The BH Fitness R8 was the first machine I thought of as a FrankenTrainer. I built it for my wife, who found a conventional upright cycling position uncomfortable but still wanted an indoor workout that could respond to software.
Start with the person
The project began with the riding position, not the electronics. The R8 already supplied the seat, step-through access, and general posture that worked better for her. My job was to preserve those useful parts while replacing the closed exercise experience with something that could behave like a connected trainer.
That became a pattern for everything that followed: keep the part of a machine that suits the rider, then change only what stands between it and a more engaging workout.
A compact source of resistance
The Wahoo KICKR CORE fit the experiment because its leg crossbars could be removed and its body could sit close to the recumbent frame. I could treat the trainer as a compact resistance module instead of as a complete bicycle support.
This page is a project record rather than a fabrication recipe. The important idea is the separation of roles: the R8 handles human fit and the smart trainer handles controllable resistance.
Where it went
The machine eventually moved on to my son and wife. It was not the prettiest build in the workshop, but it established the reason FrankenTrainer exists: useful fitness equipment should not become irrelevant just because its original electronics are limited or its geometry falls outside the usual smart-trainer assumptions.