DESIGN AND INNOVATION : THE BROMPTON FOLDING BICYCLE
1. REPRISE : CONCEPT TO PROTOTYPE TO PRODUCTION
Go to buy any functional product, and you will almost certainly be presented with a range of different designs. Some of the differences will just be in the styling, but there may also be real differences in function or quality, which may be reflected in the price. Different design concepts lead to competing products with particular sets of advantages and disadvantages. Moving from concept to production depends critically on the industrial and social context. An idea for a new product, or a modification to an existing design, requires both human effort and financial input if it is to come to fruition.
Part of the design process is the development of prototypes. A prototype is a ‘test’ version of the product, and may have different functions depending on when it is constructed during the design cycle. If the product is simply having a change to its styling, the prototype will be important in establishing the ‘look’ which will be attractive to consumers. If a new piece of technology is being used to improve a product, the job of the prototype may be more technical: to ensure that the product’s performance is up to scratch. Prototype development may be one of the most costly and time-consuming stages of finalizing the design; it may involve extensive market research, or prolonged laboratory and consumer testing.
If the design life cycle is shortened, to hasten the arrival of the new product in the marketplace, the risk of failure goes up. More designs for a product arriving faster on the shelves is good for consumers, who will revel in the choice, but not good for employers or employees who are staking money and jobs on success!
As an example, James Dyson is on the record as saying that the design of his cyclone vacuum cleaner came about after the making of 5000 prototypes.
The third case study I have chosen to continue the design story is an accessible example that allows me to look at some engineering specifics: it is the design and successful production of a folding bicycle. At the end of the study I shall consider the general lessons and issues that arise from the study. However, remember that most designs fall by the wayside, so its success makes it atypical.
2. BICYCLE ORIGAMI
Andrew Ritchie started designing a folding bicycle in 1975, stimulated by the Bickerton folding bicycle design. The Bickerton is made from aluminum, and is hinged at the chainwheel bracket. (The chainwheel is the toothed wheel driven by the pedals.) This means that the chain and chainwheel are on the outside when the bicycle is folded, and the two wheels come together.
In essence, Ritchie was inspired by the thought that he could do better. His two major criticisms were that the bicycle didn’t fold well because the chainwheel, the muckiest part of a bicycle, was prominent; and that he did not think that aluminum was the best material for a folding bike:
“Aluminium is too soft for a folding bicycle, it just doesn’t stand up to the knocks, the everyday wear and tear.” Ritchie (1999)
3. PROTOTYPING AND IMPROVING
In Ritchie’s first prototype design (P1) the rear wheel hinged forward in its own plane from the lowest point of its triangular support structure. However, unlike the production model, the front wheel of P1 also moved (almost) in its own plane underneath the bicycle to sit alongside its partner; in this case some sideways movement was needed to ensure that the front wheel sat next to the rear one, rather than just bumping against it as it hinged. To achieve this the front wheel needed a complex, skewed hinge to move it the few inches sideways so as to clear the rear wheel and chainwheel.
As well as moving the two wheels to the centre, it was necessary to move the saddle, together with its pillar, and the handlebars into the same space. The seat pillar telescoped to get the saddle into the packing space, which had the advantage that saddle height adjustment and packing were accomplished by the same mechanism. The telescoped seat pillar slid down behind the hinged rear wheel, so locking it in place, an important feature that has survived the transition from prototype to production.
Ritchie was driven by a search for ‘the ultimate in compactness’ when designing and building P1, which was a platform for various design ideas.
The chainwheel and the saddle competed for space in the folded package, so Ritchie tried to move the chainwheel away from where the saddle needed to be, but
“…it was too complicated, I gave up an inch when that idea was dropped.” Ritchie (1999)
Prototype P1 used 18 inch wheels, then common on children’s bicycles. The main tube of the frame was lower than in the production model and the bicycle was not stiff enough (see Stiffness and flexing). Bowden cables linked the front- and rear-wheel folding mechanisms.
Ritchie is a regular bicycle commuter in London, so he tests designs and design changes routinely and expertly. He was pleased with the realization of the basic design concept in the first prototype :
“I had demonstrated that the design concept could result in a compact folding bicycle.” Ritchie (1999)
Ritchie uses the expression ‘good luck rather than design’ to describe unpredicted advantages of his conceptual design solution.
4. THE SECOND PROTOTYPE (P2)
The major design difference between P1 and subsequent prototypes was the removal of the complex skewed hinge required to move the front wheel in its own plane underneath the bicycle to sit alongside the rear wheel. The front wheel now hinged orthogonal to the plane of the bicycle (i.e. it moved sideways from the line of the frame, as happens in the production model in Figure 46 (e) and (f)) using a purpose-designed hinge made from tubing.
The rear wheel continued to be folded underneath the frame. The P2 saw the introduction of castors on the rear luggage rack, on which the bicycle sat when the rear wheel was folded underneath. These too have survived.
Unlike the production model, P2’s handlebars hinged down, one each side of the package. Also unlike the production model, the seat pillar of P2 consisted of more than one tube which telescoped during folding.
Two more prototypes were built using sliding tubes to produce hinges, this time with 16-inch wheels. Wheel size is a key issue for the designer of a folding bike. Smaller wheels are easier to pack small, but the smaller the wheel the bigger the pothole feels! There is also the ‘make or buy’ decision to consider. Mass production of bicycle wheels is a big issue; it is much easier for a manufacturer to buy-in wheels produced by a large manufacturer than to dedicate machinery and labour to the production of wheels just for their own product.
A Brompton Prototype : Note the frame hinge on the crossbar
Andrew Ritchie’s intention was to sell the design. To further this ambition, he applied for and obtained a patent in 1981. You will read more about patents in the next unit, but for now it is worth noting that his patent may have been difficult to defend, owing to the number of previous designs of folding bicycle that were available. He certainly could not have afforded to defend it if his design had been copied by a large manufacturer, but nonetheless it is a formal statement of the design, a design representation, and a claim to intellectual property.
In total Ritchie built four prototype machines, with a low main tube, between 1975 and 1979, to prove and develop his ideas. His next problem was to turn the design into a product that you or I could buy.
5.1 THE FACTORY OPENS
Because Andrew Ritchie could not sell his idea, he decided to set up his own factory to manufacture the bicycles. He borrowed money from friends (the interest on the loans was a bicycle) to build 30 bicycles and 20 for sale.
After the increasing complications of the prototyping stage, manufacturing constraints become a powerful influence on the designer:
“Bending one top tube is difficult enough, bending fifty is really tiring.” Ritchie (1999)
The main tube was positioned higher and a simpler bought-in offset hinge replaced the purpose-built tube hinges. This forged hinge, which was critical to the Brompton’s development, was from France. So, detailed design changes were made to the hingeing system with some benefits to compactness resulting from positioning the hinge higher in the frame.
The telescoping seat pillar was dropped, becoming a single tube, and the frame was braced with a small diagonal cross-beam to give it extra stiffness.
“After the first 50 I got a small-firm government loan to produce batches of 50 bicycles; 400 in a year and a half.”Ritchie (1999)
5.2 BATCH PRODUCTION
“After the first 50 I got a small-firm government loan to produce batches of 50 bicycles; 400 in a year and a half.”
Ritchie (1999)
Designing and manufacturing low-cost tooling was a harder job for Ritchie than designing the bicycle. There are many design routes to producing a lighter frame or a more easily manufactured frame that are not available to a small batch manufacturer. He had to use soft, mild steel for the main tube as he could not bend stronger alloy steel, and the main tube had an aesthetically ugly kink from the bending process. Plastic parts were machined from the solid and metal plate was drilled, cut and bent. The process is essentially scaled-up craft production.
During this period Ritchie learned from customers, and from riding his own bicycle. Indeed, sometimes detailed redesign was necessary in the light of problems and failures brought to his attention by users. The business remained vulnerable, although there was helpful press exposure (See KEW FOR A RIDE below).
5.3 MASS PRODUCTION
In 1981 the French manufacturer of forged hinges discontinued production so Ritchie stopped batch production and wrote a Business Plan. After a hiatus of five years, in 1986, Ritchie eventually raised £90,000, half of the money he needed to go into mass production, from a customer, friends and family, and went ahead anyway.
The drive to design for manufacturability continues apace. A tool was designed to curve the main tube, so removing that kink. At the time of writing, 2000, a power press allows the use of a higher specification of steel for the main frame member. The hinges were machined from the solid until expensive forging tools could be bought in 1987. Ritchie is working on removing the skill from the manufacture of hinges
The material is taken from this website:
http://cozybeehive.blogspot.my/2008/11/design-case-study-innovation-of.html?m=1
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