Craig MacDonald, a Graduate Engineer at BVT was recently awarded the 2015 Ray Meyer medal for excellence in student design. Craig and his teammates; Ryan McKay, Charles More and Sean Syman were awarded the medal for their design work on a self braked zip line trolley that could travel down extremely steep slopes. The prototype zip line trolley they built has the potential to safely take a rider down a 400m high line dropping 150 vertical meters on Queenstown’s Coronet peak ski field.
The team undertook this design project for their final year project which counted towards their Mechanical Engineering Degree (Hons) at the University of Canterbury. Zip lines are a popular invention of the international adventure tourism industry; a cable is typically connected from one platform to another, often crossing a valley or using other natural gradients. Common zipline trolleys incorporate no braking, limiting zip lines to slopes of 10o to prevent the rider reaching dangerous speeds. The few zipline trolleys that do incorporate braking tend to use friction brakes which can suffer from significant wear. The industry sponsor of this project, Holmes Solutions, presented the idea of integrating their eddy current braking (ECB) system with a zip line trolley. This would provide a non-contact, constant velocity brake which removes the complications of wear and provides a smooth ride limiting all riders to the same speed. With the addition of the eddy current braking system zip lines would ultimately be able to access far steeper and more exciting terrain.
The team successfully designed and developed a fully functioning prototype that incorporated two brakes housed inside rollers above and below the cable, with the rider’s weight positioned on a lever arm to increase the frictional force. Additionally a mathematical model was developed that was capable of simulating the trajectory and velocity of a trolley as it travelled down and aid in the design of new ziplines. A temporary zip line was set up in Christchurch’s Spencer park in order to test the prototype. After overcoming some initial problems, involving a faulty brake and unwanted friction, the trolley functioned perfectly, aligning with the predictions made by the mathematical model. The zip line trolley they built clearly demonstrated the feasibility of incorporating eddy current brakes into trolley design and opens up a wide variety of possibilities for the adventure tourism industry in future.