What is the exact formula for minimum radius of vertical convex /concave curves  in belt conveyors.Different books like rodenko/alexendrov/handbooks give differntformulae.I 've checked the design of a few conveyors in my plant and as per the formulae i have ,the radius come out to be around 250m for most of them . However actual radius given is 75 to 100m.There is no problem with those conveyors which have fluid couplings even with less  radius.However belt of those conveyors which have pin bush type couplings leave the carrying idlers during starting .So another question is that in calculating radius should we use belt tension  for pull out torque or operating belt tension. Also where do i find the elastic modulus of cotton belts and nylon belts with rubber cover.Indicative values will do. Belt supplier is not responding.Thanks in advance for replies