[ODE] what are advantages of dAMotorUser?

[Krystian Ligenza]

Hi,

I must correct way my ragdoll behave. In most for bone-joints Im using 
universal joint, but there are few that have ball and amotor joint. As 
for now Im using  dAMotorEuler and have strange jitering in a motion. 
What are the advantages of using dAMotorUser?

Thank you!
Krystian