The bicycle is an invention that has not changed in its fundamentals since the first recognisably modern machines appeared in the closing years of the 19th century. Its frame uses a structure of two triangles, its wheels are equal in size, and it’s propelled by a pedal crank and (in most cases) a chain. Bicycles have improved vastly in materials and performance, but if you were to wheel a 2026 tourer into an 1886 bike shop, the Victorian proprietor would recognise it. Only a very brave engineer would try to fundamentally change such a formula, but here’s [Not programming] with a crankless bicycle.
The idea is to replace the crank’s circular motion with a linear one, thus providing a more constant propulsion. The build was inspired by another that used a sinusoidal track in a rotating cylinder to achieve the necessary conversion. This design takes a different tack, using an arrangement of gears and freewheels he describes as a mechanical rectifier to convert the back-and-forth motion of pedaling into rotation. The pedals themselves are stirrups mounted at each end of a V-belt.
This build is an exercise in pushing the limits of 3D print strength, as prototype after prototype shears under load. He does finally get the thing to work, though, and we admire his persistence. Oddly, this isn’t the first 3D-printed bicycle geartrain we’ve seen.
There have been oval sprockets designed to keep the torque advantage of the crank more linear, an admirable compromise.
Shimano BioPace, around since the ’80s. My previous craigslist beater bike had it and it was an unexpected treat. It gets “bigger” when your pedals are at the top and bottom position, to prevent your road speed from dipping at that moment in the cycle when your feet naturally slow down. And allegedly it reduces pain in your knee because that moment when the knee reverses direction now happens slower.
Interestingly, modern oval gears have chosen the opposite strategy: they are smaller when the pedals are at top and bottom, on the theory that you have very little leg power there so you should get past it as quickly as possible, knee comfort be damned.
Back in the 80s when Biopace was a thing, I made an oval chainring for my bike by splitting a circular chain ring and separating the two halves with a couple aluminum plates. I did all this with hand tools. I put it on my hypercycle recumbent bike and rode it from Tecate to Ensenada, about 75 miles, and it felt like going up stairs the whole ride. There’s a photo of the chain ring here: https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhq2izbAMQ7AT0QyZQqUSB3ymd_ZC47-f1N8ODczzTHklere_UROn3My2HmBeCvNTTAtOHoAUw6OCyGAFtMdvGJeuSoX1-nBFf13QbwOkmFvm2KCU6v7MSqweKqJcS-a08jBr2b979v611_/s1600/mark_pace.jpg
Crazy
You can see the system @08:35.
It’s quite silly. Instead of just using a chain (or timing belt in this case), he added extra 90 degree pinion gears, and another belt to the transmission. By adding all this stuff, and then still needing the gear hub in the back wheel, makes it heavy, expensive and low efficiency.
In day’s long gone by I’ve seen some clever systems which uses curve disks and cords to transmit the pedaling forces to the rear wheel, and “gear” selection (force to torque ratio) could be adjusted by moving the curve disks. That worked quite neat and probably had a good efficiency too. The main disadvantage is that the cords were consumables and had to be replaced quite often (Stringbike below clamied 1000 to 2000km for string replacement). I don’t know what the “official” strings costed, but bare UHMWPE is not expensive these days. You should be able to replace the strings a few times for the cost of a single chain.
After a bit of searching “Stringdrive” was one of the systems based on cords that made it into commercial production. The wikipedia article does not have much info, but the other link has a review with pro’s and con’s of this system.
https://en.wikipedia.org/wiki/Stringbike
https://www.cyclingabout.com/are-chainless-string-drive-bicycles-a-genius-or-terrible-idea/
With both a rotating axle, the extra curve disks and all the pulleys it does look more complicated then it should be, and that also reduces efficiency. The really hard part is to think of a simpler system, without making it heavier, bulkier, or giving up the “gear” ratio and “pedal cadence” optimization.
Not to be negativistic, but this site is a great example of how to bork up even image loading by doing the required-quality check yourself in JS (hint: that’s a ages-old built-in feature of webbrowsers).
Yep I remember this drive
First, I have to say “love it”. I’m up to about my 6th silly project that’s mostly comprised of me finding out how much I don’t know about something!
I’m currently working on two bike projects and now in my third year of discovery!
I can happily say, I’ve figured out some of the fundamental problems and am slowly working my way to a commercial product.
I can say, with some experience, what your up against. 5 million plus patents for one. I just mention this because the bike seems to be one of those go to for budding engineers that think “Oh I can improve that part”. You’re up against a hundred years of bike technology, and some of the fundamental technologies were borne thousands of years ago. Add thousands of people/engineers trying to improve every component, fundamentally, and functionally. Not that I think you’re in trying to reinvent the wheel (if you are, my hats off to you;)
I’ve been racing bikes since I was a kid, even raced as a processor some years, so I know a little about bikes!
As mentioned in previous comments, biopace and osometric chain rings were an attempt to improve both power output and efficency. Both came up short because the efficiencies were based on mechanical principals, with little regard for biomechamical factors. Biopace was abandoned early on, because they figured out the rate of fatigue for the rider increased dramatically over distance. One reason for this is that you’re legs aren’t really built for pedalling. The muscles are in a constant transitional phase from the rotation of the pedals. It certainly doesn’t allow you to produce maximum potential wattage but that smooth transition, allows the fatigue load to be spread over a lot of muscles, allowing riders to ride efficiently, for long distances.
I hope you continue this development, so I can learn a few more things, and also, for the amusement factor;)
One fundamental thing i can tell you, without getting too deep into the design. It won’t work, as long as your ankles are “swinging”. Your ankles have to be stabilised before you can produce any meaningful power, especially on a bike, as it’s in a constant phase of controlled “falling sideways”! Your current “stirrup” had to become a stabilised lever (pedal). So some kind of slotted lever mechanism is necessary.
I’m looking forward to seeing where you take this……
Some people should be banned from owning a 3d printer
What is he even doing to get such horrible prints? He mentions 2 layer walls, which is insane…
A heads-up, in case he’s reading the comments: If you have the belt’s model number, you can usually look for commercial pulleys for that belt and download a CAD model of it. A few days ago I printed a XL belt pulley for an old food processor, with minimal changes to the shaft, and the teeth meshed perfectly with the belt. That way you don’t have to spend half a kg of filament on tests as he did.
He made least a few classic 3D printing mistakes- designing the printed plastic parts as if they were metal- i.e. too thin for the forces that will be applied. 3D prints get strength from bulk plastic. If you design a part like it’s made of metal, it’s going to fail quickly. 2 line walls? That’s barely enough for something that doesn’t have any forces applied. I’d bet a dollar that he used gyroid infill, too.
Back when people used to use 3D printed parts to build 3D printers I saw the same problems. They’d print motor mounts like L brackets because that’s how metal motor mounts are made. Of course they’d twist under belt tension. And they’d print them using PLA, and the motor would heat up and the mount soften and warp.
IMHO it’s all part of the learning process. Most people who seriously dabble in 3D printing are neither mechanical nor structural engineers. I try and give people a pass for those details when their interests are aimed at non-mech/struct interests or learning themselves through trial and error. Part of the fun of being a hacker/maker is learning to stumble around a bit.
Totally agree. +++
It is a great learning exercise, other that that it’s a terrible concept – why all the 90 degree changes in motion and the unnecessary gears? – with incrementally less terrible execution, but that’s fine.
Springs to bring the pedals to the top would help, a sprague clutch on each crank where it attaches to the shaft would be simpler.
I have no idea what the advantage it this or a cable or conecting rod drive is, except possibly for one legged cyclists. Otherwise having your legs synchronized and the peddle returning to the top is a good thing, not a problem.
But as a learning exercise it is excellent.
I seen those horse stirrups flopping around and I say no thanks, I’ll stick with a standard bixyxle
It really doesn’t take a rocket scientist. Just one small push and he could eliminate 95% of the torque.
Is there any reason to aim for a purely vertical motion? It’s adding a lot of complexity so unless there is an advantage this is only interesting as a purely academical exercise.
Right? The pedal does the linear to circular conversion in simple already.
Test the bike on a trainer not on the road.
All for trying new things, but it looks like a way-over complicated version of the Star Ordinary bicycle ratchet drives- actually giving two gear sets. Also would’ve been easier to adapt, more practical. But wouldn’t have been “new” I suppose.
Cool concept to ponder but this design is creating an overabundance of frictional losses.
Need simplification…you replacing 1 chain for all this …
Will this revolutionize the bicycle drivetrain…probably not…but this was a great lesson in curiosity, creativity and perseverance. Kudos to you.
Uh, look, as cool as 3D rinting is, plastic is not suitable for every usecase. Especially not for significant forces.
Vertical pedals get re-invented about every decade. Here’s one from a decade ago that is also electric for some reason: https://www.youtube.com/watch?v=qlZKAra1tbQ
I am always amazed at the non-problems inventors (and industry) are always fixing with bicycles. Bicycles are an INCREDIBLY optimized machine, and most changes at this point are more about the money to be made than the improvements to be had.
As a for-instance, rim brakes versus disc brakes. Disc brakes have undeniable advantages! But a 22lb bicycle is not a 400lb motorcycle or a 4000lb car, and bicycle tires have a tiny tiny fraction of the contact patch of those vehicles, so most of the advantages of disc brakes is just wasted on a bicycle.
I’m not a socialist so I’m not going to prevent you from enjoying your classic steel-framed single-speed bicycle with rim brakes and whatnot. However, I love my 2025 hardtail MTB more than any other bike I had before.
I’d say that mid 2020s consumer-grade MTB (which, compared to entry-level bicycle-shaped-object from Walmart, already has quality parts fitted; yet no fancy crap like carbon frames for those cyclists with infinite money cheat enabled) really feels like bicycle formula perfected. Finally it’s all simple and logical construction with as few parts as possible. It’s like finally it was designed by somewhat sane people and engineers instead of still refining hacks and design choices from the 1920s.
• Thru-axles ❤ – a single metal rod instead of quick-release system which had lever, nut to adjust, lawyer tabs, conical springs.
• Disc brakes ❤ – will work for years without maintenance as the system is self-adjusting and weather-resistant. The only work needed is a 5-minute brake pad change.
• Cables routed through the frame ❤ – makes cleaning the frame from mud and grime a simple task.
• 1×12 gearing ❤ – finally no more fiddling with this f**king front derailleur. Finally no more incidents where this stupid plastic shield on the crank gets broken and your jeans pants get chewed by chain and sprocket.
• Drop post ❤ – easily adjusted if going gets rough (or when you need to put the thing in the boot of your car)
• Tubeless tires ❤ – recently I came home and discovered I had the misfortune of driving over some wood staple left behind by road workers making a temporary fence. Instead of fitting another tube I just went for a short ride on the next day and the thing sealed itself shut. Lovely thing.
• Standardized (machine) bearings in wheel hubs ❤ – no more screwing around with those stupid adjustable nuts, bearing balls and grease everywhere.
Compared to my 2018 (and earlier) MTBs I can finally take the thing apart down to a bare frame and put it back together in an afternoon without needing a doctorate in birotology to make it work again.
12 wide?
How skinny is that chain?
Ratio range?
I’d expect to lose more on the rear derailleur than you gain from losing the front one.
I’d restate Duane’s point and call out TFA.
It does not take a ‘very brave engineer’ to think they can ‘fix’ bikes.
Different adj…
Disc brakes are an optional fine tune for most.
Not any sort of fundamental redesign…no H shaped shift pattern and shaft drive.
A status symbol for some.
Most tour de frog LARPers have moved onto CF frames and seats that play with their balls as they pedal.
I digress.
As a bicyclist in the rainy Pacific Northwest, you can pry my disk brakes from my cold, dead, inevitably wet hands. I’m not going back to rim brakes.
Totally pointless; conventional bicycles are a magnificent form of transportation, simple, efficient and reliable. This is just a solution in search of a problem to solve
And what happened to – quite relevant – comment about shimano BP?
“…replace the crank’s circular motion with a linear one, thus providing a more constant propulsion…”
How is linear movement continuous and circular motion not?
Any cyclist knows that constant propulsion is easily achievable using pedals.
The solution is toe clips, or the awkwardly named “clipless” pedals.
Clips/clipless pedals let the rider push the pedal down AND pull it back up(and the in-between parts too).
This is why cyclists use them. You can use more muscle groups while riding, which can be used to rest one group while the other takes over (pull only to let push muscles rest), or augment the force of one group with the other for a lower individual load or higher maximum output (pull with right while push wih left).
NOTE:
“Toe-Clips” are a strap, or cage with a strap, that your shoe slides into and is sinched tight to attach the shoe to the pedals.
“Clipless pedals” are a system of pedal and shoe mounted clip which attaches the sole of the shoes to the pedals.
Despite this connection being MUCH more solid, clipless is safer and more convenient (during riding) because they can be released with a practiced movement by the rider, unlike toe-clips which must have the straps released by hand. One cannot ‘bail out’ of toe-clips, including when a rider simply comes to a stop.