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snowygrouch

Throw away your short belts - direct drive.

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Hi,

Although the standard motor position is simple, easy, compact and visually neat....from a strictly performance

perspective it leaves alot to be desired.

So I thought....why have short belts between stepper and shaft...why not put the motor...ON the shaft.

Thus eliminating both short belts, two pulleys, and the compounded positional error of two rubber belts in

series.

So it just uses 2x flexible shaft couplers (5mm/8mm, with nice clamping bolts instead of horrid grub screws...YUK !)

I use one of the standard motor wooden spacers as a thermal barrier to the PLA motor bracket. The PLA mount made in thickness exactly so that an M3x16mm bolt with a washer is the perfect length to get complete thread engagement into the motor case (standard is 2 threads.....very very bad).

The shaft is 8mm (h6 tolerance) silver steel, bought in 500mm length and chopped down. Needs to be a bit longer

than the standard ones.

I dont realy have any comparative data on accuracy, but I sleep much better knowing that the two short belts are in the bin.

Further data available to interested parties.

Calum Douglas

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Mmm well it wasnt expensive at all to be honest. Here is pretty much what I paid.

Flexible couplers 5Euro each (I bought a whole load because I liked them so much)

8mmm h6 shafts 6Euro each

COUPLERS>

http://www.ebay.co.uk/itm/130707094693? ... 388wt_1139

500mm shafts, cut down to APPROX 370mm>

http://www.conrad.de/ce/de/product/2372 ... Detail=005

I spent alot because I bought quite a few couplers, and also bought some shafts which sucked and then had

to re-order etc.

so all in..

I suppose 40 euros for both axis by the time you pay tax+delivery.

Well worth it I think. I just did the X axis tonight (pics taken on 1st print ! after ditching the X belt!) so will try

another print later this weekend after both axis are done. I am anticipating a noticable improvement in

layer alignment as well as the possibility to increase speeds in future.

I wont send you the STL of the bracket because its rubbish, I need to modify it so it prints with no support.

Once I do a rev 2 bracket tomorrow morning I will happily email anyone the STL. The bracket uses just two

of the standard holes. So no frame mods required !

I was expecting the couplers to be a bit rubbish (from China etc), but for this application they are more than

adequate. If I was building a machine for Siemens or somthing ok I would be paying 100euro a coupler...but Im not..

and these are perfectly functional for these loads and speeds. It did take 4 weeks for the couplers to arrive though...which was maddening.

C.

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Really really nice idea about taking the rubber out of the quation and making it direct drive.

typical great idea. every one rubs their head and says, why didnt we do that from the beginning ?

Cant wait to get the idiots guide to build this..

ill be happily the first idiot to make this change !

thanks a million and best wishes from Leipzig.

Ian :D

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Its a very neat design, but in my perspective it ads too much on the sides of the machine could increase likelihood of damage during transport.

Im thinking: place the steppers on the inside, pointing upwards and have a shaft and fine-tooth gears to directly link it up.

now that im typing this, most likely you will loose allot of accuracy since the gears don't match up perfectly...

What about small chains? instead of belts.

just my input.

keep up the great ideas, somday it will make it into a new ulti kit or different product

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just a question about the question.

in all honesty ? how many times are we going to move our ultimakers.

I know for myself, I received my ultimaker, built it and both of them are standing where they were built... happily printing.

the idea is clean, simple and needs no big cutting and glueing changes to the ultimaker.

an idea that could ! be addopted in future versions of ultimaker !

Ian

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in all honesty ? how many times are we going to move our ultimakers.

I know for myself, I received my ultimaker, built it and both of them are standing where they were built... happily printing.

Depends on the user. I had a week where I left my UM in the Car every day when I got home, because I knew I would take it with me again the next day.

For some it's an issue, for some not.

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Hi Guys,

Its definetly a bit ugly, to have two "blobs" sticking out the side of the machine, and I did bang one of the motors into the wall last night....when I do overnight prints I put the printer in the hallway behind a curtain to keep the noise down...so I do move it occasionally. However to be honest if you are stupid enough (like me) to bang into

a wall, you deserve to have a broken machine ! However the difference is exaggerated because of the heatsink and fans on the rear of steppers. Also this is a rev1, design: I could probably shave off 5mm more. The fans keep the steppers so cool that the wooden "heat insulation" spacer is really doing nothing.

If I knew how to make the motor turn the other way, you could put one motor at the back instead of sticking

out the front. Which would be a little neater.

Overall Im still very frustrated because I now have mechanically a very good printer, but I dont have alot

of experience with it so I dont really know how to set up the various Slicer programs to get good prints and so on.

I had to kill a Netfabb print last night after 20mins because the bottom few layers were just complete rubbish,

the head was scraping so much on top of the previous layer that it was almost chewing it up. But I digress....

So if someone wants to help me with some accerated Netfabb learning, I will happily make up a complete build

document for the direct drive setup or perhaps even send you some parts !

Calum

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I can offer you all the assistance you need with k'slicer if you like. as far as I know, netfabb doesn't support retraction properly anyway so isn't the flavor du jour.

whilst fully capable of making the mods myself, I have no bandwidth to do them right now until I have my new hotend sorted and I think some 'instructions for dummies' might be a really useful contribution to the community anyway.

drop me a PM if you like and I can send you some screenshots. it's generally easiest to solve these problems visually.

nik

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Dear all,

Please find attached .pdf file (put in a zip archive because you cannot upload .pdf extension files here).

Also attached is STL for the motor bracket (zipped as per above).

Its the same part for both motors, so do not be alarmed by seemingy superflous holes. Print x2.

I edited the bracket last night so it KINDOF prints without any support if you print it with the

small face down and the big "foot thing" face up.

Have fun !

Calum Douglas

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Regarding reversing the stepper - swap the wires between the A and B drive coils, it runs backwards.

Or just reverse the two wires of one of the drive coils. Again, it reverses.

http://www.nmbtc.com/step-motors/engine ... uence.html

I see someone found that their RepRap feeder motor reversed just by reversing the plug. A bit risky if you don't check and confirm the wiring first.

http://www.nmbtc.com/step-motors/engine ... uence.html

 

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In another post, I tried to describe a mathematical model to describe my error:

Final Position (along one axis) = (Xo) + Etiming + Elong

Xo = what software considers the initial position

Etiming = Positional Error due to (1) Slip of timing belts and (2) Improper Orthogonality of Timing Belt to Long Belt

Elong = Positional Error due to (1) Slip of long belt, (2) Improper orthogonality of both long belts

(Also errors due to parts not being screwed in tight but is removed due to simplicity)

Would you agree with this simplistic description?

I also came up with what I consider to be a reliable calibration method: UV LED coupled into a fiberoptic cable that is mounted on the moving head. The beam diameter of the resultant light determines the precise resolution of this method, but with proper optics can probably be put to at least 10um without significant costs. On the build platform, place a sheet of the UV-reactive copper used for etching circuit boards in the 70s. After drawing shapes using Gcode, put the copper under a microscope (with calibration distance lines built in) in order to properly test positional accuracy.

How do you feel about this? I would be very willing to put one of these systems together if it means I can get some real numbers behind my positional accuracy.

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I understand what you propose to do, but I do not think there is any point in measuring the printers product so accurately.

The bed moves around about half a mm at the front under severe jerk forces during printing, the frame is made of wood, which will be expanding and contracting with humidity all year round, the printhead basically just a very small

icing-cake squirter which will produce a different width of bead depending on filament diameter (varying alot even over just one long print) and so on, and so on. I think your measurement accuracy will dissapear into the noise of all that going on at once.

I would honestly just make yourself some nice geometric primative shapes, print them and measure with a nice set of Mitutoyo vernier calipers, which are far more accurate than the error of the machine itself.

If you want to measure it all optically then fine, but I think your efforts will be spent unwisely !

If you have access to all that nice equiptment, just make the machine better. You dont need a microscope to tell you that having one belt instead of 2 in series will be considerably better.

If you really want to do your experiement then I will enjoy reading the results.

Regards

C.

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Thanks for the quick and thorough reply, however a few things:

(1) "The bed moves around about half a mm at the front under severe jerk forces during printing"

Is the jerk force in the direction of the Z-axis twist? If it was possible to add two more rods and linear bearings to the front could this be accounted for and removed? There's definitely room for it, that's for sure.

(2) "the frame is made of wood, which will be expanding and contracting with humidity all year round"

I will be recasting all of it into acrylic so I can do cellular printing. I will also be changing the printhead to a cell droplet mechanism so the filament thickness doesn't matter here.

(3) I would honestly just make yourself some nice geometric primitive shapes, print them and measure with a nice set of Mitutoyo vernier calipers, which are far more accurate than the error of the machine itself.

I don't think that printing filament would be a good calibration approach, since not only does it shrink (even if only a little), but the thickness of the strand I print is far larger (I believe) than the positional accuracy I am trying to measure.

I don't see how I can design a gel-droplet slicer software that will provide me prints that are accurate enough to facilitate cell-cell recognition unless I am positive that the positional accuracy of my printhead is within reason compared to my droplet size. My only point of concern is that I see no evidence of any record of positional accuracy measurements (except for a random article I stumbled upon on the topic of Ultimaker calibration but was completely in German :\ )

Thanks for your time,

J

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that's one more article than I ever saw then. there are plenty of claims about resolution to 40 microns, but be wary, what you can do in Z you cannot do in X and Y, and what is claimed in any is often for a Yoda head, not a precision calibration object.

If I had to write a spec. for UM I'd say you can do 100 microns on a good day if you know what you're up to and set the machine up nicely.

I'm hoping someone will challenge me and say, no, UM can do so much better, at which point I'll ask them to print and show us all a calibration item that proves it, and then I'll buy them a beer, or maybe even two, depending on how generous i'm feeling.

but now, back to reality..

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We could replace the long belts with something less stretchy. There are higher quality toothed belts with less give, I'm just not sure where to find them.

Ballscrews or acme thread could replace the long belts, but it would take two for each axis. It would change things a bit in terms of the driver PCB, although it could be done as an add-on. I think it would be a rather significant change. Speed is an issue, so I don't see hardware store allthread being a solution, however I've not run the math.

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Ballscrews would be pretty sweet. Expensive though... the cheapest I found on Ebay now was $35 for a 25cm screw with nut. The ballscrews I've seen on Ebay seem to have pretty low pitch though so speed could indeed become an issue.

Speaking of ballscrews, I have a few lying on the living room floor together with aluminium profiles, drivers and steppers. etc. it's supposed to become a CNC but... hasn't moved for three years now. $2000+ just lying there lol.

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