The Compound Cycloidal Drive - Something Novel

hey how's it going the other day I got a comment on one of my cycloidal drive related videos and it brought up the idea of making a multi-stage like play-doh Drive that's all in one in one layer I don't know if the technical name for this is a layer but that's what I'm calling it it makes sense this is an idea that I thought about quite a while ago but I never actually tried to implement it I've designed my own take on a two-stage like little Drive and this is fundamentally different from that so it's a little bit of an interesting challenge but that comment put this idea in the forefront of my mind so I thought I'd go ahead and try and design it and I have come up with it and a very effective multistage cycloidal Drive that's all in the one layer so this is what I have designed here I think cyclo dries in general are inherently mesmerizing just the the fascinating rotation of it but this one I think is uniquely so so this is the the input shaft here it's not an eccentric variance that is the the shaft is just eccentrically located so then I can make I can just use a normal bearing which just makes the design easier if I go ahead and turn this you can see the normal cycloidal motion in the center and then you can kind of see how that translates to the same cycloidal motion on the outer ring so the inside spinning very quickly in the outside very slowly this whole thing is actually a 299 to one gear reduction the inside of it is a 13 to one and then the outside is a 23 to one but before we try to understand the entire mechanism as a whole it's important to look at the inside of it to look at the the basic version of it and try to understand it on a smaller scale so this bit here if you have any familiarity with cycler drives should not be very new to you this is pretty much just a normal cycloidal Drive except that it's not there's a fundamental twist that this has that makes this whole system possible in a normal cycle it'll drive you have an eccentric bearing that wobbles a a sick little gear and a cycloidal gear itself what does the turning the gear is then coupled to the output and then you have your reduced your reduced rotation and this though it's a little bit different so I go ahead and turn the shaft again here you'll see that it's kind of backwards so we have these four pins here that that are going up into the cycloidal gear these pins are fixed directly to the base here as you can see and then this circular base plate here is effectively just representing the frame of your motor the casing of your motor something like that it's rigidly fixed in place so we have these four pins going into our cycloidal gear what that means is that the gear itself is not allowed to rotate when I turn this the gear is not rotating anywhere it is wobbling in that circular movement that cyclic motion but it's not actually turning where you would normally have a rotating cycloidal gear and a fixed outer gear in this system you instead have a fixed though wobbling cycloidal gear and a rotating outer gear so it's like little you're effectively stays in place and then the outer black piece will turn now this in and of itself is quite an interesting thing and could be helpful for your for your robotic or gearbox needs just by itself this does a couple things where normally these cycloidal gear is wobbling in this case the the the outer gear here is not wobbling what this means is that you don't have to rectify that motion like you normally would with this like little drive instead this outer ring here is already a perfectly smooth motion with constant center point no matter what so that alone is very helpful it also means that the output is on the outside which can also be very helpful with an almost like little gear the output is kind of like a separate layer and it's often above or at the center so it's like an output shaft for me at least I always want high torque and for high torque things I don't really want a shaft I instead want arms that go out and I'll attach my thing whatever mounting points to those arms if you're rotating if your output rotating gear like this is already on the outside that makes it a lot easier it's already at a position that makes high torque applications more more easy to to attach to it the other thing this does is it actually increases the gear reduction ever so slightly right here my cycloidal drive has 12 lobes on it or 12 years effectively what this would mean a normal cycloidal system is that it would be a twelve to one reduction but with this since we're kind of flipping it inside out and doing it backwards this is actually a 13-2 want reduction because my outer gear has 13 lobes or teeth on it so when you're looking when you're doing it like this in the backwards way you look at the outsides of the inside making it 13 so it is giving you a little bit more torque than you would normally which is just an added little benefit here so this thing alone not even taking into account the entire mechanism is already pretty cool I'm sure I'm not the first one to come up with it because it's not it's not that spectacular of an idea it's not that unique or anything it's just you know flipping it inside out but it is somewhat novel and this is definitely a helpful configuration in a lot of scenarios so I'm happy with this alone I will almost certainly use this at some point for some project but if we can understand how this works we can more easily understand how the whole thing works so effectively we have an internal rotation and then our output is just on the outside of that you'll also see here that this thing is not a perfect circle it could be a perfect circle if I wanted it to be but I intentionally did not make it that way this black piece here is acting doubly as my my output gear for the inner stage and as the eccentric spacer for my second stage so I had another bearing on here which is pretty big unfortunately and then my my outer stage cycloidal gear and then finally my outer stage output my final output gear so as my interstage turns it turns this eccentric spacer which turns the the whole big bearing in an eccentric manner and then the outside is doing exactly the same thing as the inside the second stage cycloidal gear is not is not rotating it is a it is fixed in place by pins that are attached directly to the motor frame the motor casing so the output gear is not allowed to turn it all instead it's just wobbling in that circular motion just like the inner gear and it's pushing along this outer black piece which is our final output I've been thinking about this as a compounds like little gear which is quite different from a typical two-stage cycloidal gear a normal two-stage like little gear which was it kind of stacks up in layers that uses the difference between two stages and the reduction is proportional to that difference it's weird how it works and it's kind of difficult to wrap your mind around the idea here is really the same as just a compound gear set it doesn't have any weird stuff to do with the difference between ratios instead it's just you multiply them that's all so the inside I have a 13 to 1 the outside my outer psyche little gear has 22 lobes which means that my black piece here has 23 lobes making it 823 to one for the same reason that you had to do it to the inside and you can pretty clearly understand why these are just being multiplied if you were to take out all of the inside stuff here all of the the inner stage then you could see how it would just be a normal cycle it'll drive you could just have it an eccentrically spaced shaft and it would accomplish the same thing as that outer gear so all you're doing is you're kind of just replacing the shaft with another stage that then rotates the gear eccentrically this also means that you can very easily add more stages to this this could be a three or four or five or six days cycloidal drive I don't know why you'd want that but it could be and it would also be in that one layer if I modified this output gear here to be to fit a bearing eccentrically I could then have a third stage on it pretty easily all the same way designed in the same fashion I just need to add more so now let's talk a little bit about the problems with this design one of them is is vibration is that vibration could be a pretty big issue here the vibration is always a problem with cycloidal drives and in if you just have a single stage like little Drive just normal you can usually without too much difficulty add a counterweight to the input shaft and that'll balance it out so then you you negate the vibration either that or you can just add another stage which kind of defeats the purpose in this scenario at least so with this at least with the inner gear you could do the same thing you could add a counter way to the to the input shaft that would offset the mass and then you would negate the vibration there but then there's also the outside which becomes more difficult you would effectively need to attach a counter mass to this black piece to this this first stage output here and there's not a lot of room for it I mean we're kind of like squished up against the bearing here if it was bigger then you could add more room but it's not it's not as simple as it could be for the first stage depending on your application though it could be that this output is rotating so much slower that vibrations is not an issue I mean vibration will almost certainly be an issue with this with the center one again that can potentially be adjusted for but the second one's gonna be already going so much slower it might not be something something to write home about another potential issue for this is just supporting the entire mechanism so you could kind of see that there's a internal ring here so this black piece this bearing and this outer cycloidal gear they're all connected or they're like pressed put together something like that and they're not rigidly fixed to anything they're kind of just floating there or not really floating but you get what I mean this could be solved pretty easily if you give it more space if you're willing to make the whole year bigger you could add bearings into here to support it and rigidly hold everything in place effectively just giving it more eccentric bearings just on these on these shafts that hold it in place you could do that it would but it would take more space which is a downside then again it might just hold itself in place depending if you if you design it correctly so it could be a non-issue but the biggest problem with this design the reason that's that I'm not totally happy with it and the reason that I will not be using this for for a project that I have plans for is is the bearing is that this design requires that each step has one of these big big bearings in between it as an inner intermediary this bearing is absolutely necessary if you didn't have it you would just have a circle of plastic turning inside of another circle of plastic or metal or whatever which is not ideal at all not to mention that if you did that they wouldn't be supported and they could just fall apart which is not great but anyways the reason that I don't want to have to have these big bearings is for size this design is as small as I could possibly make it it's the the minimum dimensions this bearing you see at the center is five millimeters diameter and has a two millimeter bore which is pretty much as small as you can get it's as small as is commercially available you can get three millimeter diameter bearings with one millimeter bores there is nothing smaller than that readily available so you could make this a little bit smaller but that comes with other constraints so not only does does the requirement of these big bearings mean that it just takes up more space than it should these these bearings are also hard to source it's hard to find these really large outer diameter bearings that are that are also really thin and they also become much thicker the bigger you get so they're effectively taller which means that your actual gears could be only a couple millimeters tall and that's fine but then the bearing is like seven millimeters thick so it's just it just Dwarfs everything else so if you could make custom bearings if you had the capacity to do that you could really knock this design that of the park and make it something really special but I can't do that and most people can't so that's in my opinion that's the biggest limitation so this is like I said this is as small as I could make it and it's still around 40 millimeters in Dianna's 38 millimeters diameter and it's effectively the absolute minimum size so I'm not super happy about that I do have plans to make a brushless micro servo and that's not gonna work with this because it's gonna be too big even even using these 1.5 millimeter shafts and that sort of thing it's just not gonna work but nonetheless this was an enjoyable thought experiment if nothing else and it looks really cool it's a it's a beautiful motion I'm definitely a lot happier with this then I was with my two-stage cycloidal drive I'm at the end of the day I really like this it looks really cool too if it weren't for the fact that it requires these hard to source really big oversized bearings I would I would be very willing to work out the other problems with it and make it a viable solution and use it in projects but I just can't find a way around these really big bearings without a fundamentally different design but hopefully you got something out of this if nothing else if even if the the two-stage doesn't work for you just the single stage inside out sort of cycloidal drive that in and of itself is a very useful thing it's just another tool in your toolbox if you would like to support me in my projects and get access to the CAD files that I showed you in this video you can find those on my patreon I would love to hear anyone's thoughts on this design ways to improve it or a different different use cases for it I am curious if anyone has any ideas on how to get around the my problem with the bearings the bearings being too big and hard to source that would be wonderful if someone can figure that out that just be great but anyways that is all I have for you today so bye

Channel: Levi Janssen

Views: 24,824

Rating: 4.9127088 out of 5

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Id: 6xoCeliJ11Q

Length: 15min 51sec (951 seconds)

Published: Sun Jul 05 2020