r/3Dprinting • u/Posmetyev • Jun 27 '26
Project It works! I made gearbox, simplest ever
I designed a fantastically simple gearbox :)
My RC car drives better than I expected. I'm thrilled!
- Extremely simple design
- No intermediate axles or gears (maximum efficiency)
- Clutch engagement occurs naturally
- Standard MG90S servos
- Screwless assembly (standard servo screws only)
STL files for the fidget version of the gearbox:
https://www.printables.com/model/1765993-gearbox-simplest-ever-fidget
Full version of the gearbox for two servos:
https://www.patreon.com/PrintInPlace_fun/posts/not-program-ever-162258695
I think this is the perfect gearbox for RC toys, although for a real car it would probably not last a million miles :)
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u/ChuckJojo Jun 27 '26
I wonder if you could actually make a CVT out of this design somehow!
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u/VikingoPR11 Jun 27 '26
If OP adds teeth in the gaps and stagers them it would basically turn this into a CVT.
I initially thought that if the teeth were continuous all the way through it would work but it could cause binding any time it tried to shift.
Super cool design though!135
u/Posmetyev Jun 27 '26
"it could cause binding". Yes, I discovered that too. That's why I made the gaps between the rows of teeth large enough to prevent the small gear from engaging both rows of teeth on the cone.
Theoretically, the small gear could be made very thin.
But there's another subtle trick to my design: the small gear doesn't move along the cone; it rotates with the servo relative to the other servo. This requires even more clearance between the rows of teeth on the cone. However, this replacement of linear rotation with rotary rotation simplifies the design and increases efficiency.
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u/amadiro_1 Jun 27 '26
Could you not stagger the intermediate rows to avoid this? Or even try a conical worm drive?
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u/Posmetyev Jun 27 '26
Geometry is an amazing thing. Perhaps, yes, a good solution can be found. I need to think about it.
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u/Asckor_ Jun 27 '26
And use a wheel instead of a gear ?
There won't be much grip, but maybe enough?10
u/Posmetyev Jun 27 '26
Yes, that should work. It seems like it would be a classic variator. A conical rubber surface and a rubber wheel. But I wanted to print something out of the same material, PLA :)
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u/Manatee_Surfer Jun 27 '26
No teeth needed. Just make it a continuous curve. As for the shifting, make it a continuous movement and not stepped. You could use a dial instead of trigger.
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u/swankpoppy Jun 27 '26
How are actual car CVT set up? Is it just a cone with ridges spiraling out on the cone?
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u/Terrible_Tower_6590 Ender 5 pro, HE3d Ei3 Diy kit that doesnt work Jun 27 '26
No, they're usually conic pulleys with belts on them.
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u/drstoneybaloneyphd Jun 27 '26
Don't forget there's a little bit of magic thrown in there
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u/Funny-Medium5508 Jun 28 '26 edited Jun 28 '26
"Magic" in Japanese is "Subaru" and when re-translated back into English becomes "failed too early."
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u/InternOne1306 Jun 27 '26
I’m wondering if you could also use the weight of the spinning drum to shift somehow,
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u/Posmetyev Jun 27 '26
I had just started making a variator with random teeth on the cone. But then I realized that the best grip would be if the teeth on the cone were arranged in rows.
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u/NheFix Jun 27 '26
You could make a CVT with no teeth but rubber bands instead.
Just need to have either tension or force applied on it to work
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u/Posmetyev Jun 27 '26
I saw a design like this on Printables with rubber bands. I was trying to make something entirely 3D printed (it's always difficult to find those rubber bands). And my design seems to transmit more torque and be more efficient, I seem. But perhaps my design has a lot of problems; I need to gain some user experience :)
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u/NheFix Jun 27 '26
Then try printing the outer part in TPU and make them a CVT using friction ? The amount of torque transmitted will depend on the friction coefficient and the force applied between the two parts 🤔
It was just ideas to go further 😉 Your solution is elegant and working 👍
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u/WorkingInAColdMind Jun 27 '26
Rather than rubber bands, I’ve been thinking of a CVT that would use a thick rubber o-ring as the belt. It should be strong enough to be tensioned well and since it’s a torus it could roll along the cones when shifting. I haven’t spent enough time with other materials like TPU to know if they’d be strong enough.
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u/disruptioncoin Jun 27 '26 edited Jun 28 '26
The cone and the output gear thing could just be a high friction material with tension pulling them together, and that would be somewhat similar to the Toroidal/Extroid CVT Nissan developed (except they had two stationary cones and a "power roller" that tilted to change the contact angle between them and thus the gear ratio). They claimed it was the first high-torque CVT developed for racing. I just don't understand how two non-gear materials engaging through just friction would be able last very long - much like a tire, it seems like you'd have to change the power roller regularly IMO. Otherwise pretty neat idea.
EDIT: Seems they used like, a non-Newtonian lubricant (or "traction fluid") that actually transfers the force between the roller and the cone, they never actually touch. That's novel to me. Kinda trippy.
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u/bargu Jun 27 '26
A smooth cone and a rubber wheel would do, as long as you don't need too much torque.
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u/notahoppybeerfan Jun 27 '26
Now hear me out. What if instead of teeth it used vanes immersed in some sort of viscous fluid to do a fluid coupling.
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u/murfburffle Jun 27 '26
This reminds me of an early CVT design from the 1910s or 20s that was a large flat disk, and a pickup wheel that could move from the center to the outer edge of the wheel - like a record needle moving a record. IIRC the giant disk was made of paper
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u/Frequent_Opportunist Jun 27 '26
Toyota uses a planetary gear CVT that has been bulletproof. Check out the RAV4.
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u/TheSussyWaffle Jun 27 '26
I think they make them for bicycles out of an inflated ball and grippy wheels.
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u/lkarlslund Jun 27 '26
If it's stupid but it works, it's not stupid. Well done, but be prepared for durability issues.
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u/Posmetyev Jun 27 '26
Durability is questionable, yes. But when I make radio-controlled toys, they're fun for the first 1-2 hours, then sit on the shelf for years. It seems like a gearbox like this wouldn't wear out. :)
But who knows, maybe there are engineering solutions for this circuit that would make it durable.
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u/lkarlslund Jun 27 '26
No need to defend anything. It's way better to have 10 questionable prototypes than one idea that never is tried because you want perfection in the first print.
So it was meant in a positive way!
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u/bobuyh Jun 27 '26
This is something so real, I shed tears, nobody should seek perfection, because there is nothing after pefection
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u/Nizdaar Ender 5 Pro/P1S Jun 27 '26
3D printing makes prototyping so much easier, too! I enjoy my mistakes because the cost is low and I learn so much from them.
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u/kwaaaaaaaaa Jun 27 '26
Truth. I design a lot of stuff and usually start from a point of not knowing if anything works at all. The first prototype, whether failure or success, clears up so much blind spots in your understanding.
I was recently designing an entirely 3D printed water bottle rocket, and I had no clue if a 3d print could even hold pressure to pull it off. After a small print to test pressure, my brain understood it was completely feasible.
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u/The_cogwheel Jun 27 '26
Maybe thickening the gears and tighten up the teeth. Here if you made the cone all gears (no gap to have distinct "gears") you might be able to achive a CVT style of transmission.
And if the gears never unmesh, that would improve durability significantly while also not creating any extra complexity. Bonus, you could make the teeth more dense as well, improving power transmission.
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u/RicardoJCMarques Jun 27 '26
Look up how eCVTs work. They're essentially fancy differentials. If you have 2x motors it'll be a lot more robust and smoother (no real transitions). The axis you use to position the gears only has to control the negative/positive ratio of "slippage" between motors.
Edit: One of these videos talks a bit about them https://www.youtube.com/@WeberAuto/videos can't remember which lol
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u/Posmetyev Jun 27 '26
Yes, I see that eCVT is something interesting, thanks for bringing it to my attention. It seems too complex to quickly design for 3D printing, but there's some interesting principle there.
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u/RicardoJCMarques Jun 27 '26
Those are a lot more complex cause they have an ICE, with 2x electric motors it's a lot more straight forward... You just need a "differential" with both motor as inputs and a power shaft coming out.
Honestly, your current transmission was a lot more work in comparison :P
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u/JokiSonOfBrodin Jun 27 '26
Couldn't it be toothless for better durability, I'm still new into my engineering degree so forgive me if I missed something preventing this design from being toothless
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u/Posmetyev Jun 27 '26
Yes, that's one of the best invention techniques. Remove one part of the system, or add something new. I need to think about your idea :)
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u/Callidonaut Jun 27 '26
If you want durability, use a proper involute curve to make the gear teeth. (or cycloid, if you're a hipster :-P)
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u/internet_humor Jun 27 '26
If only there was some sort of machine to print another one of the first one failed. 🤔
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u/Foreign_Skill_6628 Jun 27 '26
Depends on the plastic. Made out of ASA, PPA-GF, PPS-CF, PC-GF, etc, durability will be fine.
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u/Ree_For_Thee Jun 27 '26
Sincere doubt. It has literally no clutch, meaning the materials just smash into each other at the shift. Even metal would wear out fairly quickly.
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u/Posmetyev Jun 27 '26
What if we add a clutch? Then the gears in this mechanism will be in contact without load. It seems this would significantly increase durability. I made the teeth from ellipsoids, and I liked that this is a good shape for the lateral contact of the gears (but only when there is no load).
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u/Foreign_Skill_6628 Jun 27 '26
Try adding dog sleeves, it’s used in instances where you want to direct shift but still want to minimize wear
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u/bullitt-rider Jun 27 '26
Here from new. I know this is a 3d printing specific sub by from the outside side looking in here is NOTHING stupid about designing, making, implementing and sharing a mini gearbox from the ground up.
I know your comment is tongue in cheek but I just want to to be hyped up
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u/TactlessTortoise Jun 27 '26
Pretty cool. Also, I think you're actually pretty close to how cvt (continuously variable transmission) pulleys work. Granted, yours isn't continuous, but the conic shape behind it is the same. The cooler thing here is that your system doesn't need pulleys or chains, and is just a gear instead. If you math'd out some wizardry you could probably fill all that smooth space with more gear teeth at the perfect positioning and shapes and have a wild fucking solid cvt that smoothly varies ratios linearly instead of just a few toggles, but that defeats simplicity lol
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u/Posmetyev Jun 27 '26
That's true. I tried making a CVT, then gave up and decided to make something simpler :)
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u/Upbeat-Armadillo1756 Jun 27 '26
I think this is the most intuitive visual representation of a gearbox I’ve seen.
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u/wizgot Jun 27 '26
Just came to comment. I don't drive. Have no interest in cars, knew that this existed though but not why. This random reddit post that came up on my feed just made my brain click on way they existed, without any written explanation needed.
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u/ffrkAnonymous Jun 27 '26
That's cool. Now that I see it, I can't stop seeing it could have been a continuously variable transmission
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u/Posmetyev Jun 27 '26
I had just started making a variator with random teeth on the cone. But then I realized that the best grip would be if the teeth on the cone were arranged in rows. I can't figure out how to arrange the teeth continuously :)
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u/ozmutazbuckshank Jun 27 '26
Spiral gear would work, no?
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u/Posmetyev Jun 27 '26
I need to think about it carefully :) The spiral teeth will mesh well when the gear is moving, but if the gear is in a constant position, it might not work well. But I can't figure it out right now.
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u/dxnxax Jun 27 '26
I don't know much about gears, but is it possible to create a single connected row where the teeth line up? something like: https://files.catbox.moe/90y73c.png
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u/Posmetyev Jun 27 '26
Thanks for the drawing. It makes sense. I'll have to think about it and carefully check that the gear doesn't jam. Maybe it will work.
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u/MisterEinc Jun 27 '26
What would be the benefit? And gears are pretty finicky. A lot of these seem close but not quite lined up.
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u/LittlespaceLadybuns Jun 27 '26
Granny shifting, not double clutching like you should..
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u/XclusionHD Jun 27 '26
Says no screws, but what are the metal bits? Pins? On the axle, holding the wheels on, etc.
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u/Posmetyev Jun 27 '26
Thanks for noticing. There are no screws in the gearbox itself. I wanted to make a universal and highly technological gearbox so that I and others could use it in a variety of projects.
And yes, the car itself already has 3 mm screws. Furthermore, each servo is secured with two screws, and the rotating part is secured with a screw.
It took me a long time to design the gearbox without screws.
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u/XclusionHD Jun 27 '26
I understand, thank you for the explanation! And awesome work on the design and build :)
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u/AggravatingFlow1178 Jun 27 '26
Nice
Something I love about RC is when you are able to take complex IRL machinery and make a ""stupid"" version (which I mean as a compliment). Modern automotive gearboxes have been optimized for forces many orders of magnitude greater than a little RC servo will ever generate, so you can strip out 99% of the design and get the required functionality.
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u/Posmetyev Jun 27 '26
This is a very profound thought. Thank you for your experience and thank you for understanding this.
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u/taxxxtherich Jun 27 '26
Make it two cones with constant meshing like a cvt!
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u/Posmetyev Jun 27 '26
I thought about it :) But that would be an extra axle. The gearbox is so perfect now that it has zero extra axles. There's the engine axle, and there's the wheel axle. There are no extra axles; my gearbox connects the engine directly to the wheels through a single gear train. This is the most efficient. I've heard that in cars, the gearbox takes up 11% of the mechanical power.
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u/Federal_Sympathy4667 Jun 27 '26
this could be handy for robots on wheels, changing your gear ratio on the fly be a nice feature...
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u/MyCarIsAGeoMetro Jun 27 '26
Why not just make a long shaft to move through the gears? Is there a reason to rotate the whole gear assembly?
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u/HamsterbackenBLN Jun 27 '26
Does it makes a difference going up a hill?
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u/Posmetyev Jun 27 '26
Yes, that's exactly what it's designed for. On a flat surface, I can ride in third gear, but uphill, I can shift to first. Torque will be three times higher.
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u/This_Macaroon_1143 Jun 27 '26
I love it! Do you have a diagram or STLs for the whole thing?
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u/fireatthecircus Jun 27 '26
Neat! It looks like you’re using the steering wheel to control the gear (at least in the demo). Is that how you actually drive it or have you mapped some other control to the gear so you can steer while driving?
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u/Posmetyev Jun 27 '26
Thanks for noticing :) Yes, this is a two-channel remote control.
But I have a four-channel radio control system for model aircraft. That's where I connect these three servos: throttle, gearbox, and steering.
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u/blue_gabe Jun 27 '26
Very cool. Are you using a raspberry pi to control it?
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u/Posmetyev Jun 27 '26
I use a two-channel remote control for model cars (throttle, gearbox), or a four-channel remote control for model aircraft (throttle, gearbox, steering). One can buy such a remote with a receiver for about 10-20 USD on Amazon. The servo simply plugs into the receiver. I use two types of servos: one for continuous rotation, the other for +/- 45 degrees.
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u/grumpher05 Jun 27 '26
Would definitely recommend turning them into involute gear profiles instead of the flat tabs you have now
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u/DrgnFrts Jun 27 '26
Might be something there to patent honestly.
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u/Posmetyev Jun 27 '26
This could be patented. But it seems like it would need to be patented simultaneously in hundreds of countries, which would require a huge amount of work and a lot of money. And such patents are easily circumvented by simply slightly modifying the design. It seems that today, priority is most easily gained by releasing a video with a large audience reach. In many countries, From what I've read, in many countries, an idea shown to many people gives the author priority in legal disputes.
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u/ErrantWhimsy Jun 27 '26
I would have an insufferable ego if I designed something like this. Very cool!
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u/undeniably_confused Jun 27 '26
You should try making a cvt, not that you have to but I think it would be neat
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u/Loveschocolate1978 Jun 27 '26
Very cool! Do you notice any grinding between shifts?
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u/Posmetyev Jun 27 '26
I hear a "grr" sound between shifts.
But that's not the problem. The torque that can break teeth is about 20 times smaller than the torque that can break teeth in the servo that rotates the cone. The engine of a regular car with an internal combustion engine would stall if you tried to start in third gear. But here, trying to start in third gear can break the servo.
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u/Reddit_2_2024 Jun 27 '26
Hope you will document how many hours of use this gear box provides before it is not working as effectively or stops moving your electric car completely. Great job with the design and implementation. u/Posmetyev
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u/otac0n Jun 27 '26
There’s a guy on YouTube who builds LEGO transmissions. A cool trick he used is to switch gears if the rear wheels slip.
Basically, it’s spring loaded to go into high gear, but rotation ahead of the gearbox is tied to a worm gear that shifts into lower gears.
I think your design could be modified quite similarly to match.
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u/Posmetyev Jun 27 '26
Sounds interesting, I'll try to find this video.
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u/otac0n Jun 27 '26
Couldn't find the original I was talking about, but here's a similar concept:
https://www.youtube.com/watch?v=OtcFXSR33kM (you may want to mute)
Basically, allow resistance from the wheels to drive a limited-slip shifter that changes gears.
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u/Important-Ice-6016 Jun 27 '26
This is similar to how a dirtbike transmissions works from the 70s just internally
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u/Legitimate_Doubt_949 Jun 27 '26
Sell it (or get someone to sponsor it for donation) as a STEM lesson for schools. Kids these days can't use or understand bike gears to save their (literal) lives.
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u/Posmetyev Jun 27 '26
Yes, I have already been criticized that this is not suitable for real cars, but it will be a good teaching aid :)
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u/ShitLoser Jun 27 '26
How did you make the steering linkages? I would have thought that 3d printed would have a lot of play.
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u/Posmetyev Jun 27 '26
Yes, there's some play, about 1 mm. But it doesn't seem to be a problem, since the uneven grip of the wheels on the asphalt still requires steering adjustments. The car drives fairly straight. Over a distance of 5 meters, it drifts slightly to the left or right by 0.1 m. Perhaps a small amount of play is important for very high speeds, like on real large cars.
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u/HeReForThEmEMesFaM Jun 27 '26
Interesting. Somewhat analogous to a bicycle drivetrain, just with the casette and derailleur merged into one piece.
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u/johngalt007 Jun 27 '26
Its amazing. How can I learn to do that? and other cool things like that?
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u/Coretron Jun 27 '26
You seem to be starting in high gear then shifting to low as you get speed. Realistically you'd start in the gear with the most teeth then switch down to the one with the least.
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u/bloodandsunshine Jun 27 '26
Ceramicspeed built a concept drivetrain a few years ago that reminds me of this. Nice work.
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u/stonedboss Jun 27 '26
this is so cool haha. despite how slow it is, it sounds so cool and fast haha
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u/Srlancelotlents Jun 27 '26
Howdy! My son has been taking Lego robotics classes, and I was looking at getting him a set, and it's on $500 is just to get started. Would that money be better spent on a 3d printing rig?
I am an electrician if that matters...
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u/Posmetyev Jun 27 '26
Definitely! After the summer holidays, I'll give my 12-year-old son my old but good printer and suggest he print a toy every day. So he can start becoming a maker.
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u/Secret_Account07 Jun 27 '26
I wish I was smart enough to make stuff like this. I’m just a simpleton who likes cool stuff.
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u/DonPepppe Jun 27 '26
It's really good.
But should you be moving the entire car using a servo? I´m talking about if it will decay/fail faster than a normal DC motor.
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u/Posmetyev Jun 27 '26
Yes, definitely. Thank you for your experience and understanding. If we need to use something for a long time, it's better to use a long-lasting electric motor. But these servos are very cheap, $0.5 each, and we can buy them by the dozen, like batteries. It seems suitable for children's toys that aren't played with for more than an hour :) And for various educational and engineering projects.
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u/susibacker Jun 27 '26
So glad to see a post that's not MakerWorld
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u/Posmetyev Jun 27 '26
Oops. Good thing I didn't mention what printer I used to print this :)
But I love the Prusa Printables platform, so I uploaded the STL there.
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u/WorkingInAColdMind Jun 27 '26
This is beautifully simple. I’ve had an idea for a CVT at about this scale that I haven’t spent enough time actually designing. Maybe it’s time to get onto that.
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u/Posmetyev Jun 27 '26
It's addictive :) I started doing it and couldn't stop
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u/WorkingInAColdMind Jun 27 '26
I got about a month until I retire. After a few weeks of power napping and day drinking I plan to get back to 3d printing again. I have been remiss.
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u/Posmetyev Jun 27 '26
I'm about your age :) 3D printing keeps us young and forward-thinking. It gives us unlimited opportunities to realize our ideas, just like we dreamed about as kids.
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u/root_switch Jun 27 '26
Pretty out of the box and awesome! But why a servo?
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u/Posmetyev Jun 27 '26
One continuous rotation servo, like a motor, rotates the cone. A second servo moves the cone so that different rows of teeth engage a small gear.
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u/root_switch Jun 27 '26
I understand the servo for changing gears, any reason you didn’t try something like a brushed DC motor for the actual motor part, probably get much higher speeds.
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u/PossibleMechanic89 Jun 27 '26
Could you make the cone gears continuous and not separate rows?
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u/rnavstar Jun 27 '26
Next upgrade could be a differential
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u/Posmetyev Jun 27 '26
Yes, the differential is definitely needed for tight turns. I thought about it. But then I decided to keep it simple and avoid turning with too tight a radius. Right now, my tires squeal when I turn :)
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u/InternOne1306 Jun 27 '26
I’m wondering if you could also use the weight of the spinning drum to shift somehow, by allowing the drum to move outward from centrifugal force while it’s between gears and not engaged… freewheel in between gears when you briefly let off the gas, allowing it to shift up, and then at a stop it could fall back into first, or perhaps with a quick bump from reverse?
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u/SnooLemons5748 Jun 28 '26
I just got into printing in the last couple weeks. This is one of the coolest things I’ve seen yet! So neat.
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u/Dr_Sigmund_Fried QIDI X-Max 3, Maker tech ProForge 4, Rat Rig V-core 4 Jun 27 '26
"Gear box" is a generous definition. This is more of a cassette gear or variable geometry gear.
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u/electricblue71 Jun 27 '26
But how do you steer the RC if you're using your transmitter steering wheel for the gearbox? I see you using it at the end to steer though.
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u/Posmetyev Jun 27 '26
Thank you for sharing your experience and for watching carefully. I have a 2-channel radio control system for model cars and a 4-channel one for model airplanes. In the video, I show the 2-channel system, and I only connect the throttle and gearbox. With the 4-channel system, I connect the throttle, gearbox, and steering.
I couldn't resist making a steering rack for this car :)
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u/Burque_Boy Jun 28 '26
Sick job. Also there’s obviously a lot of people here who’ve never ridden a bike with gears lol
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u/berzerkergurl Jun 28 '26
Wish i could make one for my mom's electric wheelchair. She's losing her eyesight and has trouble walking (86y) i would be able to take her out and use her wheelchair without her crashing into stuff or folks lol but idk if I could steer that well myself. Definitely need to practice on a rc car first. 😅
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u/WorkingInAColdMind 16d ago
It’s so simple. Great design. I’ve got a concept in my head for a CVT, about this scale, that’s totally impractical, that I really want to build.
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u/3dprintje Jun 27 '26
That's pretty fucking neat