My Freemotion Elliptical developed a problem - the roller wheel was slipping off the rail, multiple times during a workout, even. This was at least a bit dangerous, and I noticed at least part of the reason was a worn out roller wheel (but also crappy design - short edge not holding the rail very well and a single roller to begin with). After finding a replacement online for well north of $100, I decided I'd try to design/print one myself. I designed the replacement in Fusion 360 copying the original, but also extended the edges to provide a longer arc and allow the wheel to hug the rail better. I used PETG for its flexibility and sturdiness, printed the replacement at 80% infill, bought some 10MM bearings (R10Z), and mounted the new wheel on my elliptical. I'm happy to report it hasn't fallen off the rail yet, and seems to be holding up well through multiple workouts!