24-04-2012, 12:56 PM
Regenerative Braking System
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The Product Design Problem
Bicycles have been the heart of human transportation since the dawn of its creation. Many advances have been made to make the bike more desirable and friendly for the millions of users throughout the world. In many countries throughout Western Europe, a very large number of professionals use bicycles to commute to work in their business suits with their briefcases. It is our goal to design a device that can make their commute an easily traveled one. The Regenerative Braking System (RBS) is a device that can do so by reducing the overall energy the day to day business commuter is required to use.
Product Development Process
Many decisions need to be made in order to produce the most desirable and affordable product to make the highest profit and most unique device. The flow chart in figure 1 shows how our product fits into the product development process. There are three distinct phases: the Concept Phase, the Design Phase, and the Production Phase. During the Concept Phase, we defined the problem of losing energy while braking on a bicycle. We then conceptualized different ways of using that energy with different regenerative braking systems. Through research and customer surveys, we entered the Design Phase knowing consumer preferences. We generated designs based on known preferences, constraints, and parameters. We then made a CAD drawing of our design. We analyzed our model from the viewpoint of the consumer and manufacturer and did a profit analysis of the optimal designs. After reviewing our results, we hypothesized how we would enter the Production Phase. Because this product would be produced in bulk, we took into account the price of machinery, storage, labor, etc. After all of these costs were accounted for, we analyzed potential profit again to make sure we would still make money. Initial results indicate that we would eventually make a profit if this product were actually placed in the market.
(Insert flow chart)
Design Requirements
There are many requirements that need to be met to produce a product that is both feasible and optimal. There are also some constraints, both geometric and engineering that also need to be satisfied. The following list describes these requirements and constraints:
Store energy while braking
This is the main requirement and the overall objective of the device and must be suitable to meet the customer’s needs.
Interpretation of Results
The solver found that the minimum spring compression length is 0.35 meters, and by using a common rule of total spring length is 1.5 times the compression length the total spring length is 0.52 meters or almost 21 inches. The spring constant was chosen to be in a reasonable range of 25000 N/M, but the spring length seems to converge around the same optimal length as k goes higher. The only active constraint that is present is the final radius of the cone. This active constraint is expected because the smaller the final radius is the less the spring will be compressed and with the number of times the wheels rotate.
ANALYTICAL TARGET CASCADING
We have so far discussed how to optimize the RBS from three points of view: engineering, manufacturing, and customer. The engineer attempted to minimize the amount of spring deflection (x) for a given value of spring stiffness constant (k) based on a minimum stopping distance (D), which was derived from a physical description of the system. The manufacturer considered the effect of k and x on three design characteristics: cost to manufacture, weight of the product, and the capacity of the product to return energy to the rider.