Designing and building a folding bike
 

Hi all,

I'm a fourth year mechanical engineering student at nottingham university over in rainy England. My major group project this this is the design and prototyping of a novel folding bike... daunting.

Our thought's are of a full size road/commuter bike that'll fold up to fit inside the 26 inch wheels, much like dom's contortion bike on youtube.

We are also looking into the prospect of hybrid electric drive. we've got a development budget of £500.

I was just looking to get your thoughts and ideas. If you had any preference to the drive mechanism, chain, shaft etc and how relevant electric power would be. The market we're aiming for is strictly commuting, maybe getting people off scooters and out of cars.

Thanks for any insight you can provide

Phil

welcome to the fold

first and foremost
to have any chance to make this a success DO NOT try to reinvent the wheel ...

STAY SIMPLE

do you have to built a prototype for 500 pounds? You better get some marketing peeps from your university to help and look and collect some extra dough ....


thor

Daunting challenge, indeed. Especially since there are some really good designs out there already. I'm thinking Strida, Brompton and Tikit.

If your target is really the commuter, then I think you should consider smaller wheels. 26" prohibits a small size. Also, commuters may like belt drive so there's no grease on their pant legs. Gotta be light so we can carry it easily. Rolls when folded. Small fold size so it doesn't take room on the train/bus. Don't need a lot of gears (maybe just 2?). Can't look geeky, or people will not want to be seen with it.

With a small development budget, you have to make sure you know your target market and set your design goals very very clearly before you begin.

Have fun.

"Novel" will be difficult. Spend a day or two looking at existing designs and you will notice a wide variety of existing variations for numerous applications. You'll see even more if you expand your search to some of the prototypes that got tiny bits of publicity.

If you want to focus on a commuter bike:

• I concur that you should go for smaller wheels. 26" is too large for a multi-modal commute or to fit the bike under a desk.
• Ditch the electric drive. It will add too much weight, cost and complexity.
• Belt drive is definitely better. For a prototype I'd just use a single speed, that will significantly reduce cost, weight, complexity.

It might help if you have some experience with building a standard bike, of course, but.... ;)

about motor
you wont be able to buy a battery for under 500 dlr ... ( a worthwhile one anyhow)

decent folders with good electric motors are upwards of 2000 dlr....

thor

Firstly, I would ditch the motor and the large wheels. Neither is necessary on a commuter bike.
Your bike will need to fold neatly, be light and of simple construction.
If you have a chain make sure that it is enclosed within the fold.
The bike should roll on one of the road wheels when folded, so that it is only carried on steps or stairways. You should not need additional trolley wheels then, and the weight is less important.
Over the years, there have been hundreds of designs of folding bike. They all have their faults. Check them out.
The perfect folding bike has not yet been invented. Perhaps it never will be, since compromise is the name of the game.
Good luck, you have real challenge here.

The biggest problem in meeting your objective of folding to wheel dia, is getting the pedals/chainring into that space. Shaft drive could be telescoped, but would be heavy and expensive. Belt drive could fold if twisted. Maybe reciprocating treadles.

What ideas do you have? What folding bikes are you familiar with? It would help us give comments.

I don't know anything about bicycle design, but I do have my experience as a folding bike commuter to draw on.

As others have noted... ditch the 26" wheels. The Contortionist doesn't even have a drive train, that is not a good example of good folding bike design. I'll be surprised if he can fit a drive train into that thing and still maintain the fold. If you think you can solve the problem more power to you, but my advice would be to go for 16" or 20" wheels.

You don't have to go with a belt drive, but it's definitely nice not to deal with grease on the train. If you go with a more traditional chain see if you can get the folding process to cover the chain some way so the grease won't be an issue.

A good commuting folder will be easy to fold and unfold (look at existing designs for inspiration), be lightweight (for easy carrying), will fold in such a way that minimizes dirt and grease getting on clothes, be rollable while folded.

Good luck... 500 isn't a lot of money for this.
--sam

How about a recumbent trike, with legs powering a big front wheel through a concentric gearbox, and a flexible seat slung between two smaller rear wheels? Picture a high-tech version of the Big Wheels toy.

http://ecx.images-amazon.com/images/...iL._SS400_.jpg

firstly, thank you all for your responses and thoughts, i am quite overwhelmed by the speed with which you have replied.

secondly, I suppose I should clear up the design brief a bit more, the idea is to design a full sized (i.e. 26 inch wheel) folding bike, it is up to us to choose the market, and I felt the commuting market was most appropriate... I guess this would be heading more toward a general purpose road machine (did someone say compromise?). The folded bike will be able to be dragged using the wheels like a trolley, maybe an extending handle like a wheelie suitcase?

The electric drive aspect is more a way of giving ourselves a better project from an employers perspective, thinking ahead, plus we figured it would be cooler to test.

Most full size folding bikes seem very clumsy and fiddly, with the exception if the swivel mode, if our design could get that level of simplicity into a smaller space envelope I'd be more than happy.

in terms of preliminary design, we're thinking single sided forks and rear arm, with a hinge in the front fork (tricky) to bring the front wheel in line with the seat and frame, and then fold this in half to get it inside the wheels, i'll get some pictures up to better illustrate this.

Hope this clears things up

Thanks again

Phil

One of the big constraints that you'll run into early on is the "foldability" of the transmission system. Most of the bikes that rely on a chain or belt drive preserve the relationship between chain ring and rear wheel: in Bromptons, the whole subassembly folds under, while in Dahons, the chassis is hinged in front of the seat post. The problem worsens with full-sized wheels. Find a way to decouple the pedaling from the driven wheel, and you'll make the fold more compact.

Electric drive is interesting, but you'll run into a range vs. weight problem. When the batteries run out, should the bike still be propelled by pedaling?

Is weight as important as folded size? Do you expect this bike to be carried?

I like your plan of making a 26" folder, there are few of these available, and those that are (Dahon, Pacific, montague) are far from perfect. They do not fold small, they need stuff taking off (Like stem and bars, front wheel etc.), or they are in short supply and have high cost.

I'd prefer as many standard parts as possible, to keep the cost down and also for ease of upgrading and maintenance. Electric power would be nice, I haven't seen any 26" folding electric bikes, but maybe have the battery (or battery and motor) removable ?.

The contortionist bike is more of a 'would like to be' dream, than an actual working bike, it has far too many joints and stuff that just wouldn't work, I guess to fit inside the wheel. I am not sure this is necessary, i'd be happy with a more rectangular suitcase size. Good luck with the project, (and degree).

I would look at the Diblasi R series. The best folding bike in my opinion for the fold aspect. If it was a lot lighter and with quality components on it I would buy one. That might no be too difficult for £500 in single speed with big apple 305 tires on. The fold is simple quick ,small, and fool proof. The luggage can be left on when folded. Its a bike with little to rival its design ,but it is over priced for the component included. It cost around £450 to £650. Therefore most people do not consider the bike ,but its very under rated as a convenient unique folder.

folding a fork ....

when I read the ideas which are floating around its gonna be another totally unrideable bike, very expensive vapourware where individual components are costing more than the whole bike is supposed to sell for.
For a non existing customer base ( excluding all commuters right from the bet )

I have the feeling that somebody is asking us for our experience but in all reality has a very clear idea what they are going for already ....
( disregarding existing patents .... IF mode folding)

sorry buddy, I dont want to come over as being ruff on ya ... just my feeling ...

if you really want to make this project work and have a small chance to ever go into production than you better listen very carefully to all the above suggestions, ie. lose the 26 inch idea ... or do you want to make them smaller in dia to achieve a small enough fold ?


Thor

Yep ... that would stop me from being a first mover. I'd wait a few years to see if everyone still had their teeth after riding the bike outside the lab.

If you have seen the IF Mode then you probably know the general lineup of folding bikes. The perfect design would ...

(1) roll well while folded
(2) fold small
(3) ride well
(4) be light enough to carry
(5) easy to cover for bringing the bike into buildings
(6) ergonomically flexible

Obviously, doing all of those things is hard. So pick which you want to satisfy well and do your best at the others. Now, I think 20" tires are perfect for a commuter folding bike. Although I realize that the public often chokes on the idea. But it is probably offers the optimal mix of the above. And the wheels are really durable too!

Personally, I would go for a Brompton-like fold with ERTO 406 wheels with simple modifications such at v-brakes, 130 mm rear drop out for regular hubs, and something more adjustable for the handlebar.

These two thoughts are both very, very true. If you take anything from this thread, take them.

Two more:

-Examine the existing market carefully. Folding bike designs come out of design schools all the time. I have the feeling that designers take on folding bike projects because all of the folding bikes currently on the market look kind of silly, and designers immediately think "I can make something cooler." But successful folding bikes look and work the way they do for very good reasons, and looking at the top-of-the-market solutions (BF Tikit, Brompton, etc) can give you a lot of insight into those reasons.

-If you're looking to make something performance-oriented, learn the true advantages and disadvantages of large and small wheels. Small wheels ride more harshly than large wheels and tend to have more rolling resistance, but are also stronger, lighter, more aerodynamic, and easier to design bike geometries around. Look carefully at bikes designed by Alex Moulton, who used short-travel suspension to minimize many of the shortcomings to small wheels while retaining their advantages. Several world records were set on Moulton bikes before they were banned by the UCI for competition. They are still being made today, but they do not fold and are relatively expensive. If you could build a folding version of a Pashley-Moulton TSR, you'd have a very, very marketable bike.

hey if your going to single side fork and rear end. You could try using MTB 20mm axle front hubs on the both wheels. Then screw a cog onto the rear wheels disc flange. Then some sort of Gearbox/freewheel at the bottom bracket.

Novel ideas:
1. A flexible frame. I've seen a video of a bike being ridden in 1930s whose frame is a spring (that's correct not "sprung", but literally made out of "slinky"). It almost certainly didn't ride like a regular bike, but from the video it still looked perfectly ridable. I've always thought a similar design would make for an interesting folding bike (perhaps a useful blend between unicycle and bicycle). Maybe you could even make it inflatable instead of just a limp slinky? See 4:53 here:
http://www.youtube.com/watch?v=jdlpJqHxLxk
2. Folding wheel. Look it up.

Combine these two ideas and I think you could make the smallest folding full sized bike ever created and perhaps even build a prototype within your budget. However, I don't think it'd be safe to equip it with a motor.

Gearing must be taken into consideration. And gearing not using a strange proprietary mechanism where only one manufacturer sources this.

one sided hinged fork sounds like a recipe for disaster.

if you are looking at a template for a full-size folding bike, the montague folders aren't a bad start.

26" inch? why...you guys NEED to research a bit more about rolling resistance...16" wheels can be as fast as a 700c with the same effort, but with less inercia, more acceleration...

moulton spent big part of his life trying to make a non traditional bike
brompton seems to have spent most his life trying to perfect the folding design
bike friday
dahon
...im a noob here, but you guys should be looking into the history of foldables, THEN, ,make your "own" design.

im sure anyone can imagine how to fold a bike up..but making a foldable that actually folds and performs is on another level...imagine all the torque and abuse a bike is involved in..now imagine a folder that would fold while riding...ouch!

I use a 26 folding bike for commuting, it doesn't get folded very often but it rides over rough cobbles very well. I wouldn't like to take it on a crowded commuter train.
One-sided stays are used on motorbikes and have been used on a few bikes, esp by Giant and Cannondale. They work well and can solve the width issue of a folder.
Most folders have complex shapes made from welding lots of complex bits of metal. Seems like a suitable application for carbon fibre.
Chains have very few advantages over modern belt-drives for the type of riding done by mixed-mode commuters. The recent world record circumnavigation of the glove was done using a Gates drive Rohloff system. You could sue a lighter 3-speed or singlespeed.

There is no perfect folder, the design contraints are too many and too varied, compared to single purpose sporting bikes

Don't underestimate how difficult it will be to create a workable transmission that will quickly and repeatedly fold in half between the bottom bracket and drive axle. If the bike must fold to within the wheel diameter that is issue #1. Do nothing else until that issue is solved.

The contortion bike is a joke because they solved the problem by saying "then magic happens".

The only way I can think to do it would be a friction drive, but then you have major issues with gear reduction, tread wear, performance in the rain, etc.

A well designed belt drive folder with 16 or 20 inch wheels would fold smaller and work better than a 26" folder that sacrifices function for fancy appearance.

Integrating a telescoping handle is a good idea.