On Mon, 3 Jan 2022, John Dammeyer wrote: > Just go back on this subject to older postings from Todd where he posted the > FreeCAD files. I then used those to create step files and loaded them into > AlibreCAD. Since then I've figured out how to make gears in AlibreCAD which > had a Python Script that used diameter and # of teeth. I modified the script > to use module or diameter. > > To create the ring gear I first create a normal gear with the right number of > teeth, module and thickness and save that. Then create a disk with the > desired outside diameter and same thickness. Then use a Boolean subtract > with the gear file. That creates the ring gear with say 60mm OD and either > 100T or 101T. > > The spur gears are created separately as a 40T and 41T with the same size > center hole and three holes to connect the two so that at one point a pair of > teeth line up perfectly. An assembly is made from those two with > constrictions to line them up. > > Then an assembly of the entire set is done. As yet I'm not clever enough to > make the assembly constraints simulate the entire planet assembly moving > around the ring gear. And the reference lines I put on mine don't actually > line up with the correct teeth for assembly. But I whipped that all up in > under an hour. > > Todd mentioned in a private email how the ratios work. > " It is because it isn't behaving quite like a normal compound planetary. > Because the planets of each set are fixed to each other, when the planets > sets orbited around the fixed ring by the carrier, the driven ring gear is > advanced by (and this is the key) the difference between the two ratios. The > result is when you turn the carrier one revolution, the planets of the fixed > ring gear turn 2.5 revolutions, therefore the driven ring's planets also turn > 2.5 revolutions, since the ratio of the output set of gears is 2.4634, the > ring is advanced the difference of the two ratios. So the final drive math is > [101/41] / [(100/40)-(101/41)]. Or 2.4634/(2.5-2.4634) = approx. 67.3. " > > It's actually 67.333... If you want to get fussy. > Here's my 3D printed version of the 150mm diameter gears. > http://www.autoartisans.com/harmonicdrive/BearingDriveShaft-1.jpg > http://www.autoartisans.com/harmonicdrive/BearingDriveShaft-2.jpg > http://www.autoartisans.com/harmonicdrive/BearingDriveShaft-3.jpg > > The bearing holds the drive centered and when the 3 planets are properly > aligned requires very little torque to move the non-fixed ring gear. However > I have not yet come up with an inexpensive way to hold that gear in a way > that it would be useful. I've been playing with a deep groove in the ring > gear and a holder outside that along with 80 of 5.5mm bearings. And a > bearing thrust washer is also needed. > > But the above example doesn't have bearings inside the planets either so it's > plastic on plastic. I can provide the step files if you wish. > > John > > > > >> -----Original Message----- >> From: grumpy via Emc-users [mailto:emc-users@lists.sourceforge.net] >> Sent: January-03-22 4:44 AM >> To: Enhanced Machine Controller (EMC) >> Cc: grumpy >> Subject: Re: [Emc-users] Harmonic Drive >> >> January 3, 2022 9:54:10 AM CET John Dammeyer <jo...@autoartisans.com> wrote: >> For fun I created Todd's version with 0.5module gears. The OD of the >> assembly >> is now 60mm compared to 150mm. It would now be possible to choose a far >> east >> harmonic drive tapered roller assembly to hold the driven gear in place. >> Although they are expensive. >> >> Not sure what type of bearings, if any would be used for the planetary gear >> clusters. I suppose one could press in bronze sleeves. I guess it all >> depends >> on the duty cycle and target application. If it's a 6 axis robot arm used >> for >> tool changing and placement/removal of milled parts then it's not running >> continuously. Might well for the home or small shop be more than adequate. >> >> This example still has 67.3333333:1 reduction but if the fit is well set then >> the backlash is essentially zero which is different from normal planetary >> reduction drives. Not sure how important that is for a 6 axis robot arm. >> >> In either case, using a 4th axis to create all three spur gears at the same >> time (one set of 40T and one set of 41 T) and then some sort of >> broaching/indexing to create the two ring gears the real issue is the outer >> bearing of the 101T output ring gear. But overall not that difficult to >> create >> once you have the 0.5 module shaper style cutter. >> >> John >> >> Where can I find more info about Todd's planetary drive. >> It looks very familiar.
I believe what he has made is a Wolfrom gear. There are quite a few variations. I made one a few years back with 45 teeth ring, 15 and 14 teeth planet, and 15 teeth sun. It had a 60:1 reduction. They are very compact. https://patents.google.com/patent/DE102019203257B3/en _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
