..an unlimited speed drive shaft..
Is there such a thing? My guess is one approaching "unlimited" would be very short and very small diameter,(pocket size), if not smaller...
But for a useful driveshaft for a vehicle how can one be "unlimited" by speed?
The longer the length the slower you must run it before it starts to whip.
the smaller the diameter the same as above.
Wall thickness also affects speed limit, thin ones are rated slower.
If diameter is to big eventually there is a limit when it tries to come apart from the centripetal force (not likely in a vehicle application)
Just curious?