A Dynamically Adjustable Bicycle Suspension Fork

This project consists of the design and construction of a prototype bicycle suspension fork with dynamic, electronically controlled compression and rebound damping. It is intended to meet the requirements of the University of Victoria's CENG/ELEC 499 Design Project.

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  • Market

    Mountain biking enthusiasts are constantly demanding more control over all aspects of the riding experience. The ability to tune the...

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  • Design

    The elektroshok system uses real time data collected from a MEMS multi-axis accelerometer along with a position sensor placed on the fork. This data...

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  • Media

    A browsable photograph lightbox and video player.

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  • Library

    Available documents and files for the project.

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  • Background

    This project consists of the design and construction of a prototype bicycle suspension fork with dynamic, electronically controlled compression and rebound damping. It is intended to meet the requirements of the University of Victoria's CENG/ELEC 499 Design Project.

    The system uses acceleration and inclination data from two analog MEMS inertial sensors along with position data from a magneto-potentiometer mounted to the shock piston. An on-board microprocessor quantizes and interprets the data and based upon the control algorithm, adjusts the shock characteristics. Two high-speed stepper motors allow interaction with the shocks rebound and compression valves. Additionally, the user can select different riding scenarios for shock performance, as well as create their own. This is done via a handlebar mounted display and joystick.

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  • Market

    Mountain biking enthusiasts are constantly demanding more control over all aspects of the riding experience. The ability to tune the damping properties of a mountain bike suspension fork has long been a desirable market feature.

    At the time of writing, there are many suspension forks on the market that have manually adjustable rebound and compression damping controls. Unfortunately, these manual controls require that the user set up the forks beforehand and have limited to no ability for on-the-go adjustments. This manual system often puts the rider at a disadvantage when they encounter an unexpected change in terrain. As such, single static setting for rebound and compression damping is simply not enough to ensure the optimum performance of the fork for the duration of a ride.

    The elektroshok system will improve the performance of a traditional suspension system by changing the damping properties based on sensor input and user defined settings.

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  • Design

    The elektroshok system consists of four major building blocks. These include the sensor system, the mechanical interface, the user interface, and the control algorithm. Combining these blocks allows full control of the bicycle's suspension. This allows the suspension to remain supple for maximum control on rough terrain while still ensuring the piston travel is tuned properly for large drops.

    We have implemented three key features for this system:

    1. Monitoring the terrain data and adjusting the rebound and compression damping appropriately
    2. Detection of a sustained incline will trigger lock-out of the suspension travel
    3. Preset modes for expected riding style and terrain

    This implementation and the four building blocks are discussed below.

    Sensor System:

    The elektroshok system is heavily reliant upon external sensors. One such sensor is the accelerometer. This device provides the most vital information. Extraction of both vertical and fore-aft acceleration information was vital, while ignoring the lateral acceleration. This requirement was satisfied by incorporating a two-axis accelerometer mounted on the plane of the bike. The ADXL278 dual axis accelerometer has an operating voltage of 3.6-5V and detects acceleration of +/- 35G on both axis.

    The other critical sensor needed for the elektroshok system was a position sensor. This was needed to determine the position of the shock at any time. A main design requirement was that there could be no contact between the upper and lower shock sections. The MP1 Magneto-Pot from Spectra Symbol is a contactless linear sensor that satisfies our design requirements. The sensor used in the system has a 150mm operating range, easily accommodating the full range of the shock.

    Mechanical Interface:

    The physical mounting and mechanical design of the elektroshok system was a problem that the team encountered early on. The sensor and motors needed to be mounted to the fork cleanly, as well as be protected from the rough conditions encountered while mountain biking. Secure housings and mounting brackets were crucial.

    The position sensor is housed inside of a protective ⅛” acrylic tube attached to the lower fork leg. A nylon bushing is located at the top of this tube and guides the magnetic marker along the track of the position sensor. The magnetic marker is attached to a long stainless steel rod, fixed to the upper fork crown by a clamp. The accelerometer housing is designed to provide a secure and rigid contact with the fork. In order to achieve this, the accelerometer is mounted directly on an aluminum plate, bolted to the disc brake tabs found on the lower left fork leg. The accelerometer and associated wiring will be placed inside of a plastic housing filled with potting compound.

    Selection of the stepper motors were based on measurements taken to determine the torque needed to rotate the compression and damping knobs on the fork. Several measurements were taken, to determine approximately 75 mNm are needed to rotate the adjustment knobs axially. Motors were chosen that would provide at least 1.5 times the needed torque. The Soyo Unipolar Stepper Motors provide 250 mNm of torque. Unipolar motors were chosen because the torque is held constant over a wider speed range versus that of a bipolar motor. The compression damping motor shaft will attach to the adjustment knob via a 12mm hex socket while the rebound damping will adjust via a 3mm hex key. The motors are held static to the fork via custom brackets mounted to the fork.

    User Interface:

    Our system offers a rich user interface experience. Visual feedback is given by a bright, full-colour, organic LED screen. This screen boasts a full 2.5” square viewing area, allowing shock modes and settings to be modified quickly and easily. A user can simply scroll through the menus, using the five position joystick. The user’s selections are shown onscreen, via pseudo three dimensional artwork. To further assist in navigation, a piezoelectric buzzer provides audible beeps, positively alerting the user to their selection.

    Control Algorthim:

    The functionality of the system has been designed to detect and adapt to the most common riding scenarios. The table below classifies each riding scenario supported by the UI. Additionally, the table outlines the adjustments to the compression and rebound damping for each case. The data from our sensor bank will be monitored and when a specific riding scenario is detected, the system will enter that mode of operation. This table forms the basis for the functionality of our system and allows for future expansion as more use cases are defined.

    Riding Style Compression Damping Rebound Damping
    Cross Country High Low
    Downhill Low Mid
    Mountain Mid Mid
    Road Full Low
    Race High Low
    Custom User Defined User Defined

     

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  • Media

    Photographs:

    Video:

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  • Library

    Below is a listing of available file downloads for this project.

     

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