On Wednesday, December 22, 2021 7:57:56 PM EST John Dammeyer wrote: > Hi Gene, > > > From: gene heskett [mailto:ghesk...@shentel.net] > > > > On Wednesday, December 22, 2021 12:45:11 PM EST John Dammeyer wrote: > > > > 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? > > > > I've seen it someplace quite a while back. Basically you need the same > > count of teeth on both halves of a loop such as we are poking at. That > > part does change when you switch from an eccentric armature like I'm > > useing, of a 2 legged ball bearing such as you are poking at. My > > eccentric is less of a stress concentrator than your dual bearing, so > > theoretically the loose belt lasts longer. > > It's possible that vibration issues may be there if the two sides of > non-connected teeth on the cup are a different tooth count as they must be > with 147:140. So if I went 148 then it would be even. > > The thing is with just two extra teeth, to clear the ring teeth tips the > ring has to be printed with the teeth trimmed at the pitch circle height. > Andy Pugh clued me into that. Otherwise they interfere. Even the cup > could use 10% removed from the tips of the teeth. It's more critical with > 0.5 module gears than with 1.25 module gear teeth.
And much less critical when using triangular splines. there, the trim of the tips is only to prevent the tip from bottoming on the fillet the printer leaves at the junction of the two splines. Using triangles with the outer tips clipped maybe 10% the rest of the spline can be pushed into a backlash free engagement at the max radius of the eccentric without imparting any bend to the outer ring from that pressure. And the flexing of the loose belt is far less because it is only the bend of the passing wave, where the cup has to flex at the junction of ring and disk, a 3d flex instead of 2d for the loose belt. Even in the much more flexible PETG, the cup is doomed. I broke every one I made from one seemingly well designed thingiverse kit. Usually in just 2 or 3 hours. Now I have a loose belt version with a 12mm wide belt and 6mm wide rings with over 2000 running hours on it sitting on the kitchen counter. And because I wasn't sure how well the triangles would print, its only a 60-62 tooth, 30/1 design. So in addition to making the belt and rings twice as wide for the next version, I'll see how the smaller triangles of an 80-82 tooth design work, giving a 40/1 ratio. That will also need 4 of the printed bearings as they're 6mm wide ad the new armature ill be 24mm wide, a24mm wide belt, and two 12mm wide outer rings. Finer triangles means less flex on the belt as it only has to pull in less. I'd say that will allow a thicker, stronger belt. I'll tell OpenSCAD the bb's are .05mm bigger, reducing the bearing drag I get now because I made the bearing grooves too tight. That also will prolong the life of the outer race as it flexes with the belt. I made one set of those too thin and the race split it two, so I borrowed .4mm from the inside of the belt and gave it to the bearing races outer wall. End of that problem. > What I also found was that with the cup, (don't know about the belts), is > that even a very thin cup flexes in a way that only the 3 bearings at the > top of the ellipse contact the cup. The other two are redundant and the > reason they are there is because the original designer I don't think knew > any better. > > So although I printed a wave generator that used all the wheels I did some > detailed inspection and I cannot see them ever contacting. The cup is > different from the belt perhaps? Maybe the belt could be held in place by > the extra wheels but the cup is way too stiff for that. > > Stay safe > John You too John. And I hope Santa is good to you as we celebrate the birth of a baby a bit over 2000 yeas ago. 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
