The Friction node can optionally be added on gear pairs. In cases where friction
is included on a gear pair, frictional forces in the plane perpendicular to the line of action are added on both gears.
By default, there is no friction on Gear Pair and
Rack and Pinion. It is, however, included for
Worm and Wheel. The worm and wheel pair has always neither a parallel nor an intersecting configuration and in this configuration there is always a slip even under perfect conditions.
where Ff is the friction force,
μ is the frictional coefficient,
N is the normal force,
v is the slip velocity, and
v0 is the characteristic slip velocity. The term
where Ff,r and
Ff,max are the additional sliding resistance and the maximum friction force, respectively.