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 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 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 > -- 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
