Core XE Bot

Discussion in 'General' started by Josh, Jun 16, 2014.

  1. Josh

    Josh Administrator
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    Tim Rastall, Sanjay and I have been working together on the design of a new bot - which I have nicknamed Core XE.

    The main feature of the design is that it enables you to get the extruder motor off the carriage, but keep the drive gear on carriage. This gives you the lightweight advantages of a Bowden system whilst giving you the precision of a direct. Magic! The trade-off is that you then have a more complicated belt and motor arrangement which is shown in the image below.



    I will let Tim post photographs of the bot below when he has a moment. In the mean-time, there was a 3D Printing Hangout where Tim and Sanjay introduced the design: http://youtu.be/rAhpKY6Iwso?t=29m20s

    We have put quite a lot of thought into how belts, shafts and motors should be arranged already and this has gone into the design that you see, but we certainly welcome feedback!


    I have been focusing on the design of the extruder and evaluating the practicality of the design as a whole.

    Carriage
    The carriage uses a pulley to transmit torque from the belt into a shaft (right), this torque is then rotated about 90° and geared using a set of bevel gears with a 2:1 ratio. The pinion turns the larger bevel gear which is mounted on a hobbed shaft. The hobb then drives the filament down into the HotEnd.



    On the left there is an idler bearing. Depending on how this version performs, I am considering using a second pulley and gear pair on this side, this would keep the forces in the belt more balanced on both sides however would mean a larger mass for the carriage so is something I would like to experiment with going forwards!

    Motors
    If you looked carefully you will have now noticed that if the belts teeth run over the extruder drive pulley then the belt is actually running smooth-side over the motors. Tim's idea is to use another 2x bearings per motor to ensure that it runs over the correct side of the pulley and so the teeth engage.

    The motion of the motors will clearly be linked to movement in X, Y and E - I have done the maths to establish the worst-case scenario in terms of maximum speeds and forces at the motors given the demands of the 3 axis. The hard part is balancing the gearing ratio at the extruder. It is important to find a sweet spot where there is enough force at the extruder whilst not gearing so heavily that the belt-speed required becomes too high for the motors to be able to keep up.

    I am going to do a bit of work on the document where I have set it all out (including resolution and acceleration) so that it is all a bit more readable and then I shall post it so that my logic can be checked! :p

    When I was doing some research, I came across some similar ideas out there which are interesting to have a look at in context of the Core XE Design:-
    http://www.thingiverse.com/thing:15132/#comments
    http://garyhodgson.com/reprap/2012/01/e ... der-motor/



    At this point I would like to ask what your thoughts are? It's a bit of a crazy idea and I would be really interested to hear what everyone's thoughts are on the balance of the benefits versus the added complexity?

    Going forward Tim and I are hoping to get more people involved in the design process to speed things up a bit. (Currently all files are in Rhino and Inventor). If anyone is interested let do let us know! :)

    Cheers,
    Josh
     

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  2. Eaglezsoar

    Eaglezsoar Administrator

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    Fantastic design, I do hope you carry this out to fruition, it could change a great deal in the world of 3D Printing.
     
  3. Dejay

    Dejay Member

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    Damn I had a very similar idea I swear lol. My idea was to create an additional path for spectra line / belt though, basically sitting "on top" of a CoreXY belt path. Or even having two extra paths for two extruders / multi extruder with a selector cam. The main problem with this kind of thing is of course that you couple the position with the extruder and have to move the extruder motor to compensate and that this might create some kind of "unsynchronized" pressure in the nozzle and jitteres in the extruded filament. I guess one would have to try, the pressure in the nozzle might be "elastic" enough to compensate.

    An alternative to have a light but "direct" extruder would be the Flex3Drive from mutley3d.com I guess. Maybe there would be a possibility for collaboration?
     
  4. Nicholas Seward

    Nicholas Seward New Member

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    I think this may be a more sane arrangement. This will keep the anti-racking of the CoreXY design and will allow you to use string for the XY motion keeping it very light and robust. (My philosophy is to use string when you don't need continuous rotations. It is 100lb test for gods' sake, cheap as f$%k, easy to route, and easy to tension with a guitar tuner. The E will be the only one that needs a continuous belt. It can be tensioned with the secondary pulley on the effector. Additionally, the corner without a stepper is begging for the Z stepper. (Some pulleys are shown sharing the same axis as others but depending on what pulleys you want for the string and the belts this doesn't have to be the case.)


    You could even run the Z like the E with a T-bot style mechanism on the effector. (That is clearly against the goal but I thought it was worth mentioning.)
     

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  5. Josh

    Josh Administrator
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    The main issue that I had previously was that the high precision requirements of X and Y with the high torque requirements of E.

    As I mentioned over on G+ and in my above post, I did a bit of maths on this http://files.e3d-online.com/ExtruderSpeed.pdf and it looks like it should work if the gearing ratio at the extruder is around 3.. but then the concern is that the internal forces could cause issues - Tim and I were about to put one together when we just ran out of time.. :/

    In your arrangement these systems off the same belt which is a start, but the E-belt obviously still needs to be able to keep up with the X/Y Carriage.. I need to sit and think about the implications of that to get my head around it.. :p I am keen to just build it..
     
  6. Timrastall

    Timrastall Member

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  7. Dejay

    Dejay Member

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    Nice design!

    I was thinking about string and wondered if one couldn't just use a driven pulley with a adjacent neighbor idler pulley to wrap the string a few times crisscrossing between them. Then the string could run in circular grooves on a pulley instead of a spiral and wouldn't run up and down. This might increase overall friction but might make larger or continuous linear motion possible with string without running "out of pulley space". And it might increase precision because the string doesn't move laterally. You could tension the string by moving the neighbor idler pulley apart.
    EDIT: Hmm, on second thought the weakness of something like this would be that you'd have a knot in your string loop that would at least be a weak spot and at worst could jam in between the pulleys.
     

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