Objective: To design the lightest, most portable folding bicycle in the world
Problem: Bicycles are a very popular form of short-distance transportation. In places like the Bay Area, its almost a way of life. Its easy to see why. Bicycles have unlimited range (depending on how fit the rider is), don't need much maintenance, and are fairly affordable. Plus its amazing exercise.
However, I believe the bicycle is losing its allure in an urban setting. Today's cities are much more congested and densely-packed than cities were when the bicycle was invented back in the late 1800's. The bicycle is slowly becoming more and more unfit to be ridden in major cities.
Today's cities require a vehicle that is much smaller (around the size of a kick scooter), very light (so it can easily be carried when not being used) and stylish (to cater to style-conscious urbanites). The natural question at this point is, why not folding bikes then? Don't they fit the bill?
Folding bikes today are well built and yield great performance. However, they have a huge drawback. They don't fold easily. There are anywhere from 5-8 distinct folding actions, which greatly diminishes the value of having a folding bike. Faced with this situation, most people that were observed simply didn't bother folding it up as it was just too cumbersome to do so.
Major Considerations:
1) Has to be lighter than 15 lbs
2) As portable as an adult kick scooter when folded
3) As fast as a fixie (15mph) at normal cadence
4) Must only have two major folding actions or less
Solution: Zippy is an entire rethinking of what a bicycle is and should be. It evolved organically, without a static template of what the final result has to be.
This is why I made the decision early on to get rid of the seat. Zippy is intended to be used for distances under 3 miles. For these distances, a person wouldn't have an issue standing up. Not having a seat also meant increased portability.
A new prototype was created weekly and shown to a select number of people who had expressed interest in the product. Darwinian natural selection was rigorously followed: the features and attributes that the users loved were maintained and improved upon, while the ones that were the subject of disdain or indifference were weeded out. This method was adopted to ensure product market fit.
Problem: Bicycles are a very popular form of short-distance transportation. In places like the Bay Area, its almost a way of life. Its easy to see why. Bicycles have unlimited range (depending on how fit the rider is), don't need much maintenance, and are fairly affordable. Plus its amazing exercise.
However, I believe the bicycle is losing its allure in an urban setting. Today's cities are much more congested and densely-packed than cities were when the bicycle was invented back in the late 1800's. The bicycle is slowly becoming more and more unfit to be ridden in major cities.
Today's cities require a vehicle that is much smaller (around the size of a kick scooter), very light (so it can easily be carried when not being used) and stylish (to cater to style-conscious urbanites). The natural question at this point is, why not folding bikes then? Don't they fit the bill?
Folding bikes today are well built and yield great performance. However, they have a huge drawback. They don't fold easily. There are anywhere from 5-8 distinct folding actions, which greatly diminishes the value of having a folding bike. Faced with this situation, most people that were observed simply didn't bother folding it up as it was just too cumbersome to do so.
Major Considerations:
1) Has to be lighter than 15 lbs
2) As portable as an adult kick scooter when folded
3) As fast as a fixie (15mph) at normal cadence
4) Must only have two major folding actions or less
Solution: Zippy is an entire rethinking of what a bicycle is and should be. It evolved organically, without a static template of what the final result has to be.
This is why I made the decision early on to get rid of the seat. Zippy is intended to be used for distances under 3 miles. For these distances, a person wouldn't have an issue standing up. Not having a seat also meant increased portability.
A new prototype was created weekly and shown to a select number of people who had expressed interest in the product. Darwinian natural selection was rigorously followed: the features and attributes that the users loved were maintained and improved upon, while the ones that were the subject of disdain or indifference were weeded out. This method was adopted to ensure product market fit.
Design Process
Shows the very first design of Zippy (without a handle). As can be seen, it is purely functional and not very pleasing to the eye. It requires the user to pedal like an elliptical trainer. This method of propulsion was chosen as it is closest to normal walking motion
A to-scale CAD model of a 6'2" man riding Zippy
The designs above were still unsatisfactory. The prototypes that were built based on these designs (shown in the fabrication section below) were more than 20lbs.
This meant another minor redesign. So, the central chassis structure was curved up instead, as can be seen on the extreme left below: |
An improved design shifted the guide rail to the middle (enclosed by the central bar)
A close-up of Zippy as it is being ridden
However, it was soon obvious that the elliptical motion design was nearing the end of its line. When tested with users, most preferred the normal biking motion. So, the decision to discard this method was taken. The sketches below show some designs for the new chassis structure.
|
A redesigned Zippy
|
|
|
The design eventually evolved into this
Fabrication and Assembly
Zippy's fabrication required the use of some complex industrial equipment and tools. It was entirely manufactured at TechShop San Jose. The tools included, but were not limited to:
|
1) Tormach CNC router
2) Shopbot CNC router 3) Vacuum former 4) TIG welder 5) Sandblaster 6) Drill press |
7) Metal lathe
8) Vertical bandsaw 9) Cold saw 10) Spray paint 11) English wheel 12) Powder coater |
The very first version of Zippy
|
Side view of Zippy
The video below shows me riding the first working version of Zippy
|
The version above was mainly a way to test how the system worked. So it was made entirely of AISI 1018 steel. This is highly weldable and machinable so was an ideal material for prototyping purposes. However, it is a lot heavier than something like chromoly steel or aluminum so it is not suited for the production version. Since the results were satisfactory, an all-aluminum (6061-T6) version was made, as shown below.
Zippy v.4
|
Zippy v.2 on right with v.3 on left
Zippy v.5
|
All the versions shown above had subtle differences between them. They were iterated based on the comments of users. Version 2 (v.2) had very stiff skateboard trucks, so it didn't steer very well. They were subsequently replaced by looser, wider trucks in v.3. Users would also slip out of the foot rest even though tread plates were installed. To mitigate this, a layer of grip tape was added.
One major addition that can't be seen is the freewheel in v.5. This allowed for coasting and much better control. The weight was still a huge concern as v.5 weighed in at a hefty 22 lbs. This was a wake up call and forced a rethink of the entire design. Hence, v.6 was designed, as can be seen below:
One major addition that can't be seen is the freewheel in v.5. This allowed for coasting and much better control. The weight was still a huge concern as v.5 weighed in at a hefty 22 lbs. This was a wake up call and forced a rethink of the entire design. Hence, v.6 was designed, as can be seen below:
Zippy v.6 had a much slimmer, simpler design. It inherited its elliptical motion from earlier versions
|
v.7 got rid of the elliptical motion and went with standard bicycle pedaling motion
|
The elliptical motion which was chosen for its similarity with walking motion was at last, discarded. Although some users did like it, it was found that the majority were indifferent. Because riding a bicycle is such a universal activity, its pedaling motion has become almost second nature to most people. The hypothesis that people would like a motion that was similar to walking was incorrect.
So Zippy v.7 went back to basics and adopted the bicycle's pedaling motion. An added advantage was the drastic reduction in weight. It was now at 17 lbs, only 2 lbs short of the goal.
The series of pictures below show a novel locking mechanism developed to ease Zippy's foldability. Every folding bike in the market has cumbersome, multi-step locking and unlocking mechanisms. Due to this, most folding bike users don't even bother folding it up most of the time. The idea is that if folding took little to no time, the value proposition of such a bike would skyrocket.
A sub-$10 door lock was used to design this contraption. In order to go from folded mode to being ride-ready, the user merely has to pull on the handle bar. It would just snap into place and be ready to go. To get rid of any rattle or play that might develop, a rubber suspension was added between the two mating plates.
So Zippy v.7 went back to basics and adopted the bicycle's pedaling motion. An added advantage was the drastic reduction in weight. It was now at 17 lbs, only 2 lbs short of the goal.
The series of pictures below show a novel locking mechanism developed to ease Zippy's foldability. Every folding bike in the market has cumbersome, multi-step locking and unlocking mechanisms. Due to this, most folding bike users don't even bother folding it up most of the time. The idea is that if folding took little to no time, the value proposition of such a bike would skyrocket.
A sub-$10 door lock was used to design this contraption. In order to go from folded mode to being ride-ready, the user merely has to pull on the handle bar. It would just snap into place and be ready to go. To get rid of any rattle or play that might develop, a rubber suspension was added between the two mating plates.
|
|
|
Zippy hanging on a VTA light rail bike rack. As can be seen, its roughly half the size of a normal bicycle.
|
Zippy is small to be kept in the bus without drawing the driver's ire
|
In order to hit the 15 lbs mark, the chassis had to be redesigned. So instead of going with the conventional wisdom of round tubes (as with bikes), experiments were done with a sheet metal design. It eventually gave way to the final design as shown below. It weighed just north of 15 lbs.
The aluminum sheet metal chassis design. The tubes down the middle ensure its stiffness
|
Zippy v.8
|
Credits: S.G.M. Hossain, Lee Rajkhowa