A turbo trainer with a motor resistance braking unit is the most advanced that you can get, however in practice it has only have one advantage over an electromagnetic turbo trainer in that it can drive your back wheel thus simulating downhill riding more realistically. This only comes into play when you are riding on computer films or virtual reality environments where you follow a real-life course and thus sometimes go downhills. Only 5% downhill gradients can be simulated at this present time so this may not be a major selling point for you?
Motor turbo trainers follow a similar path to electromagnetic turbo trainers, but instead of spinning a steel disc relative to an electromagnet, motor brakes use a current carrying coil that is placed within a magnetic field (generated using electromagnets), and this generates a torque on the coil. This torque can be accurately controlled via the amount of current applied to the electromagnets and/or rotating coil, and thus you will need to pedal more powerfully when the electromagnetic field increases (e.g. the resistance increases). Similarly, the torque direction can be reversed to generate a driving torque to spin your back wheel.
Currently, only Tacx build motor turbo trainers, see their range below.
