All the spheres revolve about the sun as their mid-point
September 4, 2013 1:25 PM Subscribe
Ken Condal built an orrery (a mechanical model of the solar system - wikipedia), milling the parts himself using CNC machining. Among the videos are those of the orrery in operation and a time lapse of the construction process.
"Revolve around the sun"? Look, I know you're not supposed to expect the Spanish Inquisition, but let's just say the startled gasps are going to be a little forced this time.
posted by yoink at 1:33 PM on September 4, 2013 [1 favorite]
posted by yoink at 1:33 PM on September 4, 2013 [1 favorite]
i love orreries. I love them so hard. I want one. This is a great find, thanks for posting.
posted by rebent at 1:38 PM on September 4, 2013 [1 favorite]
posted by rebent at 1:38 PM on September 4, 2013 [1 favorite]
Count me among the orrery-lovers. But I, for one, would love to see an orrery built on the Ptolemaic system. Geared epicycles for retrograde motion would be so steampunk.
posted by ariel_caliban at 1:52 PM on September 4, 2013 [4 favorites]
posted by ariel_caliban at 1:52 PM on September 4, 2013 [4 favorites]
Mr. Condal really knows what he's doing and has been eminently supportive to newb machinists on various email lists.
...note that the Gearotic project file is posted on the website, so you can get a better view of the mechanism. I'm considering trying to put together a 3D-printed version, since I'm a manual machinist, kinda suck, and could not possibly build the dang thing out of metal myself. However, with the project file in hand I can (I think) establish the layout and rebuild it to a smaller scale suitable for FDM.
posted by aramaic at 1:53 PM on September 4, 2013
...note that the Gearotic project file is posted on the website, so you can get a better view of the mechanism. I'm considering trying to put together a 3D-printed version, since I'm a manual machinist, kinda suck, and could not possibly build the dang thing out of metal myself. However, with the project file in hand I can (I think) establish the layout and rebuild it to a smaller scale suitable for FDM.
posted by aramaic at 1:53 PM on September 4, 2013
That's a nice orrery, and Imma let you finish, but Aughra had the greatest orrery of all time!
posted by Rock Steady at 2:00 PM on September 4, 2013 [2 favorites]
posted by Rock Steady at 2:00 PM on September 4, 2013 [2 favorites]
That construction video was some serious How It's Made porn.
posted by chemoboy at 2:15 PM on September 4, 2013 [2 favorites]
posted by chemoboy at 2:15 PM on September 4, 2013 [2 favorites]
Aaaaaaaaaaaah, me want! Want!
posted by jeffkramer at 2:21 PM on September 4, 2013
posted by jeffkramer at 2:21 PM on September 4, 2013
Beautiful. I'm really loving the number of cool projects that are coming out of the world of relatively-inexpensive home-shop CNC machines.
Seems like there's a fair amount of slop in the gears, though... hard to tell why. But as he's turning the input crank in the video there's a pretty jerky motion in one of the main gears.
I wonder if that's a side-effect of how the gears were made, and is just the best you can do on a CNC vertical mill? Commercially, most gears are cut on a hobbing machine, which is a specialized tool that turns both the workpiece and the cutter simultaneously at different (but closely matched) speeds. The cutter cuts multiple teeth at the same time. It's quite accurate, as long as you prevent any slippage between the drive that's turning the blank and the cutter. Here's a video of a small one.
But I've never really understood the advantage of the hobbing machine vs. a mill with an indexing head, at least for cutting spur gears. I assume that there is one, or else the hobbing machines wouldn't exist, and they have been around for a while ... IIRC there is a (nonfunctional) one at the Saugus Iron Works, dating from when such a machine would have represented a huge capital expense.
I've always thought gear hobbing machines were particularly neat as they are (supposedly) one of those machines, along with lathes, that can be used to improve themselves over time. E.g. if you build a hobbing machine using hand-cut gears, it can then be used to make gears more accurate than the ones it has in it, which can then be inserted to make the machine better. I think this is due to the multiple cutting passes smoothing/averaging out problems caused by the machine's drivetrain.
posted by Kadin2048 at 2:23 PM on September 4, 2013 [5 favorites]
Seems like there's a fair amount of slop in the gears, though... hard to tell why. But as he's turning the input crank in the video there's a pretty jerky motion in one of the main gears.
I wonder if that's a side-effect of how the gears were made, and is just the best you can do on a CNC vertical mill? Commercially, most gears are cut on a hobbing machine, which is a specialized tool that turns both the workpiece and the cutter simultaneously at different (but closely matched) speeds. The cutter cuts multiple teeth at the same time. It's quite accurate, as long as you prevent any slippage between the drive that's turning the blank and the cutter. Here's a video of a small one.
But I've never really understood the advantage of the hobbing machine vs. a mill with an indexing head, at least for cutting spur gears. I assume that there is one, or else the hobbing machines wouldn't exist, and they have been around for a while ... IIRC there is a (nonfunctional) one at the Saugus Iron Works, dating from when such a machine would have represented a huge capital expense.
I've always thought gear hobbing machines were particularly neat as they are (supposedly) one of those machines, along with lathes, that can be used to improve themselves over time. E.g. if you build a hobbing machine using hand-cut gears, it can then be used to make gears more accurate than the ones it has in it, which can then be inserted to make the machine better. I think this is due to the multiple cutting passes smoothing/averaging out problems caused by the machine's drivetrain.
posted by Kadin2048 at 2:23 PM on September 4, 2013 [5 favorites]
Totally kick ass, but, I have to ask. Where are Uranus and Neptune?
posted by InsertNiftyNameHere at 2:23 PM on September 4, 2013 [1 favorite]
posted by InsertNiftyNameHere at 2:23 PM on September 4, 2013 [1 favorite]
You need a mirror and a flashlight to see Uranus.
posted by backseatpilot at 2:50 PM on September 4, 2013 [3 favorites]
posted by backseatpilot at 2:50 PM on September 4, 2013 [3 favorites]
Full marks, but what I really want is the build-it-yourself Antikythera mechanism
posted by IndigoJones at 2:55 PM on September 4, 2013 [1 favorite]
posted by IndigoJones at 2:55 PM on September 4, 2013 [1 favorite]
Does anyone know what the fixture is that he used on the lathe to turn those spheres?
posted by This_Will_Be_Good at 2:55 PM on September 4, 2013
posted by This_Will_Be_Good at 2:55 PM on September 4, 2013
this is awesome. I am new to cnc....does it say anywhere what machine he is using? and is anyone else surprised that this is not metric? I am used to tolerances this small but have a hard time thinking in thousandths not microns.
posted by OHenryPacey at 3:06 PM on September 4, 2013
posted by OHenryPacey at 3:06 PM on September 4, 2013
"Orrery" is a fun word to imagine a labrador retriever trying to say, but getting tripped up over all the r's. ORRORRORRERRRY
posted by radwolf76 at 3:16 PM on September 4, 2013 [8 favorites]
posted by radwolf76 at 3:16 PM on September 4, 2013 [8 favorites]
I want to see the machining AND some plans so I can build my own. (Manually, since I use computers enough at work.)
posted by DU at 3:32 PM on September 4, 2013
posted by DU at 3:32 PM on September 4, 2013
I love photographs of orreries but that may be the first time I've seen one in motion (short of the one that Angelina Jolie destroyed in the second Tomb Raider movie, which hardly counts).
posted by immlass at 3:35 PM on September 4, 2013
posted by immlass at 3:35 PM on September 4, 2013
I'm considering trying to put together a 3D-printed version, since I'm a manual machinist, kinda suck, and could not possibly build the dang thing out of metal myself.
I think the only thing remotely difficult in there were the gears. And if you have a dividing head (I don't) and have or can make gear cutters (I don't and haven't) that's pretty easy too.
posted by DU at 3:43 PM on September 4, 2013
I think the only thing remotely difficult in there were the gears. And if you have a dividing head (I don't) and have or can make gear cutters (I don't and haven't) that's pretty easy too.
posted by DU at 3:43 PM on September 4, 2013
IndigoJones: Full marks, but what I really want is the build-it-yourself Antikythera mechanism
Why not just build your own out of lego? It's been done.
posted by justsomebodythatyouusedtoknow at 4:30 PM on September 4, 2013
Why not just build your own out of lego? It's been done.
posted by justsomebodythatyouusedtoknow at 4:30 PM on September 4, 2013
Does anyone know what the fixture is that he used on the lathe to turn those spheres?
It's a Sherline accessory.
the only thing remotely difficult in there were the gears.
...well, yes. If you're a manual machinist, the tedium required to cut gears is spectacular. A 22-tooth, 32dp, 20deg PA gear takes me like 20 minutes. This ... thing ... would probably kill me in increments.
posted by aramaic at 5:27 PM on September 4, 2013
It's a Sherline accessory.
the only thing remotely difficult in there were the gears.
...well, yes. If you're a manual machinist, the tedium required to cut gears is spectacular. A 22-tooth, 32dp, 20deg PA gear takes me like 20 minutes. This ... thing ... would probably kill me in increments.
posted by aramaic at 5:27 PM on September 4, 2013
Yeah, I killed my neck making index marks on my homemade tailstock dial. And the tenseness as you get close to the end would make it worse. But people DO do it.
posted by DU at 5:31 PM on September 4, 2013
posted by DU at 5:31 PM on September 4, 2013
the tenseness as you get close to the end would make it worse
Oh god, I get tense just thinking about it....
posted by aramaic at 5:34 PM on September 4, 2013
Oh god, I get tense just thinking about it....
posted by aramaic at 5:34 PM on September 4, 2013
Seems like there's a fair amount of slop in the gears, though... hard to tell why. But as he's turning the input crank in the video there's a pretty jerky motion in one of the main gears.
I wonder if that's a side-effect of how the gears were made, and is just the best you can do on a CNC vertical mill?
I noticed that the calendar gear wobbles back and forth as he turns the crank. This is almost certainly due to poorly designed gear teeth. I watched the gear cutting video, the guy's description of his use of the CNC app Gearotic Motion does not impress me with his knowledge of gear design. He says his gear design "uses subroutines and variables and stuff." Right.
I looked at the orrery video in 720p, here's a screen cap. It appears that the orrery uses cycloidal gears. So I looked at the Gearotic Motion demo videos. Here's a screencap from their demo showing "cycloidic [sic] teeth." The screencast specifically says not to use advanced parameters in cycloidal teeth unless you're a gear expert. The orrery guy is not. The teeth look too straight and too deep, which can cause the gear faces to make contact incorrectly, or even drive a gear back and forth instead of a continuous forward motion.
But the wobble seems most closely associated with the pin gear driving the Moon around the Earth. I don't think you can drive a pin gear smoothly with a cycloidal gear, it has to be involute, and certainly the teeth can't be so deep as seen on the calendar gear. I suspect the improper motion of the pin gear is pushing backwards periodically into the drive mechanism.
If you want to understand the design of gear teeth, I suggest consulting the book Principles of Mechanism by Robert Willis, Cambridge University Press, 1840. I have a copy and have discussed it on MeFi several times. Here is a Google Books scan of the book. I particularly recommend starting on page 73, the chapter entitled "On The Teeth Of Wheels."
Judging by some of Willis' calculations, it appears that the fundamental problem here is designing all the gear ratios and tooth face geometries to harmonize across the entire series of multiple gears. This is the watchmaker's art. But the watchmakers have it easy. They have wider tolerances with an escapement mechanism, it moves discontinuously, once per second. Driving multiple gears with different ratios so they move smoothly and continuously is much trickier. And of course there are more fundamental design problems with this orrery, the annular gear is labeled in months rather than the zodiac.
posted by charlie don't surf at 7:15 PM on September 4, 2013 [6 favorites]
I wonder if that's a side-effect of how the gears were made, and is just the best you can do on a CNC vertical mill?
I noticed that the calendar gear wobbles back and forth as he turns the crank. This is almost certainly due to poorly designed gear teeth. I watched the gear cutting video, the guy's description of his use of the CNC app Gearotic Motion does not impress me with his knowledge of gear design. He says his gear design "uses subroutines and variables and stuff." Right.
I looked at the orrery video in 720p, here's a screen cap. It appears that the orrery uses cycloidal gears. So I looked at the Gearotic Motion demo videos. Here's a screencap from their demo showing "cycloidic [sic] teeth." The screencast specifically says not to use advanced parameters in cycloidal teeth unless you're a gear expert. The orrery guy is not. The teeth look too straight and too deep, which can cause the gear faces to make contact incorrectly, or even drive a gear back and forth instead of a continuous forward motion.
But the wobble seems most closely associated with the pin gear driving the Moon around the Earth. I don't think you can drive a pin gear smoothly with a cycloidal gear, it has to be involute, and certainly the teeth can't be so deep as seen on the calendar gear. I suspect the improper motion of the pin gear is pushing backwards periodically into the drive mechanism.
If you want to understand the design of gear teeth, I suggest consulting the book Principles of Mechanism by Robert Willis, Cambridge University Press, 1840. I have a copy and have discussed it on MeFi several times. Here is a Google Books scan of the book. I particularly recommend starting on page 73, the chapter entitled "On The Teeth Of Wheels."
Judging by some of Willis' calculations, it appears that the fundamental problem here is designing all the gear ratios and tooth face geometries to harmonize across the entire series of multiple gears. This is the watchmaker's art. But the watchmakers have it easy. They have wider tolerances with an escapement mechanism, it moves discontinuously, once per second. Driving multiple gears with different ratios so they move smoothly and continuously is much trickier. And of course there are more fundamental design problems with this orrery, the annular gear is labeled in months rather than the zodiac.
posted by charlie don't surf at 7:15 PM on September 4, 2013 [6 favorites]
Hi Everyone. I just wanted to check in and thank you all for the encouraging comments regarding my Orrery.
There was a question regarding the meshing of the gears and whether that was a side effect of using a vertical mill. I can assure you, the individual gears mesh perfectly. What you're seeing in the video is the result of two things. First, in a gear train of 30 gears, all supported on a small column in the center of the Orrery, there is going to be some backlash. Second, and probably the biggest problem, is that the large blue gear at the top is also supporting the Earth, Moon and the cage gear that drives the Moon. All of that weight causes the large blue gear to wobble a little bit.
The other comment was a request to see more of the build process. My website has many hours of videos where I detail the entire build.
Thanks again,
Ken
posted by Zeamon at 7:18 PM on September 4, 2013 [17 favorites]
There was a question regarding the meshing of the gears and whether that was a side effect of using a vertical mill. I can assure you, the individual gears mesh perfectly. What you're seeing in the video is the result of two things. First, in a gear train of 30 gears, all supported on a small column in the center of the Orrery, there is going to be some backlash. Second, and probably the biggest problem, is that the large blue gear at the top is also supporting the Earth, Moon and the cage gear that drives the Moon. All of that weight causes the large blue gear to wobble a little bit.
The other comment was a request to see more of the build process. My website has many hours of videos where I detail the entire build.
Thanks again,
Ken
posted by Zeamon at 7:18 PM on September 4, 2013 [17 favorites]
Ah, perhaps it was premature to judge the accuracy of the gear meshing from the video. But it appears that yes, the lunar gear is the problem. It always is. These little cycles are always a pain in the ass. Ptolemy would agree.
My junior high school had a huge antique orrery that I played with endlessly. It had a radius of about 2 feet and had a chain drive. I don't even want to think about that design, but Willis' book covers that too.
posted by charlie don't surf at 7:32 PM on September 4, 2013 [1 favorite]
My junior high school had a huge antique orrery that I played with endlessly. It had a radius of about 2 feet and had a chain drive. I don't even want to think about that design, but Willis' book covers that too.
posted by charlie don't surf at 7:32 PM on September 4, 2013 [1 favorite]
Charlie, I believe you misunderstood my explanation of how I made the gears. Gearotic Motion was only used as a proof of concept to ensure that all of the gear ratios were correct. I did not use Gearotic Motion to generate the CNC code, instead I hand coded it using variables and subroutines so that all of the gears could be made with a single routine, simply by changing a variable.
The gears were cut with a high quality horological cutter that I purchased and they are all cut to the proper depth.
As far as driving a cage gear with a cycloidal gear, this is indeed possible and not uncommon. I consulted with an expert clock maker who showed me how to do it.
Thank you for the links on gear making, I'll check them out.
posted by Zeamon at 7:54 PM on September 4, 2013
The gears were cut with a high quality horological cutter that I purchased and they are all cut to the proper depth.
As far as driving a cage gear with a cycloidal gear, this is indeed possible and not uncommon. I consulted with an expert clock maker who showed me how to do it.
Thank you for the links on gear making, I'll check them out.
posted by Zeamon at 7:54 PM on September 4, 2013
I think we were writing those messages at the same time, so neither of us had seen the other, and it looks like we were criticizing each other's comments. And that was not the case.
I'm not a machinist, but gears are one of my pet interests, ever since my Grandfather gave me his old copy of Principles of Mechanism. That book is one of my most prized possessions, and it turned out to be very useful. I got fed up with seeing improperly designed gears as a cliche in computer graphics, and made sure my CG gears always worked right.
Anyway, you will surely forgive me for any criticisms of your orrery, once you read Principles of Mechanism. In some previous discussions, we lamented that this sort of knowledge is not widely known today, when machinists were fabricating systems to run whole factories using gears and linkages back in the 1840s. So I leave this fascinating book in your hands.
posted by charlie don't surf at 8:16 PM on September 4, 2013 [3 favorites]
I'm not a machinist, but gears are one of my pet interests, ever since my Grandfather gave me his old copy of Principles of Mechanism. That book is one of my most prized possessions, and it turned out to be very useful. I got fed up with seeing improperly designed gears as a cliche in computer graphics, and made sure my CG gears always worked right.
Anyway, you will surely forgive me for any criticisms of your orrery, once you read Principles of Mechanism. In some previous discussions, we lamented that this sort of knowledge is not widely known today, when machinists were fabricating systems to run whole factories using gears and linkages back in the 1840s. So I leave this fascinating book in your hands.
posted by charlie don't surf at 8:16 PM on September 4, 2013 [3 favorites]
Charlie, I didn't take your comments as a criticism and I was only trying to clarify some of the points you brought up. I understand and appreciate your passion for doing things right.
I look forward to reading Principles of Mechanism.
posted by Zeamon at 8:29 PM on September 4, 2013 [2 favorites]
I look forward to reading Principles of Mechanism.
posted by Zeamon at 8:29 PM on September 4, 2013 [2 favorites]
Hi Ken, thanks for dropping by.
Consider me a fanboy. Don't worry, nothing creepy, just complete envy of a man who can make his Sherline do things mine can only dream of. :-)
posted by Tell Me No Lies at 9:54 PM on September 4, 2013
Consider me a fanboy. Don't worry, nothing creepy, just complete envy of a man who can make his Sherline do things mine can only dream of. :-)
posted by Tell Me No Lies at 9:54 PM on September 4, 2013
Count me among the orrery lovers as well. I even went so far as to spend a month Modeling and animating one in 3D. Alas, the gears are not "accurate," they're just for show, though when animated, they move and interact convincingly. All the planets move correctly as well. Unfortunately, it takes about 16 hours to render a single frame, so I never got around to creating a high quality video clip of it in motion.
posted by ShutterBun at 11:47 PM on September 4, 2013
posted by ShutterBun at 11:47 PM on September 4, 2013
That's a nice orrery, and Imma let you finish, but Aughra yt had the greatest orrery of all time!
I'm currently trying to build a reasonable replica of Aughra's orrery out of LEGO, and man is it a pain in the ass. Having studied the video repeatedly and seen how the upper portion is tilted and rotates, the original must have mostly been built out of styrofoam or hollow plastic in order to work.
posted by AlonzoMosleyFBI at 5:20 AM on September 5, 2013 [1 favorite]
I'm currently trying to build a reasonable replica of Aughra's orrery out of LEGO, and man is it a pain in the ass. Having studied the video repeatedly and seen how the upper portion is tilted and rotates, the original must have mostly been built out of styrofoam or hollow plastic in order to work.
posted by AlonzoMosleyFBI at 5:20 AM on September 5, 2013 [1 favorite]
AlonzoMosleyFBI: I'm currently trying to build a reasonable replica of Aughra's orrery out of LEGO, and man is it a pain in the ass.
That sounds amazing! I would love to see photos.
posted by Rock Steady at 5:44 AM on September 5, 2013
That sounds amazing! I would love to see photos.
posted by Rock Steady at 5:44 AM on September 5, 2013
Thanks, Rock Steady. Providing I ever finish the thing, I'll send you a link to the pics I post of Flickr.
posted by AlonzoMosleyFBI at 6:56 AM on September 5, 2013
posted by AlonzoMosleyFBI at 6:56 AM on September 5, 2013
I didn't even realize it was made on a Sherline. I've had my finger poised over my mouse which was poised over the "Buy" button on Sherline's website more times than I can count... but haven't actually pulled the trigger. One of these days, though. Such neat little machines.
Also, thanks to Zeamon for dropping by and answering questions.
posted by Kadin2048 at 12:56 PM on September 5, 2013
Also, thanks to Zeamon for dropping by and answering questions.
posted by Kadin2048 at 12:56 PM on September 5, 2013
Why not just build your own out of lego?
Nice! But I'm more a wood and brass man than a plastic guy. Still....
posted by IndigoJones at 3:05 PM on September 5, 2013
Nice! But I'm more a wood and brass man than a plastic guy. Still....
posted by IndigoJones at 3:05 PM on September 5, 2013
Count me among the orrery lovers as well. I even went so far as to spend a month Modeling and animating one in 3D. Alas, the gears are not "accurate," they're just for show, though when animated, they move and interact convincingly. All the planets move correctly as well.
Orrerries are nice toys but if you're going to be serious, it should accurately represent the live positions of the planets. This is impossible with circular gears, unless you use the Ptolemaic hack of the epicycle and even then, it's inaccurate and has to be manually adjusted when it starts to lag behind the positions of the planets in their true elliptical orbit. You could use non-circular gears to simulate elliptical orbits. The design of such a gear system is left as an exercise for the reader.
I did find one Java applet with a live heliocentric chart, essentially a 2D orrery. Of course geocentric models are commonplace. Full 3D geocentric models like Stellarium are the ultimate evolution of this model.
Certainly Mr. Condal has considered the history of the Lunarium, and antique models might help show how to rectify his balky lunar pin gear. Here is a general history of orreries, armilary spheres, and astrolabes. There is a particularly interesting photo of a lunarium arm from an antique orrery, it shows the tllt of the moon's orbit relative to the ecliptic, and demonstrates the lunar nodes. There is also a photo of a telurium, which is a simple orrery consisting solely of the Earth and Moon.
BTW, I have recently been needling some astrologers who want to include Centaurs like Chiron and Trans-Neptunian Objects into the heliocentric model. I tell them, I think it's foolish to start scraping the Oort Cloud for new objects, when nobody has yet accounted for influences from the orbits of moons around planets like Mars and Saturn that have been known for hundreds of years. I was surprised when one very clever person finally suggested you could calculate any planet's ascending and descending lunar nodes for each moon, and lunar-to-lunar aspects for planets with more than one moon. She suggested the example of of Deimos and Phobos from a Mars-centric position. And damn if the next week, photographs of a Martian solar eclipse were published, taken from Curiosity rover, just as Phobos passed in front of the sun, at the exact position of a lunar node. It suddenly occurred to me, there must be detailed ephemerides of Deimos and Phobos. There must also be detailed ephemerides of every extraterrestrial moon in the solar system. With accurate ephemerides of the planets, and their moons, the construction of extraterrestrial planet-centric digital astrology software is trivial. The construction of such software is left as an exercise for the reader.
(although seriously, if you could write this software, I know people who would pay serious money for it)
posted by charlie don't surf at 6:40 PM on September 5, 2013 [2 favorites]
Orrerries are nice toys but if you're going to be serious, it should accurately represent the live positions of the planets. This is impossible with circular gears, unless you use the Ptolemaic hack of the epicycle and even then, it's inaccurate and has to be manually adjusted when it starts to lag behind the positions of the planets in their true elliptical orbit. You could use non-circular gears to simulate elliptical orbits. The design of such a gear system is left as an exercise for the reader.
I did find one Java applet with a live heliocentric chart, essentially a 2D orrery. Of course geocentric models are commonplace. Full 3D geocentric models like Stellarium are the ultimate evolution of this model.
Certainly Mr. Condal has considered the history of the Lunarium, and antique models might help show how to rectify his balky lunar pin gear. Here is a general history of orreries, armilary spheres, and astrolabes. There is a particularly interesting photo of a lunarium arm from an antique orrery, it shows the tllt of the moon's orbit relative to the ecliptic, and demonstrates the lunar nodes. There is also a photo of a telurium, which is a simple orrery consisting solely of the Earth and Moon.
BTW, I have recently been needling some astrologers who want to include Centaurs like Chiron and Trans-Neptunian Objects into the heliocentric model. I tell them, I think it's foolish to start scraping the Oort Cloud for new objects, when nobody has yet accounted for influences from the orbits of moons around planets like Mars and Saturn that have been known for hundreds of years. I was surprised when one very clever person finally suggested you could calculate any planet's ascending and descending lunar nodes for each moon, and lunar-to-lunar aspects for planets with more than one moon. She suggested the example of of Deimos and Phobos from a Mars-centric position. And damn if the next week, photographs of a Martian solar eclipse were published, taken from Curiosity rover, just as Phobos passed in front of the sun, at the exact position of a lunar node. It suddenly occurred to me, there must be detailed ephemerides of Deimos and Phobos. There must also be detailed ephemerides of every extraterrestrial moon in the solar system. With accurate ephemerides of the planets, and their moons, the construction of extraterrestrial planet-centric digital astrology software is trivial. The construction of such software is left as an exercise for the reader.
(although seriously, if you could write this software, I know people who would pay serious money for it)
posted by charlie don't surf at 6:40 PM on September 5, 2013 [2 favorites]
Upon further review, I'm gonna go ahead and downgrade myself to "people who just think orreries are kinda neat."
posted by ShutterBun at 2:53 AM on September 6, 2013 [8 favorites]
posted by ShutterBun at 2:53 AM on September 6, 2013 [8 favorites]
"This is impossible with circular gears, unless you use the Ptolemaic hack of the epicycle..."
Are you sure you don't mean the equant and not the epicycle? I can't see any reason why there would be a problem with epicycles, those are regular, circular motions along the path of another regular, circular motion. However, the primary circle is the deferent, and IIRC most or all of the deferents are not centered on the Earth, but are slightly eccentric, including the Sun's, of course. But I don't see how that would be a problem, either.
But the equant is a problem because it's a motion described as a regular, circular motion that's centered elsewhere than the actual center of motion — that is to say, it's the center of a circle of apparent regular motion, with the actual path of motion a circle that's centered independently.
I found that this was easiest to conceptualize as a motor driving a rod that is an axle to a sphere which rotates around the axle but is free to move lengthwise along it, inward and outward. Then imagine that the sphere rolls along a pair of rails that form a circle. You can shift that circle eccentric to the motor so that the sphere moves away from the motor and then back toward it as it travels along its circular path; and as it does so its rate of angular motion will increase and decrease along that circular path formed by the rails which is eccentric to the motor. But of course its rate of angular motion about the motor will be regular. So in ptolemaic terms, the motor is the center of the equant, and the equant is the imaginary circle centered on that motor, while the deferent is the center of the those rails, the circular path upon which that sphere actually moves.
And then of course ptolemy would have the "star" traveling not on the deferent, but on another circle centered on that deferent, which would be an epicycle. And so on with further elaborations.
I don't consider the epicycles a "hack", they seem to me to be a reasonable mechanism by which the motions can be understood as regular and circular. I actually think the eccentric deferent is more problematic right from the beginning when it appears for the Sun, given that the whole project is built around the assumption that these motions are ultimately centered around the Earth. Even so, in my opinion the violation of parsimony that people typically attribute to epicycles is much better applied to the equant. Without the equant, I think this is a conception of the motions of the heavens that is, in relative terms, fairly comprehensible mechanically. But the equant is a complication where I think it's natural to incredulously ask why in the world would it be doing that?
Kevin Brown's discussion of ptolemaic astronomy is more interesting than Wikipedia's.
posted by Ivan Fyodorovich at 9:57 AM on September 7, 2013
Are you sure you don't mean the equant and not the epicycle? I can't see any reason why there would be a problem with epicycles, those are regular, circular motions along the path of another regular, circular motion. However, the primary circle is the deferent, and IIRC most or all of the deferents are not centered on the Earth, but are slightly eccentric, including the Sun's, of course. But I don't see how that would be a problem, either.
But the equant is a problem because it's a motion described as a regular, circular motion that's centered elsewhere than the actual center of motion — that is to say, it's the center of a circle of apparent regular motion, with the actual path of motion a circle that's centered independently.
I found that this was easiest to conceptualize as a motor driving a rod that is an axle to a sphere which rotates around the axle but is free to move lengthwise along it, inward and outward. Then imagine that the sphere rolls along a pair of rails that form a circle. You can shift that circle eccentric to the motor so that the sphere moves away from the motor and then back toward it as it travels along its circular path; and as it does so its rate of angular motion will increase and decrease along that circular path formed by the rails which is eccentric to the motor. But of course its rate of angular motion about the motor will be regular. So in ptolemaic terms, the motor is the center of the equant, and the equant is the imaginary circle centered on that motor, while the deferent is the center of the those rails, the circular path upon which that sphere actually moves.
And then of course ptolemy would have the "star" traveling not on the deferent, but on another circle centered on that deferent, which would be an epicycle. And so on with further elaborations.
I don't consider the epicycles a "hack", they seem to me to be a reasonable mechanism by which the motions can be understood as regular and circular. I actually think the eccentric deferent is more problematic right from the beginning when it appears for the Sun, given that the whole project is built around the assumption that these motions are ultimately centered around the Earth. Even so, in my opinion the violation of parsimony that people typically attribute to epicycles is much better applied to the equant. Without the equant, I think this is a conception of the motions of the heavens that is, in relative terms, fairly comprehensible mechanically. But the equant is a complication where I think it's natural to incredulously ask why in the world would it be doing that?
Kevin Brown's discussion of ptolemaic astronomy is more interesting than Wikipedia's.
posted by Ivan Fyodorovich at 9:57 AM on September 7, 2013
I think I had something very like a sexual experience just now watching the construction process video.
posted by Ivan Fyodorovich at 10:19 AM on September 7, 2013 [2 favorites]
posted by Ivan Fyodorovich at 10:19 AM on September 7, 2013 [2 favorites]
Zeamon: "Hi Everyone. I just wanted to check in and thank you all for the encouraging comments regarding my Orrery.
There was a question regarding the meshing of the gears and whether that was a side effect of using a vertical mill. I can assure you, the individual gears mesh perfectly. What you're seeing in the video is the result of two things. First, in a gear train of 30 gears, all supported on a small column in the center of the Orrery, there is going to be some backlash. Second, and probably the biggest problem, is that the large blue gear at the top is also supporting the Earth, Moon and the cage gear that drives the Moon. All of that weight causes the large blue gear to wobble a little bit.
The other comment was a request to see more of the build process. My website has many hours of videos where I detail the entire build.
Thanks again,
Ken"
Lovely work and all, but what the hell are all the globular things? I can appreciate a serious DIY project as well as the next man, but I really must object to your obvious anti-flat agenda. Might I suggest NOT listing this as an orrery, but a motion art project? We need to keep it scientifically accurate if you are calling it an orrery.
I bet you believe vaccinations are good, don't you?
Seriously. REALLY awesome. Wish I could do such things. As for the flat earth/vax thing, I keed, I keed.
posted by Samizdata at 12:10 PM on September 7, 2013
There was a question regarding the meshing of the gears and whether that was a side effect of using a vertical mill. I can assure you, the individual gears mesh perfectly. What you're seeing in the video is the result of two things. First, in a gear train of 30 gears, all supported on a small column in the center of the Orrery, there is going to be some backlash. Second, and probably the biggest problem, is that the large blue gear at the top is also supporting the Earth, Moon and the cage gear that drives the Moon. All of that weight causes the large blue gear to wobble a little bit.
The other comment was a request to see more of the build process. My website has many hours of videos where I detail the entire build.
Thanks again,
Ken"
Lovely work and all, but what the hell are all the globular things? I can appreciate a serious DIY project as well as the next man, but I really must object to your obvious anti-flat agenda. Might I suggest NOT listing this as an orrery, but a motion art project? We need to keep it scientifically accurate if you are calling it an orrery.
I bet you believe vaccinations are good, don't you?
Seriously. REALLY awesome. Wish I could do such things. As for the flat earth/vax thing, I keed, I keed.
posted by Samizdata at 12:10 PM on September 7, 2013
AlonzoMosleyFBI: "Thanks, Rock Steady. Providing I ever finish the thing, I'll send you a link to the pics I post of Flickr."
Me too? Because, I do an awesome Aughra imitation.
posted by Samizdata at 12:11 PM on September 7, 2013
Me too? Because, I do an awesome Aughra imitation.
posted by Samizdata at 12:11 PM on September 7, 2013
I'm basically dribbling from both sides of my mouth right now, unsure which link to click on next.
This is spectacularly beautiful stuff.
Thank you.
posted by motty at 6:20 PM on September 7, 2013
This is spectacularly beautiful stuff.
Thank you.
posted by motty at 6:20 PM on September 7, 2013
Thank you , Ivan, for that useful link to Ptolemaic astronomical calculations. I am in the midst of some intense calculations, and am currently going through some IAU reference materials for some of the subtler points. Dammit why does the IAU insist I have to apply Chebychev Polynomials to spherical coordinates, just to interpolate between two momentary planetary positions in the ephemeris? But despite some difficulties converting coordinate systems, I have been entirely successful in my attempts to calculate astronomical data from positions that are Mars-centric, Jupiter-Centric, and even Uranus-centric and beyond. The Ptolemaic system is amusing, but of no practical use whatsoever for these calculations. But it is far more amusing than the real calculations, no wonder people love orreries.
As far as the issues of the epicycle, perhaps I have confused the issue by describing the Lunar gear as an epicycle around the Earth's position on the annular gear. I was actually writing that while looking at Principles of Mechanism and their description of epicyclical gears, not using it in the Ptolemaic sense. I was trying to avoid complications with the equant and deferent, and yes Ptolemy realized these cycles are problematic when applied to planetary motion. It is beyond the scope of a basic orrery to perform these motions with gears, unless you intend to produce a grand Astrarium. Again Principles of Mechanism is the go-to guide, as it describes elliptical gear and linkage mechanisms to convert a driving rotary axle to complex elliptical motion in a plane. But this is not very practical.
posted by charlie don't surf at 10:42 PM on September 7, 2013
As far as the issues of the epicycle, perhaps I have confused the issue by describing the Lunar gear as an epicycle around the Earth's position on the annular gear. I was actually writing that while looking at Principles of Mechanism and their description of epicyclical gears, not using it in the Ptolemaic sense. I was trying to avoid complications with the equant and deferent, and yes Ptolemy realized these cycles are problematic when applied to planetary motion. It is beyond the scope of a basic orrery to perform these motions with gears, unless you intend to produce a grand Astrarium. Again Principles of Mechanism is the go-to guide, as it describes elliptical gear and linkage mechanisms to convert a driving rotary axle to complex elliptical motion in a plane. But this is not very practical.
posted by charlie don't surf at 10:42 PM on September 7, 2013
Me too? Because, I do an awesome Aughra imitation.
People living with glass eyes...etc.
posted by ShutterBun at 12:46 AM on September 8, 2013
People living with glass eyes...etc.
posted by ShutterBun at 12:46 AM on September 8, 2013
There was a time when I tried to write a filthy limerick about the Earl of Orrery. The best I could come up with was:
posted by Pallas Athena at 4:11 PM on September 8, 2013 [2 favorites]
The dashing, debauched Earl of OrreryPretty feeble, right? I bet you, fellow MeFites, can do better...
Lured more than one girl into whorery.
He'd invite them upstairs
And expose to their stares
His device for celestial explorery.
posted by Pallas Athena at 4:11 PM on September 8, 2013 [2 favorites]
Lord Boyle was the first Earl of Orrery
Forthwith Roger tells his life storrery:
"I wrote sev'ral plays,
Fought in wars most my days,
But in Ireland such things were quite ord'nary."
posted by ShutterBun at 2:18 AM on September 9, 2013 [1 favorite]
Forthwith Roger tells his life storrery:
"I wrote sev'ral plays,
Fought in wars most my days,
But in Ireland such things were quite ord'nary."
posted by ShutterBun at 2:18 AM on September 9, 2013 [1 favorite]
That is just fucking awesome and beautiful. Truly a masterpiece.
posted by theora55 at 11:37 AM on September 12, 2013
posted by theora55 at 11:37 AM on September 12, 2013
Thank you! Didn't really take very long either.
Oh wait, you meant the bitchin' model...
posted by ShutterBun at 9:32 PM on September 12, 2013 [2 favorites]
Oh wait, you meant the bitchin' model...
posted by ShutterBun at 9:32 PM on September 12, 2013 [2 favorites]
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