Axle on rollers

Leonardo studies with interest friction forces, which he calls confregazione (rubbing). He distinguishes between sliding friction and rolling friction. This chart axle is an application of his studies. Leonardo draws a system of pivots which, instead of being directly inserted in the wheels, rests on cylindrical rollers. Thus, the friction created by the weight of the chart is reduced by the revolving of the rollers on the wheel axle.
Codex Ashburnham 2037, sheet 9 r. 1487-92