GUS Red build log (aka SpiderPig)

Re: GUS Red build log (aka SpiderPig)

Postby Nicholas Seward » Tue May 27, 2014 5:41 pm

Well. I have about 70mm or so from shoulder to hub in the z direction. That minus 12.7 minus 3.8 is about 54mm. (It is possible that you putting in 76-77 allowed it to find a local minimum that was far away from 54 so that could explain the elongated z.)

I am not sure what you mean by "overlapping wraps". I don't see the M8s moving during tensioning but now that I have had my system tensioned for a long time I can see that the M8s have migrated away from the intended location. Three things will not exist in future versions. 1) cantelievered bolts. 2) string sliding directly on metal. 3) printing gears with their axis orthogonal to the print head.
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Re: GUS Red build log (aka SpiderPig)

Postby brandonh » Tue May 27, 2014 6:48 pm

Thanks, wasn't sure about that one, but it should explain things.

By overlapping wraps I mean one string crossing over another in an X shape, versus parallel lines.

When you say "shoulder to hub", which surface you mean exactly? I assume "to hub" means "to centerline of hub m8 screw".

It sounds like I'm coming in a little late to the party, where the flaws are mostly known. Aside from linearity measurements on the 3 arms post-calibration and trying without a spring, is there any data that would be useful to inform the next arm design, which my GUS could help find?
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Re: GUS Red build log (aka SpiderPig)

Postby Nicholas Seward » Tue May 27, 2014 7:28 pm

I don't have crossing of the string but I don't see that causing much of a problem.

offset.png
offset.png (248.4 KiB) Viewed 14807 times


Here is an illustration of the hub to shoulder measurement. (Again, the closer this number gets to zero the more the singularity plane will mess with you.)

I just (last week) discovered a way to get all the benefits of the gear arm without the gear. (That is sad in a way but good in so many others.) I will post when I get some renderings. Just keep an eye out and you can offer some good feedback. (It seems like the machine wants to look as much like a Simpson as possible.)
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Re: GUS Red build log (aka SpiderPig)

Postby brandonh » Thu May 29, 2014 5:35 pm

So after some nice printing on Monday, of an unintentional slinky and an intentional squirrel, I went to the local RepRap meetup yesterday. I didn't think it was a particularly warm day, but I probably should have parked in the shade.

See:
https://plus.google.com/104919785646757 ... uwQWBwknkG

The extruder is fine and the shoulders might be usable but everything else is twisted beyond repair.

Oh well. First-world problems: your 4th 3d printer melts.

I learned most of what I was going to learn from this one. Basically, confirmations of known problems: rough gear teeth due to vertical printing orientation, unwanted friction from spectra riding on directly on m8 bolts, and hysteresis/nonlinearity that results from both. But these are all balanced by confirmations of overall bad-ass-ness :-)

Nicholas, you've been dropping hints of a better way to do the arm. I'm game to take a sketch/screenshot and turn it into an Inventor model and then functioning arm.

Thoughts?
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Re: GUS Red build log (aka SpiderPig)

Postby Nicholas Seward » Thu May 29, 2014 6:16 pm

I will make some sketches and post if you want to get a jump start. I plan to be testing arms next week.

Sad to see it melt like that.
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Re: GUS Red build log (aka SpiderPig)

Postby brandonh » Thu May 29, 2014 7:03 pm

That would be great.
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Re: GUS Red build log (aka SpiderPig)

Postby NeoTheFox » Thu May 29, 2014 7:06 pm

Image

This one... I cant stop but laughing, I am sorry.
Good luck with a new prints, you have had the best quality I've seen on GUS.
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Re: GUS Red build log (aka SpiderPig)

Postby GrahamHolt » Sat May 31, 2014 7:57 pm

@brandonh
Sorry to see that your printer melted. You mention the spectra running directly on the bolts being a problem, and I've been wondering about that. The bolts I've sourced are new, but a little beat up. I'm worried about little nicks cutting into the line. Hopefully I'll be able to remove the imperfections with a little fine grit sandpaper. Any thoughts on this are appreciated.

@nicholas
Very interesting about the gearless arm design. I've been able to find a few decent books on the engineering front, so I'm looking forward to the next round of idea bouncing.
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