Experiment 2

The second experiment was carried out to find the maximum compressive force required to completely depress the forks. The results proved that the rate of depression was linear as compressive force increased; from 0kN through to 2kN. The following photographs indicate how the test rig was set up:

Experiment 1

In order to determine the effect of the suspension on braking distance it was necessary to conduct an experiment whilst adjusting the following parameters:
1. Velocity.
2. Braking Force.
3. Suspension setting (Locked out or able to move freely).

The following Photographs indicate how the experiment was conducted:

Latching solenoid

A latching solenoid would be a suitable device for operating a normally open locking mechanism. When the brake lever is pulled it could operate the solenoid that then slides the pin into the lock out mechansim rendering the suspension useless. This achieves the desired state and seems like a realitively straight forward way of achieving the aim.

Electrorheological Fluids

There are various descriptions of how this technology works but the basic breakdown is like so:
1. A fluid is made up of 2 seperate liquids (ie water and oil). When no electrical field is applied the one liquid is held within the other (ie water held within oil).
2. When an electrical field is applied the one fluid is driven to one side by electro Osmosis. This binds the adjacent particles together into chains which is what we call the solid state. (Electro Osmosis - Osmosis through a membrane that is caused by the action of an electric field, usually such a field generated by two electrodes, one on each side of the membrane) - http://www.yourdictionary.com/electroosmosis

The following link shows a video of Electrorheological Fluids in action:



The electrical field varies depending on the structural rigidity of the forces involved. I will need to conduct an experiment to determine the maximum compressive force involved before making a decision on the suitability of Electrorheological Fluids.

Design Type

Whilst researching this project I have come to realise that the speed of change from active suspension to a locked out state is paramount to the success of my design.
At present I have a few ideas on how to achieve a rapid change but feel the need to investigate further in order to insure that my design has maximum potential.

I've used the following criteria as a guide to check the suitability of a design for the task:
1. Ease of use. Is it a seperate operation from the braking system. If so - is it redundant in an emergency situation where the brake has to be used harshly and in a rush?
2. Speed of operation. Can the design operate before the suspension has began to dip?
3. Position on bicycle. Is it likely to hinder the rider before, during and/or after operation. For example attaching a large oil reservoir to the handlebars is likely to hinder operation of other moving parts (gears etc).
4. Cost. Is it feasible to produce and sell?

Electrorheological Fluid
These are a very versatile fluid that alter their state as electrical fields are applied. When no field is applied the particles are free to float around and in this case actively work as part of the suspension. When an electrical field is applied the particles are bound together to form a solid body. This solid body would suit the purpose of locking out the suspension. This option seems perfect for the application I desire however it would require the bicycle to constantly carry a suitable electrical power supply in order to maintain successful operation. This needs to be investigated further so I will post a further blog looking at the feasability of using Electroheological fluids, which will also consider the shear stress that the newly formed solid can withstand.
A more detailked analysis of Electrorheological Fluid can be found at:
http://en.wikipedia.org/wiki/Electrorheological_fluid

Standard Brake mechanism with secondary cable operating lock out.
At present FOX (amongst other manufacturers) have a product on the market that operates the lockout from a lever suitably positioned on the handlebars (shown below).


This device works when the rider has time to operate the lever but is redundant when rapid braking is required; unless it has been left in the lock out position. I propose that it is possible to adapt this design to operate from a secondary cable that is operated by the front brake lever. The secondary cable could be suitably tensioned to allow rapid operation of the lock out device when a suitable braking force (ie large) is applied.

Bicycle position sensor.
This design would negate the need for rider operated lock out. The design would simply engage the lock out when the bicycle is positioned facing downhill. An electrical power supply would operate the lock out when instructed to do so by a position sensor. This design would also require an override function so the rider can choose to turn the system off. The design would also require operation of the front brake before it worked otherwise the front suspension would permanently be locked out when travelling down hill; which renders it useless.

Investigating Lock out

After trawling through various websites and explanations I have discovered that Lockout is a key part of a serious mountain bikers gear.
The basic principle 'locks out' the front suspension forks which stops any movement. There are various mechanisms in use to achieve this change in suspension and they are all aimed at increasing the efficiency of pedalling.
Whilst this lock out increases efficiency it also increases the braking distance. I will need to measure this increase to avoid improving one problem and replacing it with another.

The different types of devices are shown below:

Standard Lockout situated on the actual fork - This requires the rider to reach forward over the bars and physically push the rotating slider into the lock out position.





Bar mounted Lock out.
This works on the same principle as the first Lock out; but allows the rider to control the lockout from an extra lever mounted on the bars.

All images shown where accessed on 1/11/10 and are from the following website:
http://www.highballblog.com/2010/07/lockout-mtb-suspension-fork.html

How Mountain Bike Suspension Works

This project will focus on the front suspension system utilised in many modern day mountain bikes. The rear suspension system will not be considered in great detail as it doesn't play such a vital role in altering the pitch of the bike under braking conditions.

Front Suspension utilises two main components; the SPRING and the DAMPER. These form the more commonly known SHOCK ABSORBER. The SPRING provides linear vertical movement and allows the bike to absorb the bumps. The DAMPER stops the SPRING violently reacting to compression; and therefore regulates the rate at which the SHOCK ABSORBER returns to the neutral position.

The following link explains how Mountain Bike suspension works.
http://adventure.howstuffworks.com/outdoor-activities/biking/mountain-bike4.htm

Compression Damping Video

The following link explains how to adjust a front suspension fork: http://www.ehow.co.uk/video_2360992_adjusting-front-suspension-damper-settings.html

This correct setup of the front suspension will allow the bike to remain stable under braking although it is still possible for a dramatic change in weight distribution to occur.

The aim of this Project is to create a device/system that will enable the rider to remain in control of the bike; even under extreme braking conditions.