Encoders have gotten very easy and cheap. These are small enough to fit inside the drive, and only cost $9 on Amazon. They are half this price if bought directly from China and even less if you have custom PCBs made. This chip on a custom PCB might cost about $2 (plus about $25 in express DHL shipping) But Amazon can ship next day with Prime. I've kind of gotten spoiled with "next day" shipping. www.amazon.com/.... <https://www.amazon.com/%E3%80%90%F0%9D%90%84%F0%9D%90%9A%F0%9D%90%AC%F0%9D%90%AD%F0%9D%90%9E%F0%9D%90%AB-%F0%9D%90%8F%F0%9D%90%AB%F0%9D%90%A8%F0%9D%90%A6%F0%9D%90%A8%F0%9D%90%AD%F0%9D%90%A2%F0%9D%90%A8%F0%9D%90%A7%E3%80%91-Accurate-Convenient-Brushless/dp/B08MDSP47L/ref=asc_df_B08MDSP47L/?tag=hyprod-20&linkCode=df0&hvadid=476098261137&hvpos=&hvnetw=g&hvrand=11652385429783510956&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9031026&hvtargid=pla-1167859449320&psc=1>
I'm looking to make a reduction drive too, but I can't use a stepper-driven harmonic drive. I need only 1-:1 reduction and the ability to back drive. But in either case, these magnetic encoders beat the bulky mechanical ones and (1) they are absolute position, not incremental and (2) they don't need quadrature logic to decode, they output I2C (3) 12-bits of position resolution (4) magnetic connection. So there is no need for a shaft coupler, The best place to close the position loop is inside the driver, going through software in a PC introduces performance-killing delay. On Fri, Dec 17, 2021 at 4:14 PM John Dammeyer <jo...@autoartisans.com> wrote: > And now with the 40T and 41T labels on each gear it was possible to spin > them on the mount so they were all in the same orientation and I then > constrained one mount hole on each. Then repositioned the teeth and the > two rings. Now they all match back and front. > > Have not yet figured out how to set up constraints so the gears turn with > each other. Of course the 3D prints take care of that exercise. > > Now as an aside would it be more prudent to work an encoder into the green > output gear for feed back into LCNC or for that matter the motor driver? > (With the appropriate division ratio). > > John > > > > -----Original Message----- > > From: John Dammeyer [mailto:jo...@autoartisans.com] > > Sent: December-17-21 3:43 PM > > To: 'Enhanced Machine Controller (EMC)' > > Subject: Re: [Emc-users] Harmonic Drive > > > > Here are screen shots of my drawings as imported from the FreeCAD STEP > files. The first thing I did to them is add a pattern of 3 > > holes evenly spaced 120 degrees apart. When I redo these I'll go from > an equilateral triangle to a form that only allows one way to > > screw them together. Then it won't be possible to connect them any way > but the way a dual extruded version would go together. > > > > In my case here, the key hole is on the X axis for both gears so > connected like that the gear teeth at that position line up too. Hard to > > screw that up. > > > > More difficult is seeing the positions as you showed in your last > sketch. Adding the Teeth number engraved into the gear opposite > > that tooth allows a user to line up the text horizontally. > > > > But change to an isosceles triangle for the hole and identify the gear > top side with the text and now even without markings it's easy > > to see which screw should be on the right side with the text line > parallel on each. > > > > Or just create a jig that goes into the bottom of the 40T planet > arrangement holes. This would hold the gears in the correct > > orientation while being inserted into a more complete housing holding > the ring gears. > > > > In either case, the assembly rotates smoothly now. Just need to make > something that holds the planetary cluster in frame with the > > fixed 100T gear. > > > > John > > > > > -----Original Message----- > > > From: Todd Zuercher [mailto:to...@pgrahamdunn.com] > > > Sent: December-17-21 8:10 AM > > > To: Enhanced Machine Controller (EMC) > > > Subject: Re: [Emc-users] Harmonic Drive > > > > > > Here is a better image with the clocking points marked on the pinions > to better illustrate what I mean. > > > > > > Andy, I think what you are describing is what I did with my first > drawing (with four sets of planets). When the rings have the same > > > diameter but different tooth counts, you have to fudge the module (and > probably the tooth profile) of the rings. (The version of > > > Freecad I'm using doesn't give me the option to mess with the tooth > profile.) With that set up all of the pinions would have the > > same > > > tooth counts. And in the case of a 1 tooth ring count difference, one > of the planet sets would have no phase shift and could be a > > > single gear double tall. But all of the others would have different > shifts. For a 3 planet the shift would be +1/3 tooth for one set > > and > > > -1/3 for the other set. This set up has exactly 1 tooth per spider > rev reduction. > > > > > > I dropped the identical ring size version when I discovered that > making the pinions 1 tooth different made up for the 1tooth > > > difference in pitch diameter of the rings, because I didn't like how > the fudged module rings were meshing with the pinions, and I > > > couldn't change the tooth profile to make it work better with the > software I was using. > > > > > > Todd Zuercher > > > P. Graham Dunn Inc. > > > 630 Henry Street > > > Dalton, Ohio 44618 > > > Phone: (330)828-2105ext. 2031 > > > > > > -----Original Message----- > > > From: andy pugh <bodge...@gmail.com> > > > Sent: Friday, December 17, 2021 10:43 AM > > > To: Enhanced Machine Controller (EMC) <emc-users@lists.sourceforge.net > > > > > Subject: Re: [Emc-users] Harmonic Drive > > > > > > [EXTERNAL EMAIL] Be sure links are safe. > > > > > > On Fri, 17 Dec 2021 at 15:27, Todd Zuercher <to...@pgrahamdunn.com> > wrote: > > > > > > > > Andy, Initially I thought what you are saying about the pitch > diameters needing to be the same was true. And that would be the > > > case if all the pinions had the same tooth count and size. But When I > was modeling it I found that if all of the module was the same > > > for all the gears, and adding one tooth to the output set, and the > output pinions, their pitch diameters still meshed perfectly. > > > > > > I think that whilst that will work in theory, getting it assembled > right would be a problem. > > > > > > With two ring gears with the same PCD but +1 teeth on one gear you can > have pinion pairs with equal teeth and a fixed phase > > offset. > > > These can be assembled in any rotational orientation (as long as they > are in the right place relative to each other) > > > > > > Also, with such an arrangement you can drive the pinions with a small > sun gear, for a second level of reduction. You just have to > > > make sure that the sun gear toothcount is divisible by the number of > plantets, and also that you drive the unshifted half of each > > > pinion (I think) > > > > > > > > > -- > > > atp > > > "A motorcycle is a bicycle with a pandemonium attachment and is > designed for the especial use of mechanical geniuses, daredevils > > > and lunatics." > > > - George Fitch, Atlanta Constitution Newspaper, 1912 > > > > > > > > > _______________________________________________ > > > Emc-users mailing list > > > Emc-users@lists.sourceforge.net > > > > https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.sourceforge.net%2Flists%2Flistinfo%2Femc- > > > > > users&data=04%7C01%7Ctoddz%40pgrahamdunn.com > %7C4842da1f9f934e91441e08d9c1741eef%7C5758544c573f47cebee96 > > > > > > c3e0806fb43%7C0%7C0%7C637753527048039153%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJB > > > > > > TiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=jxrNeQMSLeIFw8UIaEbmsfbb61M1abPjoVKFmwCIRP8%3D&reserved=0 > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
