Regenerative Braking System
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Abstract
When riding a bicycle, a great amount of kinetic energy is lost when braking, making start up fairly strenuous. The goal of our project was to develop a product that stores the energy which is normally lost during braking, and reuses it to help propel the rider when starting. This was accomplished with a spring and cone system whose parameters were optimized based on engineering, consumer preference, and manufacturing models. The resulting product is one which is practical and potentially very profitable in the market place. A spring (of tension 22,100 N/m) is stretched (at most 37cm) by a wire which wraps around a cone (of 15 cm large diameter and 2 cm small diameter), while braking. A clutch is then released and the cone drives the bike’s gears to assist the rider while starting. The product weighs 14 lbs, will cost $87, and will return 85% of the rider’s stopping energy when starting up again.
1.1 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.
1.2 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.
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1.3 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:
1. 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.
2. Return energy to start up
Once the energy is stored in the device, it is necessary to have a simple way to release this energy back to the user in a positive way. This can be accomplished with an innovative gear system.
3. Must fit on a bicycle
This is one of the most difficult constraints to achieve and most important because we are dealing with such confined spacing. The objective is to fit the length of the spring on the longest part of the bicycle, which is slightly less than a meter.
4. Light weight
The importance of having a light weight design is driven by the customer’s desire to have a bicycle that is more maneuverable and more portable. This is also a direct trade off with how much energy can be stored in the spring.
5. Good stopping range
The stopping range is important because this product needs to be usable in real life situations. This component can be optimized to have the shortest stopping distance using dynamic analysis.
6. Good stopping force
The force required to stop is dependent on the stopping range and the comfort levels of the rider. It is also related to the possible spring features.
7. Inexpensive and affordable
This product must be able to make a profit and be desirable. The driving force for the price can be directly related to the spring size as shown later in the paper.
8. Safe to user and environmentally friendly
Safety is always a very important aspect when ever there is a consumer product. This requirement will be addressed after the initial design is created.
9. Profitable
Profit is usually the main motivation for the start of any company, therefore this is one of the parameters that will be optimized.
10. Reliable
It is important to have a product that is reliable and this requirement will affect the long term business image and needs to be maintained in high regards.
11. Manufacturability
In order to make anything profitable, it needs to be manufacturability, hence the important of having a product that can be made easily and cheaply.
12. Aesthetically pleasing
This is not a requirement that needs to be taken heavily, but the design should always have nice look about it, because looks will persuade the buyer.
13. Modular
Having a device that can be adapted to existing bicycles is essential to sell the greatest number of units. This also can reduce other types of manufacturing costs.
14. Should not hinder normal riding
To have a successful accessory for a bicycle, the ride should not feel a noticeable change in the biking performance or in the normal riding motion. A device that impedes the normal biking experience would be considered undesirable.
15. Controlled release
The energy that is released back to the user must be done in a safe and manageable fashion. This can be a consideration after the prototype is completed.
The main requirements that are used in the analytical model were reduced to price, weight and capacity (percent of the energy returned). All of the previous design requirements were used in the engineering model to describe the reduced requirements.
