Some general backround - which may interest helicopter pilots.
Dave,
For gound vehicle applications the driveshaft very much defines the "performance envelope" for a given terrain. I normally recommend that for good off-highway performance you should be aiming to isolate the machine from inputs above 1Hz. This frequency is a comfortable walking pace, so the spine nicely cushions the brain from reasonable accelerations. A driver will then try to control his speed so that he remains in control of his vehicle, which is defined as being in good ground contact, so 1g +/-1g. We design suspension travel for 0g to 3g to give a little margin for misjudgment.
Large vehicles have the benefit of compliant tyres, so we can achieve the desired 1Hz for less supension movement. The nominal spring compliance is chosen to be above tyre compliance, so that we can use asymetric dampers. The asymetric damper has a much higher rate in rebound over bound, so that in bound the sping compresses along with the tyre and in rebound the damper can thus absorb enough potential energy to avoid overshoot. For my models i assuming a spring law of Force=Const*Dist^Exponent, for either air or rubber installation. The automotive guys use a package called ADAMS which pushes the ride&handling performance to a different level.
The practical upshot of all this is that for ground vehicles every effort is made to limit the travel that the drivelines have to endure. I can tell you that for anything i look at, i aim to keep the nominal angles between 1 - 3 degrees from unladen to laden, and i aim to keep relative UJ angles within 1 degree. Anything beyond that and the universal points do not last our powertrain design intent of 15'000 hours, since the accelerations cause huge dynamic loads to affect bearing B10 life. I doubt very much that many drivers realise how much thought has gone into such a seemingly simple component.
When i worked at Land Rover (before BMW sold it to Ford) i recognised that the Thompson coupling had the potential to overturn many of the old rules. For helicopters the suspension from the air turbulence is in the blades themselves. I think Nick is quite right in that the applications are more limited, but there are potentials for advancement - like intermediate gearboxes.
If i get any feedback from Thompson i will feed it back to this thread for all to benefit...