Announced in the March 2000 Issue of Wired Magazine
Jump to: Contents of Plans - Interviews & Reviews - Championship Solar XR2


 

The Ground Hugger XR2 spent nearly two years on the "drawing board" before the prototype was built. The hardpoints and general layout are based on the well-proven original Ground Hugger design. Major technology differences include the XR2 's carbon fiber composite seat and frame, a rear suspension system, and the latest in cycling components and design.  In terms of esthetic design, the XR2 breaks new ground and makes a uniquely independent statement of its own. We call it our Ferrari on two wheels.
         Due to its composite construction, the XR2 is actually easier to build than its predecessor, which uses a welded metal tube frame.  And the carbon-fiber-over-urethane-foam construction method practically begs for creative design ideas.  So plans provide the information you'll need to modify and invent to your heart's delight.   Any type of bicycle can be built of this material, including long-wheelbase and short-wheelbase recumbents, and even conventional upright designs.   The possibilities are limited only by your imagination. 

Carbon Fiber Construction

         The frame and seat are built of hand-laid carbon fiber over a urethane foam core. The molds and vacuum bagging typical of conventional carbon fiber construction are unnecessary.  We've used vinylester resin, which is about half the price and nearly as strong as conventional epoxy. The main advantage of vinylester is that it's catalyzed and applied just like polyester resin, which makes it much easier to use for the do-it-yourselfer. 
         Lay-ups are applied to the urethane foam core, and the foam remains as an integral part of the frame. So the foam serves as a mold of sorts, and it adds significantly to the strength of the frame. Imagine bending a hollow metal tube to the point where it kinks and collapses. The same failure point occurs with any hollow structure, regardless of the material. But with a foam core, the walls of the structure (the carbon fiber skin) are held in place so they cannot kink and collapse. Even though the foam has little strength of its own, it plays an important role in the overall strength of the composite structure. 
        Metal fixtures are laminated in place at attachment points, such as the head, bottom brackets (there are two), steering tube, and rear suspension hardpoints.  The bottom bracket shells are purchased ready-made, and the other items are simply cut from lengths of aluminum tubing.  The photo of the foam core (in the left margin) shows the aluminum steering housing cemented in place.  The steering housing is made of thin-wall T6 aluminum tubing, and weighs 6.25 ounces (177.8 grams).  And if you strive for the absolute minimum in weight, up to half the mass of the headpiece, steering housing, and bottom bracket shells can be removed by drilling lightening holes (not done on the prototype).
         Table T1 provides a listing of materials and costs to build the seat and frame (exclusive of finishing materials).

Specifications

         Table T2 provides the weight of a few of the XR2's primary components. Specifications are provided in the Table T3.   

         Plans are available in printed format, and in a Deluxe set containing a CD-ROM with 3D electronic models, CAD drawings, an expanded electronic manual, and video clips of the XR2 in action. The CD works on an ordinary PC running Windows. All the necessary software is included. You do not need a CAD system to view the electronic CAD drawings and 3D model. Printed drawings include five 24 x 36-inch sheets, and one 34 x 60-inch sheet with full size patterns of the frame, seat, and rear stays. A full size pattern of the fork is also included. The construction manual includes over 100 photos and illustrations, detailed technical and design information, and step-by-step instructions on building the XR2. 

• Contents of the Construction Manual
• Screen capture of Sheet 1 of the CAD drawings (shown without annotations). 
• Preview of CD-ROM packaging (52kb).
• An overview of what's included on our CD-ROMs. 

Interviews and Reviews

• BikeRod&Kustom  During an interview with Jim Wilson, Webzine Editor of BikeRod&Kustom, Robert Q. Riley talks about the development and design details of the XR2.  In a separate article, Jim Wilson reviews the XR2 plans.

Noteworthy XR2 Projects

• Hybrid Solar XR2 Wins 2001 Australian World Solar Cycle Challenge (B-Class) Check out the championship solar-assisted hybrid XR2 built at Prince Alfred College in South Australia.