get more familiar with CAD, but I always quickly run up to the point where I want to hold it and see how it feels for real.
There's some great creative energy running through this thread, and around coreXY in general. We could really do with an 'established' reprap coreXY design (or is there one that I've missed?), but it's fun watching everyone mashing ideas around right now.
Re: Rugged CoreXY June 06, 2016 08:02PM |
Registered: 13 years ago Posts: 268 |
I've used many different CAD packages over the years, several of them professionally. To get really proficient in CAD to the point where you can design real usable parts that can be produced and assembled takes a while, and the only way to get better is practice. Most of them have pretty steep learning curves. There's some light at the end of the tunnel, I machined the parts for my delta once, and things fit and worked well the first time. I bought bearings, pulleys spacers, linear rails, motors, and even aluminum for the frame once and got what I needed. Only way to do that is by building it in CAD first, and checking everything important.Quote
JamesK
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I can see a second scrap of perspex I've got there being in mortal danger of being drawn on and cut up.
I really like the way you prototype your ideas. I'm trying to get more familiar with CAD, but I always quickly run up to the point where I want to hold it and see how it feels for real.
There's some great creative energy running through this thread, and around coreXY in general. We could really do with an 'established' reprap coreXY design (or is there one that I've missed?), but it's fun watching everyone mashing ideas around right now.
Re: Rugged CoreXY June 06, 2016 08:50PM |
Registered: 11 years ago Posts: 1,049 |
Re: Rugged CoreXY June 06, 2016 09:12PM |
Registered: 8 years ago Posts: 346 |
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cozmicray
I got a headache reading all the stuff on stacked belt bearings
a drawing of two level system
Let you guys rip it apart ????
[attachment 79368 two_level_belt.jpg]
Re: Rugged CoreXY June 06, 2016 11:54PM |
Registered: 11 years ago Posts: 1,049 |
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LarsK
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cozmicray
I got a headache reading all the stuff on stacked belt bearings
a drawing of two level system
Let you guys rip it apart ????
[attachment 79368 two_level_belt.jpg]
Nice drawings. Just, it is not that simple. The design you just sketched offset one of the idlers on the y carriages into the print area. Since this happen on both sides you loose 2x bearing size as potential print area. Using 16 mm idlers and you just lost 32 mm print area compared to if you had offset the motors outwards instead…
Re: Rugged CoreXY June 07, 2016 12:52AM |
Registered: 9 years ago Posts: 344 |
Re: Rugged CoreXY June 07, 2016 05:56AM |
Registered: 7 years ago Posts: 776 |
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LarsK
One thing nobody has talked about - Does the belt go above the rods or in between (behind) the rods.
This is my new design on one of my printers:
SO here you see the belt goes behind the smooth rod. It could also go above and under but that would take up more space and induce a bigger vertical twist
Re: Rugged CoreXY June 07, 2016 06:33AM |
Registered: 7 years ago Posts: 168 |
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lkcl
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LarsK
One thing nobody has talked about - Does the belt go above the rods or in between (behind) the rods.
This is my new design on one of my printers:
SO here you see the belt goes behind the smooth rod. It could also go above and under but that would take up more space and induce a bigger vertical twist
very nice arrangement. like the belts being the inner side of the rods. offset above and below... all belts come in on centre... yes i do the thing where the belts go behind the moving x-rods as well, that made sense to me, keep them as close to a centre-line (vertically) as possible.
what you've done here LarsK is i think about the closest it's possible to get to being balanced under acceleration and reduce acceleration-induced bearing side-wall loading.
putting the belts inboard from the y-rods also means the y-rod bearings are not torqued (side-loaded) as well, which is great.
thought about what you, jamesk and hobbymods i think mentioned yesterday, with stacked (height-offset) belts the difference in height could produce torquing of the carriage about the.... *thinks*... Y-axis under heavy acceleration. so keeping them as close together but also an equal distance above and below the line of the x rods would be good, and i think that's what you did in that new design, LarsK.
only one other consideration - keeping the centre of gravity of the carriage as close to the rods as possible *and* keeping the hotend as far up as is possible... two rather diametrically-opposed things unfortunately oh well
Re: Rugged CoreXY June 07, 2016 07:02AM |
Registered: 7 years ago Posts: 776 |
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hobbymods
Yep I'm feeling this one too.
I'm really leaning towards using 2x 10mm ground rods across the center (X) axis, there's just so many reasons.
Of course there's the fact that it'll cost 10% of what my precision rail setup would, but then there's probably half the weight, 2 less major machining/tool making steps, the ability to slide the rods out and change carriages (CNC/laser engraver attachment) and the fact that it'll probably work just as well using proper ground/hardened rod and 4x brand name LM10U bearings.
I think I'll go this way and see if it all works out.