How this bizarre pericyclic transmission works? What makes them so cool?

this is a pericyclic gear box consisting of just  four bevel gears and its biggest difference from   conventional gears is clearly this weird wobbling  motion which provides extremely high gear ratios   this one for example here has about a 41 gear  ratio and see it's super slim and pretty compact   but still not an insanely high gear ratio  you could achieve this with a worm gear too   and it would be quite compact now here we have  also got just four gears but this one has a 49   gear ratio hard to believe right there's a 49  times difference in speed and torque between   the input and output look even though I'm cranking  the handle fast the output shaft barely moves it's   super slow by the way I'm sure you are thinking  this gearbox will vibrate like crazy which as   you can see it really is look at high speeds it's  wobbling so fast it's called nutation by the way   and this unbalance kind of tears the part destroys  it but luckily there's a pretty neat solution to   this basically you add another set of gears to it  and it sort of balances out this motion by the way   there is no extra mechanism in the system for this  nutational movement it's just that as the shaft   rotates the gear continuously moves up and down  and the source of this is the inclined surface   on the shaft I was able to machine this inclined  surface on the lath but it was a bit complicated   and getting a nice surface finish wasn't easy  so I basically combined a straight shaft with   a certain nutation angle with an inclined shaft  and 3D printed it I then screwed this yellow gear   consisting of these two parts and placed it on the  inclined surface with bearings look when the shaft   is in this position this point is up so the gear  is facing upward as the shaft rotates this point   comes down and now the gear is facing downward in  this way as the shaft rotates instead of rotating   at the same speed as the shaft the gear makes a  nutational movement by the way there's no rigid   torque connection between the yellow gear and the  shaft so to provide the necessary torque to the   system a reaction gear is added you turn the input  shaft the yellow gear makes notational motion   engag with the reaction gear at the back takes the  required reaction force and thus drives the output gear if I release the reaction gear by the way  the gear ratio is broken see all three start   rotating at the same speed like a clutch and if  I hold the output gear the reaction gear rotates   in the opposite direction by the way there's  generally a difference of one or two te between   the ma in Gears in the gearbox when there's a  difference of one to a gear disengaged from one   slot past a toot and re-engage to the slot next to  it and a two toot difference cause it to skip two steps so when you turn the input shift the  the yellow gear and the gear in front of it   connected to it rotate two steps backward then  the interaction between the front gear and the   orange output gear rotates the output gear  one step forward this time as a result for   one full rotation of the shaft at 360° the  orange output gear only rotates 8.5 de and   this roughly translates to a gear ratio of  about 41 times and you see while the input   shaft is rotating around 180 RPM the output is  indeed extremely slow just four revolutions by   the way I made another version of this and got a  transparent cover made by JLCPCB so I could see   what's happening while it's working this was  produced using JLCPCB CNC Services it looks   pretty good honestly and let's see if it's back  drivable I can turn it easily from here but from   here no I can't turn it it's like stuck you know  what I mean it's not back drivable the process   is very simple upload your design choose the  material options include aluminum copper or   plastic and within a few hours you get a quote  they made and shipped the cover in just 3 days   which was quite fast and smooth JLCPCB has mid  year sales going on right now so if you need   pcbs 3D printing or CNC Services it's a great  time for example besides resin or nylon prints   they offer SLM 3d printing which lets you print in  stainless steel they create the model by melting   Steel steel powder and results in genuinely solid  steel all right this is the one with a 49 gear ratio okay let's turn it is it working I can't  tell it's moving it's really slow and for just   one full rotation of the output shaft I  would need to turn this handle 49 n times   how slowly it's turning so what's Happening  Here Right Now the wobbling gear rotates one   step forward at the front but before that  it also rotates one step backward at the   rear so in total when the input shaft makes one  full turn it rotates a very small amount just   as much as the difference between these two  movements this gearbags naturally generates   very high tooth forces even with small input  torqus due to the extreme high gear ratios it provides if I were a plane one new to  meter with this motor right now I would   have obtained around 400 Newton meter  of torque at the output which as you can   imagine is quite high and notice this happens  in just one stage so how can the gear til with   these high torqus so another great thing about  this gearbox for example in a SP gear during   engagement only one tooth is in contact so all  the load is concentrated on that single tooth   but in this gearbox look during engagement many  teeth are in contact this means that the torque   Lo will be shared by all the teeth in contact  resulting in smoothly transmit High Torques   and also quieter operation the movement of the  gearbox as you can see is a bit unstable and   this unfortunately doesn't allow high speeds right  now the input is around 600 RPM and look how it's   vibrating in slow motion though you can see that  the yellow gear is actually rotating quite slowly   compared to the input shaft the problem here is  the notational motion it's making which as you can   see is quite fast and at the same frequency as the  input shaft let's increase the speed to around,   1500 RPM and the gear box is practically  [Applause] working when I increase the speed   even more first the screws start to loosen  and then the whole gearbox starts to fall apart the main reason for this is the fluctuating  axial forces caused by the unbalance of the yellow   gear this motion creates gyroscopic moments that  act on the gear box housing along the shaft axis   and their effects can sometimes be greater  than the mching forces the simplest solution   is probably not to operate at high speeds  to completely eliminate this an identical   gear unit is added to the end of the gear unit  which balances the system however this has a few   drawbacks as you can see getting output from the  gear box becomes a bit more complicated so I added   a spur gear in the middle moreover the required  number of Gears bearings is now doubled due to   the mirroring and naturally the gearbox has become  larger and heavier I printed all of these by the   way I'll add the sdl files of all the designs in  the description so you can print and Tinker with them all right let's turn it it has got a very smooth rotation doesn't it  kind of relaxing but honestly I don't feel   anything different from previous version  it still feels a bit unstable anyway look   this is the first pericyclic unit and this is  the mirrored one since the shaft is one piece   I can drive both with this handle and because I  set them in opposite positions their notational   movements are in opposite directions you see  which cancels out the axial unbalances the   overall gear ratio of the system is the same  as a single unit about 41 it hasn't changed   now let's set the other counter gear here  the torque will decrease by one and half   times and the speed will increase by  one and a half times let's give it a turn now with this handle I'm turning which is the   input shaft there's about a 27 gear ratio  between this and the aluminum extrusion output let's increase the speed a bit [Applause]   look at them spein around 1,000 RPM and  everything seems fine it's going well I [Applause] think there's still some vibration but it's not   because of the gears check this out  the yellow gears are nutating so fast   that they just appear to be spinning but they  are actually nutating at an extremely high speed it's much better than before and the gearbox   as it is now is more reliable and we  can get extremely high torque from it it's just a bit too noisy but of  course we can't expect it to be as   quiet as a magnetic gearbox I made before  by the way a non contact magnetic gearbox   is really interesting if you haven't  seen it you should definitely check it out now I was intending to lift a few real objects  but you see since I designed the gearbox more as   a model this weak housing design doesn't really  allow for a significant load it flexes sideways   on the load causing the gears to skip the same  thing happened with the other design by the way   but if I press it like this from  the sides it works just fine no   skipping gears and it's really  powerful it just needs a solid casing and now I remember I made a  version like this too let's give a try that's all I have to say about these  gears do you think they are useful or   just unnecessary thanks for watching if you liked  it please subscribe and check out my other videos.

Channel: Retsetman

Views: 45,026

Keywords: pericyclic gears, nutation gearbox, pericyclic transmissions, nutation transmission, 3d printed gearbox, harmonic drive, wobbling gears, oscillating gearbox, gear ratio, gear reduction, high torque, experiment, 3D printing, design, make, strain wave gears, cycloidal gears, bevel gears, 3d printing, 3d print, gears, gearbox, mechanical, engineering, spur gear, worm gear, reduction ratio, torque, gear ratio explained, what is torque, 3d printed gears, 3d printed

Id: Z-zUTS5FPPc

Length: 11min 38sec (698 seconds)

Published: Mon Jun 17 2024