Rubber tubes and lines, etc., work pretty well for this, as long as it is light duty: I'm looking for a source of metal ones made for this purpose but have not found it.
If you use rubber tubes on Superstreets cars or with other real high RPM motors you have a vibration problem I've noticed - not due to the rubber hose, but just because of the slightly misalignment of shoaft. I've used rubber tubes to extend from the back 1/8 inch shaft out of SS vehcile motors to a custom-built frame behind the motor that holds a flywheel -- makes them run much more smoothly. But it takes a lot of fiddling and shimming and adjustment to get the vibration shake worked out of the alighnment.
