> From: John Dammeyer [mailto:jo...@autoartisans.com] > > I'm headed in the other direction since I'd like LCNC to make it. First I > have to reprint the ring gear though. Would be much smarter > to actually make it with 142 teeth instead of 140. I'll try a different > filament. That will likely also make a difference and maybe > prevent the stringing. > So two more tries, one with the correct 142 teeth and still badly mangled. Tried some other slicer parameters and still bad teeth and strings. So on a "why not try" moment I switched from Slic3r to CURA. Not sure I have all the parameters the same but wow! Nice gear with 0.5module teeth. And now I have a new problem. The math for the various harmonic drives (3D printed) as shown in the attached Calculations.jpg. (140-142)/140=-0.014 or essentially 1/70th the speed of the input in the opposite direction. That makes sense since I just doubled the tooth counts from this web page. https://howtomechatronics.com/how-it-works/what-is-strain-wave-gear-harmonic-drive-a-perfect-gear-set-for-robotics-applications/ However the cup with 140T doesn't fit into the ring with 142T and the author doesn't really talk about that issue since he used 1.25 module teeth. The cup has to flex enough to so the narrow part of the formed ellipse is narrower than the fixed diameter of the outside ring gear so the teeth clear. With 0.5module and 140T the diameter even at rest is almost identical to the diameter of the 142T gear. Elongating it to be elliptical so that the two long ends can mesh with the slightly larger count gear isn't physically possible. I made up a spreadsheet to make it easier to play with values. Given my cup gear of 140T module 0.5 I would need a ring gear of 147 teeth to get an even 20:1 and the cup would flex just enough to clear the teeth. I'll post the results. Not sure what the tooth count or module is on my Brand Harmonic Drive. Quite possible they've chosen both a specific module and tooth count to get exactly 50:1 or 100:1. Playing with my spreadsheet I get the following (although I'm still using 0.5module tooth size here): Module 0.3 Tooth count on cup 400 Diameter of cup 120.6mm (not small) Ring Gear 408 Ratio 50:1 John
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