Gene, just don't worry about failure on these. These are aerospace grade machines and you buy them cheap on eBay. Even if they did fail it is not a safety issue. You just say "It broke" and fix it.
The other parts I found on eBay are worm and wheels. They are already machined for connecting to stepper motors. gear ratios are up to 1:100 www.ebay.com/itm/NEMA23-030-Worm-Gear-Reducer... <https://www.ebay.com/itm/NEMA23-030-Worm-Gear-Reducer-NEMA23-Ratio-10-1-15-1-30-1-for-Stepper-Motor-New/122400098796?var=422875302545&_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D49566%26meid%3D2819f38fae6d49dba8e5fcf48b9649f5%26pid%3D100005%26rk%3D6%26rkt%3D6%26sd%3D122401339155&_trksid=p2047675.c100005.m1851> I wouldn't bother with blender. Fusion360 is better for this kind of work. But if you need Blender, for say making characters for a video game get it at blender.org On Fri, Dec 15, 2017 at 1:24 PM, Gene Heskett <[email protected]> wrote: > On Friday 15 December 2017 14:20:27 Chris Albertson wrote: > > > If the goal to build a zero backlash rotary table the gold standard is > > a "harmonic drive". These are simpler designs that are inherently > > near zero backlash, typically at the arc second level. It works on a > > similar principle -- a ring gear and another gear with one less tooth. > > These devices just blow away any worm and wheel. > > > > https://en.wikipedia.org/wiki/Harmonic_drive > > My personal objection to the normally built harmonic drive is two fold, > first being the up front expense, and second, the flexing of the outer > gear has to have an effect on its working lifetime. Even if the flexing > of the rim is well within the elastic limit of the steel, the stored > stress will lead to a crack failure at some point. Might be several > millions of cycles, handily outlasting me and my great grand children, > but. I have heard, not recently, of a rifle action failure when it had > never been 'overloaded' due to the buildup of stored stress. Its said > perhaps 20,000 rounds or less for the larger, and higher pressures > developed cartridges, up to perhaps 100,000 rounds for a lower pressure > cartridge such as a 30-30. Any of those figures will outlast the barrel. > OTOH, my P17, an Eddystone action thats famously hard and therefor > brittle, has gone thru its 5th barrel, and close to 20,000 rounds, most > of which were 60kcup+ Ackley-06 loads. So its 6th barrel I just put in > it, is chambered for the somewhat lower powered 6.5 Creedmoor. > > > THIS is the project I want to copy https://youtu.be/mmOnktzifeg and > > here is part 2 https://youtu.be/xaEhkF9S0mY Excelent videos > > > > If I could find a harmonic drive cheap enough or if I could make then > > want 7 of them for a 7 DOF robotic arm. My current arm uses model > > airplane serves and has a 1/2 to 1/4 inch position error and very > > little payload ability. > > > > Autodesk Fusion 360, an animate parts too. That s what I use. It is > > it's free (until you use it to make $50K gross income) and prefect for > > the above. Yes can output g-code for mills and lathes. > > https://www.autodesk.com/products/fusion-360/overview > > > I just pulled in blender, but its an older version, can import, but not > export, .svg's. And inkscape can I am told, then export the g-code. > How well that works is TBD. I think there is an export .svg option thats > installable, but haven't found it yet. Might take a newer version of > blender, there have been 14 point releases since the debian repo > version. > > > On Fri, Dec 15, 2017 at 10:09 AM, Gene Heskett <[email protected]> > wrote: > > > On Friday 15 December 2017 11:11:32 John Kasunich wrote: > > > > On Fri, Dec 15, 2017, at 06:16 AM, andy pugh wrote: > > > > > If you look at stock internal gears: > > > > > http://www.hpcgears.com/pdf_c33/17.7.pdf > > > > > You will find that getting a pair that differ by only one tooth > > > > > isn't that easy. And they will differ in PCD. The PCD difference > > > > > isn't to hard too deal with in external gears if you can make > > > > > them big enough for the corrections not to distort the teeth too > > > > > much, but it would be much easier to not have two PCDs on the > > > > > planets. So, you would ideally be making your own internal > > > > > gears. > > > > > > > > I believe it would be possible to design a similar drive using the > > > > same internal gear for both the grounded ring and the output ring. > > > > All the gears would have standard tooth forms, and could be > > > > off-the-shelf. > > > > > > > > The trick is that the planet gears centers would have to be at > > > > different radii. So instead of the two sets of planet gears > > > > running on the same planet carrier pins and being fastened to > > > > each other, you would have two sets of planet carrier pins > > > > (probably on opposite sides of a planet carrier plate). The > > > > planets would all be independent. One set would have N teeth, the > > > > other set would have N+1 teeth. The sun gear would be two stacked > > > > and coupled gears, one with M teeth (meshing with the N tooth > > > > planets) and one with M-2 teeth (meshing with the N+1 planets). > > > > > > > > Not sure if what I'm describing is still a wolfrom drive, but it > > > > would have the same result - a very high reduction from planet to > > > > output ring. > > > > > > That sounds like a quite practical thing once the math has been > > > worked out. And it also sounds like it would be a heck of a lot more > > > efficient assuming the planets were running on caged needle > > > bearings. Ratios high enough they could be a rotary table drive, and > > > most certainly less backlash than my current 4 incher has which is > > > tight at some positions, and a good degree at others. I just > > > yesterday watched a guy build a std planetary set using blender, > > > which in turn allowed the wireframe to be animated for proof of > > > concept. I had no idea blender had all those capabilities. I believe > > > it can actually export g-code too. > > > > > > But something along these lines, using gears maybe 1/4" long, sounds > > > like it could be stacked in a rotary table casting, one that could > > > be moved by a nema23 motor while resisting cutting forces. Mine > > > can't even do that when stationary due to the backlash. Piece of > > > junk from India for a smidgeon over a $100 bill today, I doubt its > > > accurate enough to do a usable gear. Those 1/8" thick, #25 chain > > > sprockets I made that one of you kind folks wrote the gcode for me > > > several yeas ago, I cut with a new 1/8" 4 flute carbide tool, and > > > due to it moving to the other side of the backlash on opposite faces > > > of the tooth, cut the teeth wide enough that I had to file the wider > > > part of the tooth about 4 strokes of a fresh mill bastard on each > > > side of the tooth before the tooth would properly enter the > > > inter-roller spacing of the chain. And while it still runs "lumpy" > > > it does get the job done, which was driving a taller fence with a > > > couple pieces of 1/4" redi-thread on my bandsaw so I could move the > > > fence while maintaining the drift angle well enough to cut about > > > 3/16" slabs of butternut out to make panel inserts for all our > > > kitchen cabinets. Butternut I got from Ray Henry on one of my trips > > > to the UP. > > > > > > I am "intrigued" if you've time to hack up some drawings. I have > > > 1/2" thick micarta which could be used for a proof of concept. > > > Highland Hardware in Hotlanta has more of it. And I have about 8" or > > > so of 1" Acetal rod for the planetaries. I bought it to hot mold > > > zero backlash nuts from, then bought some teeny ball screws instead > > > from Stuart S. > > > > > > Heck of an idea John. > > > > > > Cheers, Gene Heskett > > > -- > > > "There are four boxes to be used in defense of liberty: > > > soap, ballot, jury, and ammo. Please use in that order." > > > -Ed Howdershelt (Author) > > > Genes Web page <http://geneslinuxbox.net:6309/gene> > > > > > > ------------------------------------------------------------ > > > ------------------ > > > Check out the vibrant tech community on one of the world's most > > > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > > > _______________________________________________ > > > Emc-users mailing list > > > [email protected] > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > Cheers, Gene Heskett > -- > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author) > Genes Web page <http://geneslinuxbox.net:6309/gene> > > ------------------------------------------------------------ > ------------------ > Check out the vibrant tech community on one of the world's most > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
