How to calculate roller pitch(P) for roller conveyor?

1.  Calculation rule:  Please calculate roller pitch based on that conveyed product can contact  at lease 4 rollers.
     
        P<=conveyed product Length(L)/4


2. Sometimes, conveyed product can not directly contact roller because conveyed product’s bottom is not flat.
    So, we need to pay more attention to select roller pitch and roller load weight.