AUTO GEAR SHIFTING FOR BICYCLE

Bicycle gears have been one of the reasons that keep a lot of people from cycling more often. This may sound a bit funny as gears are actually supposed to make work easier, especially when navigating through hilly areas, but the most people are never sure which gear they should be in for a specific terrain.
The good news is that with advances in technology, there exists bikes that are able to turn the gears based on the rider’s cadence.

Background information 

Bicycles are pedal driven, human powered machines which have two wheels attached to a frame. Though we have sketches of bicycles alleged to have been drawn in 1493, the first verifiable, practically used bicycle belonged to Baron Karl von Drais, a German civil servant who served the Grand Duke of Baden, Germany. This design was patented in 1818. Chained bicycles first appeared in 1869 and since then, the bicycle has been developments as shown in figure 1.  Bicycles have grown into being the main means of transportation in many regions today. They are also used for recreation, courier services, fitness, and as children’s toys.


Figure 1: Bicycle development history
 As regards the general appearance of the bicycle, not much has changed since the first chain driven bicycle was made in 1885. However, it is in the area of enhancements that the bicycle has really been transformed. With the advent of modern materials, the bicycle has been improved to become stronger and lighter. Carbon fibre bicycles are, for example 3-4 times lighter than alloy bikes and at the same time 3-4 times stronger.

Huge strides were made with the introduction of the mountain bike, enabling riders to navigate otherwise difficult terrain with relative ease. A further development saw the development of the electronic gear shifting which allowed for faster gear shifting by using switches connected wirelessly or by wire to a battery and motor which drives a derailleur as the one shown in figure 2. It is this bike technology that provides the basis for developing the auto gear shifting bike.

Figure 2: Bicycle’s rear wheel fitted with a derailleur
 How the auto gear shifting bike works

This bike is fitted with sensors which collect data which it uses, together with the riders specifications, to establish the most efficient cadence, based on, among others, the present cycling demands. It then establishes which of the available gears should be engaged. If there is a need to change the current gear, it instructs an electronic shifting system to do so.

Some of the available types allow for a manual override for a specific duration of time e.g. 5-10 seconds. These bikes allow the rider to also select their preferred rotations per minute value thereby ensuring that the bike is as close to your needs as possible.

The bicycle uses a complex algorithm to increase the bike’s efficiency by helping avoid situations where the rider is either out of optimum because they are too tired, distracted or lazy to change into a more appropriate gear for the current terrain.

The physical difference this bike has with preceding bikes is that it has no buttons and instead, the rider taps on the shifters to induce functions or control the entire menu. However, this also depends on the model.

How to achieve auto gear shifting for bicycle

What happens in a normal bike is that when you press the shifters, they adjust the length of the cables to select the desired gear. They operate on either an internal hub or a derailleur mechanism. In this project, this task is automated by using servo motors. The task is to incorporate the servos which change the effective length of the cable to the shifters and derailleurs to enable the bike change gears. Using the Arduino Mega, a program is created including the specific settings desired as optimum. For example, a cadence of 80 rpm is considered by a lot of riders as optimum. The system is desired to maintain this optimum cadence and if it falls below a set amount, let’s say 60, the Hall Effect sensors will pick up this signal and the system will be triggered to change to a higher gear. If it rises above the set optimum e.g. to 95 rpm, the system will trigger a change to a lower gear. These can be set based on a specific end user to allow the bike to be customised. The servos are powered by a battery but it is also possible to redesign to include an alternative power source, e.g. a dynamo.

In order to realise this project, the following components are required;

  • A suitable bicycle on which to modify (a mountain bike)
  • A suitable microcontroller: I suggest the Arduino Mega together with its project box since it is easy to use and has enough inputs and outputs pins.
  • Servo motors (4)
  • Servo controllers
  • 12V battery
  • Hall effect sensors (4)


Prerequisites

  • Arduino programming skills
  • Electronic skills and basic mechanic skills.


Advantages and disadvantages of the auto gear shifting for bicycle

While compared to a mountain controlled bike, the auto gear has the following advantages;


  • It removes the necessity for the biker to switch the gear and thereby increases the ease and comfort of use.
  • It allows the rider to input specific settings and then work based on them meaning that it allows for personalisation of the bike, a feature not possible with the preceding bikes.
  • Can be used by athletes to improve their performance levels by helping with regards to pacing. The bike can tell if you are above or below your targets.
  • It has no buttons and therefore no need to shift your hand while riding. All control is done using the shifters.


Disadvantages

  • Limitations in manual override can deny the biker the full control of the bike.
  • Reliability issues can be detrimental based on the number of sensors as well as the associated algorithm.
  • The associated cost
  • Depending on the added electronics, there can be a weight problem


References
1. http://www.gizmag.com/autobike-shifts-gears/29135/
2. http://www.cyclingweekly.co.uk/news/latest-news/bioshift-promises-automatic-gears-bike-151859
3. http://www.dcrainmaker.com/2014/10/bioshifts-automated-shifting.html
4. http://hackaday.com/2013/01/18/building-an-automatic-bicycle-transmission-in-a-week/
5. http://www.instructables.com/id/DIY-Electronic-Derailleur/

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