How can I make a giant bike cog like this one?

Here's a site with  the inspiring article: 

Anyways, I want one. First of all I would suppose I'd need a pattern. What program would you suggest I used to make a pattern?  A solid circle of metal with teeth on it will do. I'm thinking of gluing a pattern to a piece of metal, cutting it out as best I can with a grinder then going bike to clean it up with a tungsten carbdide dremel bit. I gues it could be a few thinner sheets of metal that could be  spot welded together. I dont have any tech shops/idea foundries in my town. I say that because I'm wondering could I just create some type of file that a mill machine could read and cut it out for me? I have a couple different reasons for wanting a larger cog, the practical one being I want a cog large enough that the pedals would be moving around very slowly so you could just shift your weiht back and forth, more falling with your body weight than pedaling. The 2nd reason, more lofty and long term goalish is if you can get this much power from a bike, to propel it 100 mph, it just seems reasonable that a human powered aircraft is within reach, as in attatch a hang glider to a bike and have the pedaling able power a propeller once airborne. Anyways, how would you go about making a giant cog?

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Burf3 years ago

I doubt you're going to be able to do an adequate job with a file and rotary grinder. Find a machine shop with a water jet cutter and give them the specs and they will make you what you need with precision and accuracy. If you can't find a shop locally, contact one by phone or email, give them the specs and you get it cut and shipped to you.

+1 on the waterjetting, or even lasercutting.

nathanaloysiusbash (author)  Burf3 years ago

Yea. Makes sense. I will do that. Assuming my stick-to-it-tiveness holds out long enough for me to learn cad and design the gear and I can afford the price of having it made and shipped.

rickharris3 years ago

Free gear template generator to get you started.

nathanaloysiusbash (author)  rickharris3 years ago

I downloaded that but couldn't quite figure out which parameters to adjust to make a bike gear.

play around a while - that's learning

I would point out that such a high gear ratio is totally useless and it needs a LOT of energy to get up to 100 MPH. Usually they start off towed behind a car until they are going fast enough to be able peddle.


I am not sure where you are based but from the UK we have access to a series called Speed with Guy Martin ; in one episode he builds and rides a bike to break the speed record; in another series he builds a flying bike that breaks the world speed record.

The way they are built and the problems that they encounter are all shown; it is a fantastic show.

Good luck


Kiteman3 years ago

As others have pointed out, you are not going to get 100mph out of a 100mph bike.

You need a car to tow you up to speed, then to provide a wind-shield to allow you to slip-stream. Also, the 100mph cyclists are professionals - they've spent years training to build up the strength and stamina for the event.

To further add to this pile of negativity, using a metal gear will not help you achieve human-powered flight. If you look at the technology used to achieve powered flight, it is light - no metals, all high-spec polymer films and composites, only just strong enough to support the pilot, too fragile to be outdoors in more than a light breeze.

If you look at the Sikorsky prize-winning helicopter, the large gear was only shifting the tiny mass of the rotor blades, and even then it wasn't running a drive-train, it was unwinding string wrapped around the rotor shafts, restricting flight to just seconds.

If you're going to try for human-powered flight, look to the entrants of the Icarus Cup, who are working to establish an annual, international event for human-powered flight.

If you really want to see the capabilities of human powered flight then look up the Red Bull Flugtag. It's a compensation of human powered flying machines.

Get on a CAD program that is able to do gears and you can print a paper diagram of any size gear you want. But the larger the gear is the thicker it needs to be to maintain it's shape. Otherwise it will warp with the strain of peddling. Weight will be an issue.

Just know it's not as simple to get that bike moving as your are thinking. You can gear a bike up so that a quarter turn of the peddles will give you 10 or more on the wheel. But it becomes impossible to peddle under your own power/weight.

That red bull stuff is funny. You do know that human powered flight is real though and has been done before. Google 'human powered flight' and look at the video results. The first few hits are real examples of human powered flight. As to the CAD program it seems there are some free cad programs out there. Thanks for the tip. Now I just need to learn how to use one of them.