Split Ring Compound Planet Epicyclic Gear

hello so this entry is about something that I am absolutely obsessed with and fascinated by it's also extremely geeky so I wanted to talk with you today about something called the split ring compound planet epicyclic gear now it's a special arrangement of gears and what makes it so special is that this type of gear arrangement can be very flat can be powerful it can be precise it can have very low backlash and it has relatively few gears for the kinds of ratios you can get hundreds or thousands to one and most importantly for my purposes its 3d principle I want to show you what I mean by split ring meaning it uses an internal gear actually uses two of them so they're split you have one annulus a one and the second annual is a two there are planetary gears that rotate around the inside P one-type years p2 type years and then there are two suns one is attached to the motor the second one interestingly enough is attached to nothing it sits there as an idler to kind of hold the gears in place and spread them against the inner wall of the second annual Asst and the the entire second annulus rotates as the output shaft this is pretty abstract let me show you what one of these things actually looks like here I've got one I 3d printed and I have it lined up here I can hit go and it chugs right along this doesn't even have any bearings at all so it has a little bit of play a little bit of wobble I'll hit play one more time I'll show you what the coolest thing about this though is watch this I'll take I'll take the top off and open it up this particular gear arrangement actually has a ratio of 528 to one and if you look at the inside it has the output shaft has one annulus the inside has another you can you can see the teeth there and I'll hit I'll hit go again [Music] interestingly enough remember what I told you about there being an idler this is the idler it just sits there and it pushes these gears out against the inside of the inside of this one really the whole thing will work without this but play again and see there's just one little Sun gear in the middle oh here it is huh it just goes on to the motor and turns so there's the first stage if you look at the layout here what I think is so interesting is how few gears there are for that high ratio the first annua so annulus one is around the inside of this and it has in this case it has 132 teeth to it there is the little Sun gear in the middle and this one actually has 12 only 12 teeth to it and then the compound planets and these are compound planets because each of the planets has two separate sets of teeth with slightly different pitches they ride right in there I'll just put one back and it drives it around in a circle and lastly annulus number two but by the way each of these compound planets has 60 teeth on the top and 60 teeth on the bottom it doesn't have to necessarily be that but this one is just the same the bottom annulus or the output annulus is 135 teeth top one has 132 you can think of the high ratio as owing to the fact that every time one of these teeth one of these planets goes all the way around the second annulus has only advanced by a matter of three teeth so an entire revolution of a planet of an entire planet all the way around advances it by three T so I flip this back on there and I make an attempt to hold it Center it I can put this carriage on there [Music] it continues on its merry way albeit it's able to slip now because it doesn't have the other teeth kind of holding its position this is a very good demonstrator for use of of 3d printing the teeth to line up in the right place put this little one in there let's check and make sure it goes yeah and then I can put the output back on there hopefully it's central it's a reasonably well century and bring this on out so I can see what's going on yeah it's very very difficult to stop as you might imagine this is the kind of thing you could use on a telescope mount or a solar tracker or even a robot arm I mean you could imagine this being the elbow of a robot arm I put holes in this you could bolt a plate here very very strong from only a little NEMA 17 stepper motor so if you're interested in more about this check out the links I provided a link to a spreadsheet that shows you a little bit more about the rules of how to choose the teeth and the gearing the real clincher seems to be once you've worked out the teeth number and how they relate you have to size that the second set of gears so that the radius between the center of the Sun and the center of one of the planets is the same that way the planet the compound planets have the same shaft so this one and this one those line up so you end up you end up having an odd kind of partial size difference you can see the size of the the pitch is it's just slightly different in order to make this Center share an axis of rotation anyway that's a there's some geeky gear stuff for your next project the split ring compound planet epicyclic gear have fun

Channel: David Hartkop

Views: 22,458

Rating: 4.9302831 out of 5

Keywords:

Id: -VtbSvVxaFA

Length: 7min 56sec (476 seconds)

Published: Fri Mar 17 2017