The double wheel trolley is often used for zip lines. Double wheel in-line trolley rollers prevent the side-to-side twisting. Trolleys need to be built with a strong bearing capable of withstanding the forces encountered during the ride. The following trolleys are popular double wheel types.
Petzl Tandem Speed (Transport Pulley)Petzl Tandem Speed Pulley is used for cable sizes 1/4 to 3/8 inch, or 12 mm maximum, and speeds of 10 meters per second. This trolley has a dual pulley system which helps it track straight and reduce twisting. The trolley is opened and clipped around the cable then secured with the locking carabiner, which also connects the lanyard to the harness, to prevent it from coming off of the cable during the run. This zip line trolley has aluminum in-line sheaves mounted on self-lubricating bushings and side plates designed especially for movement and torsion encountered on a zip line. It can accept up to three carabiners for various purposes, including a backup lanyard run to a separate steel carabiner on the cable.
CMI Velocity Trolley is made for use on ropes courses and zip lines with maximum cable diameter of 1/2", 13 mm. It has high strength and provides a separate attach point for an additional locking carabiner. The additional attachment provides access for a backup or line to return the zip line trolley back to the starting position when done. As a backup, a separate steel carabiner is connected by lanyard and runs to another steel carabiner which the cable runs through. The CMI trolley is versatile and can be used with complex cable systems such as found in canopy research. The casing is made with strong stainless steel. It uses bronze bushings made with a sintering process that creates microscopic porosity in the bronze allowing lubrication to retain inside the bearing. This zip line trolley is 5" or 125 mm and has a width of 3" or 75 mm. It weights 3/4 pound or 1/3 kilogram. The CMI Velocity zip line trolley has a work load limit of 1,400 pounds, or 623 kg.
CMI Cable Trolley SS has an extremely high breaking strength at 14,000 pounds and excellent performance as a zip line trolley. It has stainless steel sheaves and has sealed ball bearings. The axle is stainless steel. It is made for rope or cable of 1/2" or 12.5 mm in diameter, weighs two pounds or 900 grams and has an attractive stainless steel finish. The CMI Cable Trolley SS is 6-1/4" x 6" in size. It also has a separate attachment point for an additional 'biner for backup or return pull line. The stainless steel makes it able to withstand the elements and provides corrosion resistance.
Fusion Climb Z-Max Speed Stainless Steel Pulley Grip Red Trolley Made with easy gripping "soft-grip" handle bar. Dual stainless steel sealed ball-bearings for durability with long wear alloy sheaves and super smooth ride. Capable of high speed, rated for 90 m/s. Has four attachment points for back up tethers. Requires a minimum Cable Size of 3/8". Dimensions are 11.4" x 6.24" x 7.98" and weight is 4 1/4 lbs.
Fusion Climb Unisex Tesa Speed Pulley Made with aluminum and stainless steel. The body is high strength alloy steel and aluminum side plates. This is a high efficiency trolley rated at 20 meters per second. It has smooth rounded edges for a comfortable feel and handling. The ball bearings are Aealed stainless steel. It is made for a 12mm Cable Rope. The dimensions are 4.24" x 3.14" x 1.08"
Zip Line Construction Guide. One of the few dedicated zip line construction books available. Excellent information, and a must have for anyone building a zip line without using a kit. Invaluable for both the backyard zip line builder and professionals. The book is black and white. PDF version is in full color and may be requested.
The Complete Ropes Course Manual. Learn how to run a challenge course from start to finish. It covers all the new ACCT certification content and how to effectively working with groups, course management, and technical skills required.