Crazy Bike Fab

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The assignment here is to build something you can ride that isn’t like a normal bicycle.

Project requirements

As with many projects, it’s important for the instructors to try it out themselves before implementing it in a class. Make a few creative bicycles in your spare time and ride them around school. They make great advertisements for the project and help kids realize what’s possible.

I like to run this project with two requirements: you must make something you can ride, and it can’t be much like a normal bicycle. For the first iteration of the project you might restrict students to using no more than two wheels, or at least to use only one driven wheel. Inevitably some students will want to make a four-wheeled car sort of vehicle, which is a good deal more complex because bicycle drive systems (chains and sprockets) are designed to power a single wheel.

A second iteration of the project, or a more advanced version run with experienced students, might choose a particular design challenge- to design a bike for disabled users, seniors, or users that need to carry groceries and live in walk-up apartments, for instance.

As with most of our design/maker projects, we try and incorporate some form of public display at the end. This adds motivation for the kids and is good publicity to boot. The first year we did this project we rode the machines across the soccer field with most of the school watching. The second year they were incorporated into our annual kinetic sculpture race. Either way, it gives kids something to look forward to.

Learning goals

As with the Kinetic Sculpture Race project, lots of skills are involved. Students learn to weld (a tremendously empowering skill), work with steel, and solve mechanical problems, They also practice real design – brainstorming, planning, sketching, prototyping, testing, failing, and iterating. Nearly all entrants run into obstacles that require rethinking and redoing at least parts of their projects. The most important things they learn, in my opinion, are (1) patience, and (2) that with patience and determination one can accomplish great, improbable things.

Introducing the project

I usually start with a slideshow to get an idea of what other folks have done. You can get some fun images by googling “kinetic sculpture race”. The international human powered vehicle association is a good source too:  Chunk 666 is an inspiring group, but you might vet their text before throwing it up on a screen: Books on bicycle history (Bikes & Trikes of Long Ago, 1989, Chandler Press) and Bike Cult, by David Perry among them) illustrate some of the fascinating and crazy bicycle contraptions invented earlier this century. Encycleopedia, published annually in Britain by Open Road Ltd., is a compendium of cutting edge creations.

Depending on the kids’ level of familiarity with bicycles, it can be useful to go over how bicycles actually work. One way to do this is fill a box with bike parts and have each student take one and figure out what it does, how it works, and explain it to the class. It’s interesting to discuss other mechanical ways to achieve the same functionality – what’s an alternative to a bike chain? (belts, gears). Besides using handlebars, how else could you steer? It’s worth taking a close look at how bike wheel axles work- the axles themselves are stationary, with the bearings in the wheels. This is one reason that it’s tricky to make bikes with more than one driven wheel – the parts needed have a driven axle that turns two wheels (like the ways cars work) aren’t standard. Another useful thing to look at is the rake angle of front forks (the angle of the invisible line that runs through the front wheel axle and the head tube. This is pretty standard on bicycles (about 73 degrees) – why? See if the kids can figure out what happens if you modify the angle. Have them think about swiveling supermarket cart wheels (which have a trailing rake, and follow the cart) vs a forward rake. The bottom line is that pushing the front wheel too far out in front (i.e. insane chopper style) will make the bike hard to steer, as the front wheel can just flop over, while moving the front wheel too far backwards will give you a bike with a mind of its own.

Before design begins it’s a good idea to demonstrate a few of the tools, particularly the tubing notcher, so kids can see what’s possible with steel tubing. This might be a good time to talk about weight loads and stresses on a bike frame and the utility (and ubiquity) of triangles in structural design, from bike frames to bridges.

The design process

It’s useful to examine the way bicycles are used in other cultures, particularly in parts of Asia, where they are (or were) often a principal mode of transportation and way to move cargo. We watched a slide show from a friend who had spent time in Vietnam. One interesting aspect of bicycles as a design project is that there’s so much room for improvement. The design of nearly all bicycles produced today hasn’t changed much since high wheelers went out of style around the turn of the century. And yet, if you question the design of today’s bicycles, numerous flaws are apparent: the rider’s back is bent over, weight is on the wrists, and in an accident, the foremost part of the rider’s body is the head. It almost seems that bicycles haven’t changed because no one has thought to question their design. (Of course, there are lots of people questioning bicycle design, it’s just that most of them haven’t made it into large-scale production yet.) These ideas might prompt a discussion on how many other products could be redesigned, and how anybody can have a great idea.

Our design process loosely follows the iterative design thinking blueprint- brainstorm, improve, sketch/model, repeat. The first drawing exercise was to sketch, whatever size you liked, the bicycle you wanted to build. The sketches ranged from basic to fantastic. Each student explained his or her machine to the class. After each presentation we discussed the feasibility of the bicycle- would it work? Why or why not? If not, how could the design be changed? Could we build it with the tools and materials we had? Which ones? Most of the designs were modified through this group process.

If your students are new to design, it might make sense to use a hands-on approach to making scale drawings. This means drawing them life-size (1:1) and tracing actual pieces of tubing and pieces of scrap bicycles, such as bottom brackets and rear triangles (difficult to make, easy to find) onto big sheets of paper taped to the floor. Once the design is on paper it’s easy to measure and note angles and verify tube lengths. Making scale models out of wooden skewers, tape, and cardboard can be helpful too, especially if you incorporate human figures. This is the right time to spot designs that won’t work at all due to lack of pedal clearance, no room for knees, etc.

First-time bike builders will often sketch great ideas without much thought as to how the bike will work mechanically. For most students I recommend (or insist) that they use an existing rear triangle / bottom bracket and pedals combination – why not take advantage of all that free, time-tested design to make your bike move? It’s fine to move the bottom bracket to another location and extend the chain though.

By this point many students will be enthusiastic and impatient to finish their machines and begin terrorizing the neighborhood. It can be a bit of a letdown for them to realize that building a bicycle of any kind is a long process, usually marked by mistakes that take time to sort out. Welding is quick, grinding off a welding mistake, or a bad weld, isn’t. This is a good time to emphasize patience. I’ve found that making tidiness in the shop part of the project grade is helpful too – it’s all too easy to be so focused on one’s project that suddenly it’s time to rush to the next class, leaving a pile of tools, parts, and supplies strewn about, which slows everyone down.

As with any extended project, regular group check-ins are helpful, both to spread the momentum around and to give kids a chance to make suggestions to each other on their projects. Hopefully by this time the public demonstration has been scheduled so there’s a date to work towards.

The bicycle design project stresses several key elements of design: the importance of planning (sketching, drawing, measuring, testing) before building, the value of getting input from others and working together, and that the work can be fun. Like many design projects, It also helped to put math and other academic subjects in a different light, encouraging students to see these disciplines as tools they can use to do what they want. Ideally students will discover confidence in themselves that wasn’t there before- the feeling that they are designers, and that with enough effort and planning, they can create anything they put their hands to.

Materials and tools:

Space. You’ll need storage space for scrap bikes and parts and the projects themselves. Both can be outdoors. We found it useful to maintain a small bike scrapyard that kids could pick through to find parts. Your workshop will need to be ready for welding, which means some kind of ventilation and hopefully a concrete floor. Bins or cubbies for individual students or teams work really well for this project, as students may need small specialized parts for their projects. Having to go hunt in the scrapyard again for that exact sprocket because you lost it is a real time-waster.

Old bicycles and parts in any condition.Bike shops usually have a corner somewhere filled with dead frames and parts that they are willing to donate. Apartment building supervisors are a good source too, especially near universities. Students and other tenants often abandon bicycles in these buildings’ basements and bicycle lockers. I didn’t have any luck with NYPD but your local police department might be worth a try. An email to parents can generate a lot of bike donations too.

Stripping the bikes and sorting the parts is a real time-saver. We used 5-gallon plastic buckets for brakes, derailleurs, chains, stems, etc.

Shop tools. With a few exceptions, I usually choose inexpensive tools from Harbor Freight  for school projects. They tend to work well enough and cost a fraction of what better brands cost.

Bike tool set and a good tire pump. We used the Nashbar Essential Bike Tool kit, which costs $50.

You’ll need a few new bike parts: tires, tubes, brake pads, shift and brake cables and housing, bicycle grease. This stuff is all available online. Bike Nashbar is a good source. I found bulk bike helmets for about $10 each at

Steel tubing. The last time we ran this project we tried something new: standardizing on 1″ square tubing in two thicknesses, 16 gauge and 14 gauge. The advantage of square tubing is that since the sides are flat, you don’t need to make round miter cuts to join it at angles. If you need to mate it with round tubing on a bike frame, you can cut the end with a hole saw on a drill press.


You don’t need a notcher (shown here) to notch square tubing – you can just use a drill press and a hole saw (the yellow part)

If working with round tubing, you’ll need a Tubing Notcher. This connects to your drill press to make mitered (scooped out) cuts in tubing, so the tubes fit together nicely for welding. The Harbor Freight model costs about $50. You’ll need a set of hole saws as well.

Drill press. Needed for the tubing notcher and useful for working with steel in general. Harbor Freight models are good enough. You’ll want to get a good set of drill bits too.

Chopsaw. The $100 harbor freight model is good enough.


A cheap chopsaw with an abrasive blade cuts tubing nicely

Mig welder. In my experience it makes sense to get a good one – not Harbor Freight. Miller, Lincoln, and Hobart all make quality welders. Expect to spend some money on this, perhaps $1000 or more. Personally I like the Lincoln Multimatic 200. Get extra welding tips from the manufacturer. I’ve had good results from Harbor Freight Mig wire though. Harbor freight welding jig magnets are also super useful.

Hand grinder. You’ll probably want two of these. Set one up with a grinding wheel, the other with a cutting wheel. They run about $15 at Harbor Freight. If you buy them there, get a few extras.

Safety gear
. Goggles, welding masks, gloves, and jackets. It’s worth it to get at least two auto-darkening welding masks, they are much easier to use than the older flip-down kind. The Harbor Freight varieties are good enough.

Square tubing is easy to work with – these mitered cuts were made with a chopsaw


A few gotchas:

Left-size pedals are threaded backwards

Wheel nuts, particularly on older bikes, come in a wide array of diameters and threads. Keep wheel nuts threaded onto wheel axles so they don’t get mixed up.

When separating bike chain, use the chain link extractor tool to push the link pin almost all the way out, but don’t go so far so that it pops off the chain. They are very hard to get back in.

Kids are often so excited to ride their creations that they don’t think about protruding sharp edges and other hazards. A safety check before launch is recommended, as are helmets.




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