Adaptive Mountain Bike Braking System

Acknowledgements

Project Advisor: Chelsea Salinas

Technical Advisor: Dr. Joel Bach

Donations Made by: Mines HCDS

Video

Elevator Pitch

Adaptive mountain biking provides a recreational outlet for people with disabilities. For those who enjoy the descent, quad bikes are an excellent option, as it allows those who lack lower extremity control the ability to enjoy going downhill fast.  

However, current quadricycles require sufficient grip strength to utilize the brakes on the bike. This posed an issue for Adaptive Sports Center in Crested Butte, whose mission is to improve the quality of life for people with disabilities through participation in outdoor activities [3]. With no viable alternative for this problem, they reached out to the Human-Centered Design Studio in hopes of finding an effective way for those with limited grip strength or upper body control a way actuate the brakes.

The proposed solution is to let the riders use a supinating motion of their arms to use the brakes. The rider will hold on to vertical handles that use a cable routed through a pulley to pull the standard brake levers when these vertical handles are pulled via a supinating motion. This gives the rider full control over the brakes without needing to squeeze any levers, but instead rotate their arms. The finalized design will give Adaptive Sports Center the opportunity to provide the necessary adaptive equipment to a wider range of riders. 

Design Approach

Design Solution

The main components of the vertical braking system are as follows: The handle (black), the hand rest (red), the clamping part (dark green), the pulley (blue), cable guides (light green),  cable lever (yellow) and a couple of pieces of hardware.  

The system includes a dual-radius cable pulley mechanism (blue), a 90-degree torsion spring (not shown), and standard 22.2 mm bike handle grips to slide on the vertical handles (black). The handle screws out into the hand rest for ease of assembly and modularity in case of handle fracture. This handle will be 3D printed to be the diameter (22.2mm) – which is the diameter of a standard mountain bike handlebar – and length (150mm) – which is the maximum length of a lock-on bike grip [5] – to enable easy installation of standard bike grips. When rotated in a supinating motion, the handle returns to vertical via a 5 in-lb spring force from the 90° torsion spring seated within the handle.

The hand rest at the base of the handle in red will allow the rider to rest their wrist during a ride and is 82 mm in diameter based on the average human fist dimensions [6]. It attaches to the bike handlebars using the clamping mechanism shown in dark green. The clamping part is sized to fit standard mountain bike handlebars with two lateral bolts. Early iterations of the cable pull system included small protrusions meant to pull the cable like a lever arm; however, various modifications were made to the mechanism to lengthen the arc length of cable pull. The final solution includes a pulley, with slots to enable cable travel between small and large pulley radii, as well as a cable lever. This solution can achieve full engagement of the bike brakes when the handle is supinated 45° from vertical.  

Minor interference between mated components was a barrier worked through to ensure smooth supination of the handle. Additionally, tolerancing issues with 3D printing small cable guides caused unwanted friction, leading to multiple tolerancing modifications.  While the final design was initially intended to be either CNC machined or cast/molded (or have components of both as needed), the model demands complexity in order to perform the operations required and does not allow for either of these manufacturing processes. Due to this, the main components of the vertically oriented quad-brakes solution will be 3D printed using high-strength and high-temperature carbon fiber-reinforced nylon Onyx filament on a MarkForged 3D printer. 

This design offers the user the ability to utilize the existing mountain bike braking system with little to no alterations required, a simple installation process, efficient functionality, and robust construction. With a rotation of the arm, the existing brake lever pulls in, helping the bike come to a stop. This design has addressed concerns with previous designs, considered existing standards and dimensions, and adapted to challenges discovered along the way. 

Next Steps

The remaining work for the quad brakes is additional testing, as well as a slight redesign of a critical subsystem. A longstanding issue within the design process was generating enough cable pull to effectively actuate the existing brakes on the quad bike. The team decided on adding a pulley system to increase the cable pull. While this did increase the amount of cable pull by 200%, it introduced an increased amount of friction that could not be overcome. Future work will involve finding a better solution to provide enough pull length while minimizing the amount of friction in the design. The team’s next steps also lie in conducting tests on a quadricycle, as well as printing the design using carbon fiber–reinforced nylon Onyx filament. Once the team mitigates the friction and pulley issues, the design will be printed using this filament, and testing can begin on quadricycles, where we will gain valuable feedback to further refine the design. 

 Check out the Adaptive Sports Center of Crested Butte and their upcoming Adaptive MTB World Championships! Click this link for more information.

Meet the Team