On Friday, December 17, 2021 3:02:19 AM EST John Dammeyer wrote: > Gene, > You were asking for a photo of front and back. I put them here because they > are too large to attach to an email. > http://www.autoartisans.com/harmonicdrive/GearSide1.jpg > http://www.autoartisans.com/harmonicdrive/GearSide2.jpg > > Notice how the blue and green ring gears are offset. No matter what I do > the green moves elative to the blue. Either the blue or the green by > itself with the planet gears turns smoothly with play. > They should not be moving sideways, only rotationally, and should be without any noticeable play. Make another of each ring, scaling the size down until the bottom ring fits over the 40 tooth with with a teeny bit of tension so there is no play. You should then see that by itself, it is totally self centered. Go the same for the top ring but make one at 100 teeth and one at 101 teeth. It will be a fraction of a mm bigger because the 41 tooth pinion is slightly larger. Using 100 teeth and a snug fit for no play and the gear ratio s/b 40/1
I'm not enough a math guy to know what ratio you'd get from the 100/101 combo. Also, because torque is going to want to tip the axles the pinion is turning on, that "spider" s/b a pair of disks, joined by pillars located in the outer gap between the pinions by substantial standoffs connecting the two disks. A bearing in the torrington needle style can be fitted into each pinion to reduce friction but that's for final fine tuning, For development, I'd just fit them as you have with some vegetable grease for lube, something that's similar to the crisco lard substitute for cooking. They do make a special plastic grease for this at about $15 a lb can, made by SYNCO CHEMICAL CORP in Bohemia NY, part #41160. . > Add the second though and there doesn't seem to be any clear position where > the second just drops down onto the secondary planet gears. It's always a > force fit. Either there's a key where it can go together just so perfectly > or it's a flawed design. One of the reasons to test it with the 100 teeth on both ring gears. But there does need to be just a tad of preload to the fit. In the drive I've made the ring gears are quite thinwalled radially, but are keyed and inserted into an outer reinforcing ring several mm thick. Keys are half cylinders sticking out of the edges to the reinforce surround on both inner and outer faces. And pressing the in place puts the half cylinder into matching cutouts in the outside edges of the gears. I did that so the rings are interchangeable and reverse the rotation if the rings are swapped. For some reason it runs noticeably quieter in reverse mode. Mine is much smaller, 90mm in diameter, 19mm axially . And has a 10mm hub projection to grab more of the motors shaft sticking out of the input face, with a 9mm long gt3 pulley inset and keyed into the output disk. No metallic hub or setscrew needed but I did grind a more prominant flat on the 8mm motor shaft. Driven on for a tight friction fit. > For example if I line up the blue (100/40) so the 40T and 41T gears are > perfectly aligned the green doesn't fit well. The question is how to know > where to set the gears so the 101 T slips without effort onto the 3 41T > planets. I'm not sure it's possible. One of the reasons I want you to try using two 100 tooth ring gears. If that works, then one of them at 103 teeth should work also. ISTR reading someplace that the tooth count for a 3 pinion model needed to be 3 teeth more but don't recall where I read it now. 4 teeth diff for a 4 pinion version etc. Although for a 4 pinion version I'd think 2 diff would work with the two sets of pinions placed at 180 degrees. one of the reasons I may see if I can make a 4 pinion model work when my printer is working again. . > Thing is the harmonic drive shows how the flexed cup centers perfectly at > the peak of the ellipse and on either side the edges of the teeth also meet > to take out the backlash. > > I can't see how this system does that. One of the reasons I may not use involute gears. but triangular teeth with the tips nipped, so only the side angles touch. They seem to work well in my efforts so far using a loose belt and an eccentric armature. The eccentric armature seems to give a lower impact tooth engagement but thats 100% subjective on my part. The fact that its still running at 200 to 500 revs of the driving motor for close to 90 days now seems to verify that. Will a steel one do that? IDK. OTOH, if it does break, its only 10 bucks worth of PETG and BB's. Print another. But next time I'll make it longer. & stronger. ;o) Famous last words. ;o) Take care and stay well Joihn. 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, 1940) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
