When my friend Bryan Pate asked if I could build him an elliptical trainer he could ride outdoors like a bike, as a substitute for running, I was surprised he couldn’t buy it. Once I was convinced that it didn’t exist commercially, I set about designing one. After extensive 3D modeling, finite element analysis, and many design iterations, the ElliptiGO was born.
Having an adequate stride length was one of the critical aspects of achieving a fun, high-performance, non-impact running experience outside. To facilitate a long stride while minimizing overall bike length, I used an offset slider crank mechanism, with the crank pivot located behind the rear wheel, for the rider-to-drivetrain interface. I leveraged off-the-shelf bicycle parts when possible, including the 8-speed internally geared hub, which provides a great riding experience whether climbing or flying downhill.
I built the ElliptiGO in my garage in about six months. I fabricated everything on the bike myself, including bending the tubes, brazing the frame, and machining all the other custom components. I designed the frame to create a smooth, elegant, sweeping line that connects the bike’s functional points without interfering with the rider. I chose fillet-brazed 4130 chromoly steel tubing for the frame because it’s strong, doesn’t require post-weld heat treatments, and has an easier learning curve compared to welding. To minimize the frame’s weight I chose small-diameter, thin-walled tubing and got sufficient stiffness with a sweeping truss design.
One of the toughest parts was creating the two large radiuses out of plane bends in each of the four main structural tubes. The technique that finally worked involved packing sand in the tubes to prevent crimping and using a plywood fixture to get the target bend radius and angle while maintaining the proper phase angle between the two bend planes.
We are very pleased with the performance of this prototype. Bryan has put more than 1,000 miles on it, including a 50-mile ride where he averaged over 15mph, finishing in 3 hours and 16 minutes.
Now, we’re moving to production with a professionally built prototype. We’re currently taking deposits and expect to deliver bikes by the end of the year.
ElliptiGO video and news at elliptigo.com