What are Eccentrically Cycloidal Gears? 

oh, now that’s a brilliant idea. that’s what I love about doing videos - I get the best feedback ever!

one big advantage of this approach over putting it on the inside is that this doesn't require large bearings, pins, etc. this can be scaled up to very large gear ratios while still using cheap 608 bearings. Although, I could see the potential for a large gear that has a solid disk on one side, possibly pinching the edge of the gear between the one lobed gear and bearings on the outside

just saw the video, wanted to write the same... so are there updates on this?

@@CM-mo7mv sorry - didn't see your comment when it came in! I did a follow up on this: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-xv5cd7Bg7Uk.html

Absolutely. Discovery channel-like

thank you very much

If you wanted to eliminate the sliding wear, you could use the 180 degree phased approach at 1:08 but use a ball race around each pinion. roller camshafts in auto engines are made like this.

Thank you so much!

thank you very much. let me know how your modelling goes!

no, I had not. that’s a great idea! if you just mirror the pin and disk in the vertical direction then that would create it. I’ll have to give it a go. thank you

Wondering what is a herringbone approach ?

@@BHARGAV_GAJJAR ////// \\\\\\

​@@BHARGAV_GAJJAR when the gears are mirrored to achieve chevron shaped profile like this: »

Thank you! Will do!

Thank you very much!

yeah, I really should have mentioned how easily backdriven it is. whoops! I wonder if this could be used in a planetary configuration and if that would allow higher reductions…

thank you. I think the main reason it’s not used is that it’s really really difficult to machine these forms using standard subtractive methods. however, with 3d printing they are easy to make. I mean, there may well be other reasons too, I haven’t done a load of testing on this yet, but I’ll cover that in a future video.

This sounds really interesting, but I'm not sure I understand- do you have a reference?

What does that even look like?

thank you very much. yeah, but the difference here is that worm drives work through sliding friction, but this works only with rolling friction which has much lower losses

@@roTechnic : I'm a little confused by that claim. The pin (at least when it's contacting at its largest diameter) has to slide across the surface of the large gear, yes? And wouldn't that give you sliding friction? What am I missing?

@@roTechnic I'd have to disagree about the "only rolling friction" part. Since this is a 1:N gearing, just like in a worm gear AND height of both gears are the same, the length of contact of the small gear must be much greater. In fact this is another form of a worm gear but with parallel rotation axes. Thanks for introducing me to your idea though, might be useful for me sometime.

Would be interesting to see how small the parts/curves could be printed for larger reductions and more compact mechanisms

thanks for your comments - both are great ideas - I’m definitely going to try shrinking it in the future and may see if I can get the pin internal to the disk. the only question is how to hold the top of the pin - at the moment it has a bearing on it which mounts into the housing and stops any flex

try it bro!

How would you transfer it? Also, I want to make a 3d Printed Cycloidal Drive Box. Not able to decide whether to print this 1 tooth gearbox or a full fledged one. This seems like a simple gear attachment that is split to be continuous. Whereas the cycloidal drive has a complete different mechanics.

I’ve got a bit of backlash at one point in the rotation. I think it’s due to my 3d printer needing a bit of calibration and the arc which it occurs in is only a couple of degrees. everywhere else has no noticeable backlash. and, yes a bit of PTFE silicone grease would help greatly, but it looks dreadful on video 😎

thank you very much. before I choose one of these designs for my robot arm build I’m going to do a stress test of them - leave them running for a few days. I’ll publish the results in a future video. oh, and let me know how the print goes

thanks

thank you very much. as it’s a cycloidal design, the pin rolls around the disk instead of sliding. most of the friction comes just from inaccuracies in the 3d print..I’d say that this has lower friction than my cycloidal drive of a similar size

@@roTechnic ho !! yes now i understand better !! thanks for the info , i think i will go for made one :)

Hahaha! I did exactly that in the next video! Let me know what you think of it...

interesting! If by strong you mean "how much torque can it transmit?" then the normal cycloidal drive wins because of the increased surface area in contact at any given time (especially if you have multiple offset rotors). However, in my testing, I've found that the limiting factor is the motor rather than the gearbox - both these designs will handle the torque generated by a NEMA17 stepper. If you start using brushless motors then you may see a difference...

ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-soCIkuO6VmQ.html

Love your design. I’m hitting the same issues myself with the internal version, but I think that by reducing the contraction and pin size I’m getting somewhere. Did you find with your internal version you got an extra node on the disc?

@@roTechnic yep, one extra node. I believe that works in our favor though for extra reduction.

Hi, that's partially true, although in my experience, stepper motor holding torque is dependent on the voltage, current, driver choice etc. Instead of working out the efficiencies I've chosen to use the same setup on a number of different reduction mechanisms and see what the torque is - for my purposes, this works fine but YMMV. Comparing to a spur gear reducer is difficult as the efficiency will depend on the pressure angles and amount of backlash (and of course the quality of the prints) but I'd say this is as good if not slightly better if you are aiming for very low backlash - mainly because the form is more tolerant of the way that 3D printers produce parts. Wear on these is supposed to be negligible as long as you chose the right lube.

not really. in a work drive there is sliding friction so it wears. in this, there is ideally only rolling friction which is much lower

You could combine the above with 90 degree conical gears to bring the motor parallel or a centered worm gear to have the motor inside the arm. Alternatively, belt or gear drive the motor to integrate it vertically in the arm. Apart from adding ratio reduction of ie. /2, this way even a second synched motor can be added, to drive both sides of the pin.

That's a really good point about the angle being the main ratio driver - I had not considered that before. Thank you

Yes, you're absolutely right - if this was being made out of metal, using subtractive technology it would definitely be easier to make multiple "steps" instead of a smooth surface. With 3d printing (additive) the smooth surface means it prints easily and doesn't need supports.

ignoring cnc (the obvious answer) this could be treated like a thread with a huge pitch (22mm, not sure if my lathe could do that) and a massive round thread form

thank you. I’m using the large bearings because I want to eventually have this in a robot arm, and the larger the diameter of the bearing the more it and the plastic will resist twisting forces.

you could probably go down to about 4:1 reduction, the shapes produced are not really suitable for low reduction ratios as the smaller the reduction, the more precise the shape has to be, and especially if you are 3d printing it, you'd be hard pushed to get the precision you need. The shape is generated using a plugin I wrote for fusion 360 and I covered how it works and how to use it in a previous video "Designing a cycloidal drive in Python and Fusion 360".

@@roTechnic Alright, thanks so much for your answer! With that in mind, do cycloidal gears only produce gear ratios of integers n:1 or are there gears that could mesh that could have a ratio of say 9:4?

@@inoojo4780 I'm sure it's possible to design a pinion with more than 1 tooth which would give you varying ratios like you've described. But I'm afraid I haven't spent any time on the maths for it :(

@@roTechnic Got it, thanks again!

Hiya, the best way to increase he size of the gear is to change the number of pins or the pin circle radius. increasing either of these will increase the size of the gear, but only the number of pins will change the reduction ratio of the gear.

@@roTechnic I have been trying to recreate your base that uses the EC gearing for my robotic arm but, I am have a bit of trouble. Do you mind sharing the specs of the larger EC gear used in the base (pin_radius, pin_circle_radius, number_of_pins, contraction)? Thank you for the help!

Yeah, a couple of other folks have suggested that and I think it's a great idea. The only thing to work out is how to hold the top of the pinion steady - currently it has a bearing on the top which is held by the housing - any ideas on how to do this if it's enclosed by the larger gear?

@@roTechnic you can have a bridge tower come up from the base to support the top, the housing would have to have room for it (or a hole in it's center) to give clearance, but it should be straighforward to do.

Yep, you're right - why didn't I think of that 😅

For example, planetary gears work fine with single sided bearings.

@@falkgerbig7787 yeah, they do, but this has a fairly large moment at the top which needs a bearing to counteract it

This drive has less friction than the cycloidal drives I've made in the past, but I've got no real way to measure the losses due to friction - and it's these losses which will hinder backdrivability. Have you got any ideas on how to measure them?

@@roTechnic You can measure force (ie. torque) in and force out i guess. Any difference from the calculated one (deriving from the ratio) should be losses due to friction or other causes. You can also find papers on friction in ie. helical gears (long reads) on the subject online.

great idea, I’m going to try that for the next video!

Glad to hear you've made one! yes I found the concept at www.ec-gearing.com/ and worked out how to design a similar system myself

I don’t think so. in this mechanism, the pin is rolling over the disk, so there should be minimal friction. if it was sliding - like a work drive does - then bearings would definitely help. however, I’m always up for being wrong about these things 😂 so if you disagree, please let me know

@@roTechnic I hear this sliding vs rolling friction in cyclodial gear discussions a lot, but then James Burton mentioned that going from sleeves to bearings for his pins made a big difference (although he admitted it wasn't quite a proper cyclodial gear at the time). It will be interesting to see how it holds up over time (power it and see how long it can last)

there will be friction induced by the non canonical shapes due to manufactiring tolerances, 3D printing in this case.

the stepper is rated at 42Ncm, but the torque produced is very dependant on speed (and current, driver choice etc). That's why I'm not really comparing it to a bare stepper, I'm really just looking for a total package which will give me the torque I need for an robot arm project I'm working on.

If the driver provides the maximum current for the stepper, it would deliver its maximum torque at stall. Thus one could calculate the efficiency, but I don't think that this really matters for a hobby application.

Hiya, I'm using the same code as in my cycloidal drive video - it's posted here: github.com/roTechnic/CycloidalDesign You should just need to adjust the pin diameter to something like 15mm and the PCD to your gear diameter. Let me know if you have any trouble changing the parameters - I'm always happy to help!

​@@roTechnic Thanks! So I'm doing something wrong. From the calculations on screen of your cycloidal drive video ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-y9vLVXjz2c0.html "Designing a cycloidal drive in Python and Fusion 360" at 2:09, I plugged the following values into the fusion 360.py code from the github link: pin_radius = 7.5 (bc PCD 15mm), pin_circle_radius = 21 (bc PCD 42), number_of_pins = 12, and left contraction (which I think I need to eliminate altogether to get what you have above at 0:45, but I won't be surprised to be incorrect) at .2 Idk how to upload an image of the result, but suffice to say it's nothing like 0:45 above. So I then tried reversing the convex to concave by applying the changes you made on your video ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-xv5cd7Bg7Uk.html "an easier robot arm actuator..." starting at 2:06, but still get the result that you did (how odd) of convex and not what I'm trying to get at 2:02 of same video ( ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-xv5cd7Bg7Uk.html ) or BETTER, at 0:45 in the video above these comments, "What are Eccentrically Cycloidal Gears?". Help please?

@@Upekrithen I think your problem is that you are trying to fit too many pins which are too large into too small a pin circle radius. If I take your numbers and increase the pin circle radius to 40 then it looks about right. If this doesn't help, feel free to email me on the email in the about section of my channel, you can attach pictures that way. One other quick hint would be to prototype your numbers using "pyplot cycloid.py" which i have put in the same repo. this will show you more detail about what everything would look like, and then once you have something which looks good you can take the numbers over into the fusion add in

​@@roTechnic Thank you very much. I realized that (as you said) the measurements are in centimeters, so I changed pin_radius = .125, pin_circle_radius = 1.5 number_of_pins = 11 and contraction = 0.2, and that very nearly gave me what I need for the disc. I appreciate your time and assistance.

the main drawback of worm gears is that they transmit torque using sliding friction which makes backdriving more difficult as the reduction ratio increases and also has power losses as the torque increases. EC gears on the other hand teamsmit torque using rolling friction (well, they do within the tolerances of the printer) which is markedly more efficient and allows for back driving even at high reduction ratios

@@roTechnic Is there a variant of this like a ballscrew?

@@daliasprints9798 Never seen one, and I can't visualise how it might work as ballscrews have to slide to move. However, it should be possible to make a low friction, high reduction rack and pinion with this technique to give linear motion - that could be an interesting project...

thank you!

Yeah, you and me both! I can see how it could be done with a 4th axis on a CNC mill, but maybe there's a way with a helical milling attachment on a manual mill. Let me know if you come up with anything!!!

thank you

No, worm gears work by sliding friction between the worm and the wheel. This works through static contact and should have minimal friction and therefore wear

it's not a worm gear, worm gears work through sliding friction which makes the whole system very inefficient. this works through rolling friction which means that the transmission is a lot more efficient than worm drives

@@roTechnic The distinction between a worm and a helical gear is that at least one tooth persists for a full rotation around the helix. If this occurs, it is a 'worm'; if not, it is a 'helical gear'. A worm may have as few as one tooth. en.m.wikipedia.org/wiki/Gear

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