Build the World's First (patented) Geared CVT [Studio file included]

[Divitis]

I was looking for a CVT for my next project when this came up: 

 

About a year ago an Italian start-up got a patent for a gear based CVT transmission module (however there seem to be earlier implementations of ta very similar system). The video above illustrates its inner workings in detail.

Obviously, I could not resist and had to recreate it. But as I'm spending summer far away from my Lego, all I could produce is the digital model, which you can download here -> https://bricksafe.com/files/divitis/miscellaneous-/CVT.io

Now, do we have a volunteer with a good supply of bricks and time on their hands (I'm looking at you @Auroralampinen) who wants to build it and test it out for the community?

It's a no-motor setup, meaning one has to turn the yellow banana gears by hand, but hopefully it's enough to see if and how this works out with Lego.

Note: The original uses small electric motors to control the displacement of the arms attached to each of the sun gears. I devised a mechanical system to do that, and that's what the black 16t gear which sticks out is for. It controls the displacement of the upper arms through the red differentials. When the diffs are stationary, the blue 12t gear above spins at the same speed as the 28t turntable and the rack doesn't move.

More info available to the brave and the curious :)

[2GodBDGlory]

Wow, that is so cool! I think I saw a headline about that a few months back, and thought it would be super cool to try to realize in Technic. However, I guess I was busy with other stuff, because I never even got around to trying to understand the design in the first place.

I'm super excited to see that you recreated that! I'd love to try a test build of it, but I've only got four of those banana gears, so I'll have to leave that to someone else.

Very nice work!

It brings to mind this design I put together years ago, in that both operate on varying the pivot of a linkage, but the real-world prototype and your design are way more sophisticated! I'm not sure my design is actually a CVT, since there's 16 fixed positions on the output gears, and so some discrete number of teeth has to be advanced in one rotation: https://www.youtube.com/watch?v=gceNC7GKbBQ&ab_channel=2GodBDGloryLegoTechnicVideos

 

[Auroralampinen]

7 hours ago, Divitis said:

I was looking for a CVT for my next project when this came up: 

 

Now, do we have a volunteer with a good supply of bricks and time on their hands (I'm looking at you @Auroralampinen) who wants to build it and test it out for the community?

 

Well, i do have a lot of time because i don't work(bacause of my mental issues) :).

[Divitis]

3 hours ago, Auroralampinen said:

Well, i do have a lot of time because i don't work(bacause of my mental issues) :).

I am sorry to hear. I had no idea and apologies if my comment was inappropriate in any way.

 

7 hours ago, 2GodBDGlory said:

I'm not sure my design is actually a CVT, since there's 16 fixed positions on the output gears, and so some discrete number of teeth has to be advanced in one rotation: https://www.youtube.com/watch?v=gceNC7GKbBQ&ab_channel=2GodBDGloryLegoTechnicVideos

That's an interesting prototype, even though technically you're right that it's stepper operated.
From what I read the problem with ratcheting CVTs is that the output isn't linear. I reckon the four arms inside a planetary gear help with that, but then they further smoothed it out with elliptical gears (not sure how that works but we don't have those in Lego anyway)

 

So, no takers? with 4 diffs, 5 turntables and 16 banana gears laying around? ;)

[PlasticGear]

Incredible ! I was also looking at this mechanism but didn't let it a go. It seems massive.

Can't wait to see it in action ! I am a bit worried tho, since it is an asynchronous mechanism, how it will behave with the lego gear slack.

[Auroralampinen]

5 minutes ago, Divitis said:

I am sorry to hear. I had no idea and apologies if my comment was inappropriate in any way.

 

 Nope it wasn't inappropriate i actually smiled and yes, i have fully accepted this, that i have become a meme, for that i have always a lot time to build lego's😄

 

Edit, i have seen much worse stuff in my life, because i was school bullied, so the bullying ruined my mental health:/

Edited August 14, 2025 by Auroralampinen

[Davidz90]

Very interesting! Great job recreating it.

For the real thing, I have some doubts regarding the durability of the ratcheting mechanism in automotive applciations. Nevertheless, this is a really clever solution. 

[Jundis]

1 hour ago, Divitis said:

From what I read the problem with ratcheting CVTs

Thats exactly the point here. To make this work, you need a ratched mechanism that rebound (or whatever the "slipiing back" is called) is near to zero. With Lego bricks, this is nearly impossible to recreate.

Still what a fantastic effort to make a brick version of this beast! 

[N1K0L4]

I love the design if the real thing, really clever.

All congrats to you for making this massive build! I hope someone builds it.. (don't have the parts either, sry)

[2GodBDGlory]

On 8/14/2025 at 4:19 AM, Divitis said:

So, no takers? with 4 diffs, 5 turntables and 16 banana gears laying around? ;)

Well, thanks to a generous Eurobricker who reached out to me and offered to ship me the parts I was still needing, I should be able to give this a test build at some point! I won't be able to start for at least a couple weeks, and I'm not sure how long shipping will be (so maybe you'll be back at your own Lego by then), but I'll be giving it a build at some point!

[Divitis]

7 minutes ago, 2GodBDGlory said:

Well, thanks to a generous Eurobricker who reached out to me and offered to ship me the parts I was still needing, I should be able to give this a test build at some point! I won't be able to start for at least a couple weeks, and I'm not sure how long shipping will be (so maybe you'll be back at your own Lego by then), but I'll be giving it a build at some point!

That's great news!

And nothing like an anonymous donor :)

Timing works, I won't be back at my Lego desk before a month or so anyway,.

Also I must confess that I'm one differential short myself .Maybe I'll decide on ordering one more dased on your feedback. 

[2GodBDGlory]

I picked up the last of the necessary parts today, and started building! However, I have ran into an issue:

When building physically, it becomes apparent that these 4 36T gears interfere with each other, and just won't mesh in that configuration. I've came up with an alternate gearing option, which could work in theory, but it will require some adjustments to the frame:

[Timewhatistime]

9 hours ago, 2GodBDGlory said:

When building physically, it becomes apparent that these 4 36T gears 

Is this really the setup from the digital model - with four 36T gears and one 12T gear situated in the same layer and supposed to mesh with each other?

Edited September 3, 2025 by Timewhatistime

[2GodBDGlory]

2 hours ago, Timewhatistime said:

Is this really the setup from the digital model - with four 36T gears and one 12T gear situated in the same layer and supposed to mesh with each other?

The 12T gear is one layer up, on a fifth 36T gear, so we're not running into the issue of having gears trying to rotate different directions at once; it's just that the 36Ts on the same level don't quite fit that spacing

[Divitis]

2 hours ago, 2GodBDGlory said:

it's just that the 36Ts on the same level don't quite fit that spacing

I'm really sorry that's proving to be an issue, I thought 4 gears in that configuration would mesh smoothly enough, and in theory they should, no?

Are they too tight?

[2GodBDGlory]

1 hour ago, Divitis said:

I'm really sorry that's proving to be an issue, I thought 4 gears in that configuration would mesh smoothly enough, and in theory they should, no?

Are they too tight?

I'm not sure what the theory around  them would be, but yeah, they're too tight. If you look at the screenshot up there, you can kind of see that the spacing between the body of the gears is pretty small, and smaller than the height of a gear tooth.

Fortunately, I figured out some bracing for my workaround gearing strategy, and it seems to be working, with all the gears rotating at the same speed in the same direction, with only relatively minor changes! I ran out of time last night to finish the build, but hopefully I can get it done today

The only other issue I've found (I'm pretty sure it's not by design) is that the 1L liftarms on frictionless pins mounted on the DBL 7L alternating hole liftarms on top of the 15x11 frames interfere with the rotation of the large banana gear assembly, since the tan 4L axles interfere with them. I just removed them, and I expect it'll be fine like that?

[Divitis]

3 hours ago, 2GodBDGlory said:

The only other issue I've found (I'm pretty sure it's not by design) is that the 1L liftarms on frictionless pins mounted on the DBL 7L alternating hole liftarms on top of the 15x11 frames interfere with the rotation of the large banana gear assembly, since the tan 4L axles interfere with them. I just removed them, and I expect it'll be fine like that?

Oh poop! Quite a basic case of 'building digitally where everything is stationary'!

I only put them there to support the banana gears from below, so if you feel they are not needed, toss them away. Otherwise, maybe they can be moved to the last holes of the dgb flip flops maybe?

Very glad to hear the progress on this. My Lego is still all in moving boxes!

[2GodBDGlory]

I got the gearbox built now! I think the main other things I had to change were adjusting the worm gear at the bottom, and changing the ratchets on the top, since those connectors didn't interlock with the 8T gears satisfactorily in real life.

Also, I don't really understand the theory behind the gearbox, but I think something must be off with the 7L gear racks, because the way I see it, these blue gears can't actually rotate to move the rack, because doing so would mean moving the LBG 5L beam with which the gear is braced.

That area in general feels like it's missing something--should there be some rubber bands to press the 3x7 bent beams against the sides of that ring gear? There also doesn't seem to be a whole lot to hold the rack in place, but again, I don't really understand the theory behind it.

My one other question is how is the gearbox controlled? We've got the worm gear driving the 8T gear on the bottom, but is that the input shaft or is it controlling shifting? I assume the red Bohrok eye on the top is the output, but is there a third input/gearbox control somewhere else?

I look forward to working through these things to get the concept working! Good job designing such a complex model digitally--that's a huge challenge!

 

[Divitis]

5 hours ago, 2GodBDGlory said:

That area in general feels like it's missing something--should there be some rubber bands to press the 3x7 bent beams against the sides of that ring gear?

In the real life version, there is nothing.

 

5 hours ago, 2GodBDGlory said:

We've got the worm gear driving the 8T gear on the bottom, but is that the input shaft or is it controlling shifting?

That controls the shifting of the racks, their 'eccentricity'

 

5 hours ago, 2GodBDGlory said:

I assume the red Bohrok eye on the top is the output, but is there a third input/gearbox control somewhere else?

The input is the banana gears, which one would have to spin by hand. Not super practical but I thought it'd be enough to see if things are working before complicating things even further.

 

5 hours ago, 2GodBDGlory said:

something must be off with the 7L gear racks, because the way I see it, these blue gears can't actually rotate to move the rack, because doing so would mean moving the LBG 5L beam with which the gear is braced.

Yes. My bad again. For now the simplest solution is replacing the 7L axle on which they sit for a 5L one and leave them without bracing at the top. Given things move slowly it should still work.
I also noticed I only included one bracing/stopper for the 7L rack (the white 1L liftarm). Another should probably be placed on the other side of the 7L rack.

 

5 hours ago, 2GodBDGlory said:

I look forward to working through these things to get the concept working! Good job designing such a complex model digitally--that's a huge challenge!

Thanks! Kudos for your patience :)

[2GodBDGlory]

Sorry for the delay in updating my progress!

I think I understand the theory now, and I made some more tweaks to the area with the 7L gear racks, so they're now able to rotate the full 360 degrees. This also required moving the small banana gears up one stud.

Unfortunately, in its current form, it's not really working.

There's some pretty major backlash problems with the 12T gears driving the gear racks, such that the racks can move freely about a stud, which is a pretty crucial difference. Getting rid of the backlash might be tricky, but I wonder if replacing the rack with a small linear actuator might work. It would be even bulkier, but the screw would prevent any backlash from causing issues.

Beyond that, the actual ratcheting part at the top isn't really working. Part of the issue is that the eccentric moving the arms is so much lower (worse now that I moved the output ring up) than where the 12T gears engage with the banana gear, but it's just generally floppy and imprecise, at this point in development.

I think solving these problems is going to require fairly significant re-engineering, so I think this is where I'm going to stop working on the project (at least for now, since I've got other projects waiting), but I hope you can put in the work to get it working!

I do feel like the required precision and inherent complexity are right on the edge of what is possible with Lego, but I think it can be done! I'd recommend moving to a physical build at this point, though, since there is so much moving, and since so much depends on countering the slack in physical parts.

I've updated the Studio file with my changes (mostly in green parts), and I've also uploaded a quick video of what operation looks like for me:

https://bricksafe.com/files/2GodBDGlory/miscellaneous/Divitis CVT.io

Good luck with the project, and thanks for sharing!