Quote Originally Posted by Robin Hewitt View Post
There is a 2.5m axle across the back, I think 1.5" 10g aluminium tubing should be fine for that. At <2rps it should not get the shakes.
That's to link the belt drive I assume? If so the inertia of that tube will be immense; I=pi/2*7850*2.5*((38.1/2/1000)^4-(31.3/2/1000)^4)=0.0022kgm^2. To put that into perspective that's only half the moment of inertia of a 1.5" solid bar.

You'd probably be better off with bar. For 2rps critical speed and 2500mm length that's only 5mm diameter, so use anything between 5mm and 33mm solid bar and and have less inertia than the tube yet still have high enough critical speed. Tube will have higher torsional stiffness so could do with comparing that.