> From: gene heskett [mailto:ghesk...@shentel.net] > > On Wednesday, December 22, 2021 4:24:30 AM EST John Dammeyer wrote: > > Here's the 140 Tooth cup and 147 Spline for a 20:1 ratio with 0.5 module > > That's a rule violation for a two point drive, the count diff must be a power > of 2. What rule? Where's it written? Why?
For a triangular wave with three bearings, a diff of 3 is required to > keep the belt centered. I suppose one could use a 90 degree, 4 bearing > generator with a 4 tooth diff but haven't tried it. I'm not using a belt I'm using a cup although I suppose it doesn't matter that much. > > With 140/142, it would a 70/1. ratio. 140/144 would be 35/1 At 140/147, you > can see the off center in the much smaller gap at 11, compare to the much > larger gap at 5 oclock that you can see. 140/142 is 35:1 in a cup drive. The 140/147 is 20:1. (140-147)/140= 0.05 inverted is 20:1 > > In my experiments I found a 4 count diff very difficult to get right w/o more > eccentricity in the wave. Which leads to broken belts even in petg. It's true there isn't an equal offset between cup teeth and ring teeth. What I'm finding is that the 0.5 module 3D printed teeth are of course not perfect and just a tad thick which means they fit much tighter than they should. The PLA cup is also a hair too thick in body and doesn't flex as much as I'd like. For the original I've printed a PETG one which is much better but I haven't yet tried it. Not really set up to do continues running testing. The cup with random layers came out much nicer but I haven't removed all the support material yet. I may just turn a jig that lets me hold the cup tightly in the lathe so I can clean up the inside and shave it down. As for lifetime as the robot arm joint of a tool changer and product placer I don't see any value in it running for 1000 hours. Would be more worried about the plastic taking a set after sitting idle for 3 weeks in one position. Which is why I like the outside wave generator far more than the inside wave even though it's larger. As I have a set of 0.5 module involute gear cutters and anything over 135 Teeth is essentially rack to get the cad software to create the rack profile I need more than 135T which is why I chose 140. I'm not convinced that a different gap between the two bearings in the wave generator should make any difference. John > > > gear teeth. No backlash in fact a bit tight. ID of cup is 68.5mm so a bit > > smaller than the original one (82mm ID) with the big teeth and 1.25 module > > (36:1). > > > > Only problem is the cup gear layer changes were all in one row and it's made > > more of a dip than bump and the bearings do hang up a bit on it. > > > > Funny thing too. The wave generator disk looked like crap and the bearings > > wouldn't fit on their posts with Cura but came out nice with Slic3r. The > > cup is Slic3r. The spline done with Cura. > > > > http://www.autoartisans.com/harmonicdrive/HM_Drive-140T0.5M.jpg > > > > I'm going to try and reprint the cup with random layer changes to try and > > get rid of the bump. Should be able to mount it into the existing box and > > lid and try it out. > > > > John > > > > > > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > 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, 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 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
