Ideas for the next Wally.

Re: Ideas for the next Wally.

Postby Cozmicray » Fri Apr 03, 2015 1:26 am

See:

viewtopic.php?f=7&t=30

There are many design suggestions
Many new linear Z-axis designs

Wally Chrome may be up for sale --- interested

viewtopic.php?f=7&t=28&start=10#p465

:?:
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Re: Ideas for the next Wally.

Postby realthor » Thu Apr 09, 2015 11:45 pm

Hi guys, apparently I can't give up on wally ... it should have been such a success story ...
I have thought about how to keep z movement as simple as possible while maintaining Wally ... on the wall.
I am pretty rusty with mechanics and also with design skills for that matter so I have drawn a rough sketch in Inkscape thinking that maybe someone here can take it to the FreeCAD or whatever you geniuses use.

Would this solution work? I basically duplicated the bed, reversed it, mounted the SCARA arms on this bed / ceiling, and a symmetric movement for both platforms - in opposite directions- should simulate a vertical movement on a linear rail.

This has the potential to have huge z-axis volume if I am imagining it correctly. I believe though that the platform arms can't be too long without negative effects on precision.

I have just found and downloaded "Linkage mechanism simulator" (http://www.edu-ctr.pref.kanagawa.jp/LinkWeb/index_e.htm) and will try to see how it works. What do you guys use for mechanisms movement simulations?
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Symmetrical Platform Wally
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Re: Ideas for the next Wally.

Postby Nicholas Seward » Fri Apr 10, 2015 12:08 am

We played with that. The two issues we had were syncing the top and bottom and driving it linearly. Both can be solved but were initially discarded due to complexity.

To be clear, I haven't given up of Wally's goals. I am actually starting experiements with computer vision so a machine like this can auto calibrate. (Goals: Simple, precise, accurate. Wally is 2 out of 3 and the accuracy is theoretically possible.)
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Re: Ideas for the next Wally.

Postby realthor » Fri Apr 10, 2015 12:14 am

Considering that the cost of electrical components is 2/3 of the cost of the printer, introducing web cams and faster processors/etc wouldn't just increase the cost of a reprap too much?
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Re: Ideas for the next Wally.

Postby Nicholas Seward » Fri Apr 10, 2015 12:25 am

It might be another $45 for a camera and a RaspberryPi but smart solutions are getting cheaper daily. My goal is to decrease mechanical complexity even if it increases computational complexity.
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Re: Ideas for the next Wally.

Postby realthor » Fri Apr 10, 2015 1:20 pm

Hi Nicholas, I am interested in this design, could you share your solution (here or on email if you don't want to pollute the forums with designs that you wouldn't otherwise consider because of their complexity/etc).

I am thinking of a belt gear for reversing motion:
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Re: Ideas for the next Wally.

Postby Nicholas Seward » Fri Apr 10, 2015 6:58 pm

Wally Bed.png
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Here is a slight modification of what you are talking about. You hang it from the top instead of mount to a wall. The arms with disks at the end could be spur gears or a DLCJ(Double Lamina Compliant Joint: lash the disks together in a figure-8 pattern. It has low friction and 0 backlash.). You can also replicate the arms to any of the 3 remaining sides of the bed for added rigidity. I think 1 side could be enough.

This would allow the bed to be driven with a screw or a string from a top mounted static stepper. This will also make the arm motors static or nearly static depending on how you want approach this.
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Re: Ideas for the next Wally.

Postby realthor » Fri Apr 10, 2015 8:45 pm

That's clever indeed. However such a design would require a self supported structure that would take Wally off the wall again, making it look just like any other desktop enclosure. I believe a wall mount would confer stability, rigidity against speedy arm movements/etc. Am I wrong?

I am also quite enthused about the large span the previous design could offer. I am not sure about the real-life necessity of such a large span though or if going that far apart would translate in amplifying the small errors.

Because I also want to learn to "predict" issues with a certain design, could you please give your expert opinion/critique on the flaws of the design i've proposed?

Thanks a lot.
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Re: Ideas for the next Wally.

Postby see3d » Fri Apr 10, 2015 9:17 pm

Nicholas, I like your design idea for the linear Z.

Realthor, Your previous design would be difficult to keep stable against the reaction forces of fast arm movements. It would have to be really overbuilt. The Z does not really have any reaction forces. As long as the wall or housing is stable the build platform will be stable.

Nicholas' design could be turned 90 degrees to lay flat against the wall at the back, but you would need a 90 deg wing on one side to mount a second arm to. You would want to mount the Z stepper to that wing in the middle of the plate below the arms. It could be lead screw, or string. A stepper with an integrated acme lead screw would be accurate but low speed and would hold its position with power off.
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Re: Ideas for the next Wally.

Postby realthor » Fri Apr 10, 2015 9:35 pm

Hi see3d, thanks for answering. Could you explain a bit "reaction forces of fast arm movements". I am quite unfamiliar with 3d printers precision issues, have read about backlash but that's about it. I have quite a hard time understanding the specific terms.

Thanks.
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